9-V Battery Replacement

This circuit was originally designed to power a motorcycle intercom from the vehicle supply system. This type of intercom, which is used for communication between driver and passenger, generally requires quite a bit of power. In order to improve intelligibility there is often elaborate filtering and a compander is sometimes used as well. The disadvantage is that a battery doesn’t last very long. You could use rechargeable batteries, of course, but that is often rather laborious. It seems much more obvious to use the motorcycle power supply instead.

9-V Battery Replacement Circuit Diagram


A 9-V converter for such an application has to meet a few special requirements. For one, it has to prevent interference from, for example, the ignition system reaching the attached circuit. It is also preferable that the entire circuit fits in the 9-V battery compartment. This circuit meets these requirements quite successfully and the design has nonetheless remained fairly simple. In the schematic we can recognise a filter, followed by a voltage regulator and a voltage indicator. D1, which protects the circuit against reverse polarity, is followed by an LC and an RC filter (C3/L1/L2/C1/R1/C2). This filter excludes various disturbances from the motorcycle power system. Moreover, the design with the 78L08 and D3 ensures that the voltage regulator is operating in the linear region. The nominal sys-tem voltage of 14 V can some-times sag to about 12 V when heavy loads such as the lights are switched on.

Although the circuit is obviously suitable for all kinds of applications, we would like to mention that it has been extensively tested on a Yamaha TRX850. These tests show that the converter functions very well and that the interference suppression is excellent.

Author : Lex de Hoo - Copyright: Elektor

Rev Counter for Mopeds

Older mopeds are not usually fitted with a rev counter, which is a bit of a shortcoming. The making or finding of a suitable indicator instrument or display is often the greatest obstacle for the hobbyist. The author of this circuit has devised a practical solution to this problem in the shape of a (cheap) bicycle computer. Such bicycle computer is easily attached to the handle-bars and it usually has a large and very readable display.

The moped engine’s generator is used to detect the rev speed. The generator is connected directly to the engine drive shaft and generates an AC voltage for the on-board electrical system. The frequency of this voltage corresponds with the rev speed of the engine. This frequency, however, is too high to be used directly by the bicycle computer. The solution for this is to divide the frequency of the signal by 16, using a binary counter of the type 7493, before connecting it to the cycle computer.


Rev Counter for Mopeds Schematic


The generator signal is first rectified by D1, R1 and D2 and then limited to 2.5 V. Transistor T1 turns it into a usable logic signal. Counter IC1 contains four flip-flips, one after the other, which divides the signal by 16. This signal drives, via T2, the white LED D3. LDR R6 reacts to the blinking LED and is connected to the cycle computer in place of the supplied wheel sensor.  The generator signal also sup-plies the power for the circuit. D4/C1 provide rectification and filtering, after which the voltage is regulated to 5 V byT3 and D4.

For a correct read-out (calibrated rev counter), the bicycle computer needs to be adjusted for a wheel circumference of 889 mm or 89 cm (wheel diameter 28 inch).  Make sure that when building the circuit it is suitably protected against vibration and moisture. Mount the LED and LDR directly opposite each other and keep in mind that they need to be well shielded from ambient light.

LM1812 Ultrasonic-Transceiver

The LM1812 is a complete ultrasonic transceiver on a chip designed for use in a variety of pulse-echo ranging applications. The chip operates by transmitting a burst of oscillations with a transducer, then using the same transducer to listen for a return echo. Ifan echo of sufficient amplitude is received, the LM1812 detector puts out a pulse of approximately the same width as the original burst. The closer the reflecting object, the earlier the return echo.

Ultrasonic-Transceiver Circuit Diagram


Echos could be received immediately after the initial burst was transmitted, except for the fact that the transducer rings. When transmitting, the transducer is excited with several hundred volts peak to peak, and it operates in a loudspeaker mode. Then, when the LM1812 stops transmitting and begins to receive, the transducer continues to vibrate or ring, even though excitation has stopped. The transducer acts as a microphone and produces an ac signal initially the same amplitude as the transmit pulse. This signal dies away as is governed by the transducer"s damping factor, but as long as detectable ringing remains, the LM1812"s detector will be held on, masking any return echos.

50W Hi-Fi amplifier with TDA7294

The TDA7294 is a Hi-Fi amplifier and can give 100W RMS but with 10% distortion. Supplying 30 Volts you can have 50 Watts RMS with 1% distortion. Frequency range start at 16Hz and can reach 100KHz. Make sure you are using good heatsink. The chip supports mute function as well.

50W Hi-Fi amplifier Circuit Diagram


A symmetrical 30V power supply is all its need to power the unit. 

Schematic 22 Watt Audio Amplifier

The 22 watt amp is easy to build, and very inexpensive. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts. The circuit is not mine, it came from Popular Electronics.

22 Watt Audio Amplifier Circuit Diagram


Parts :

R1 39K 1/4 Watt Resistor
C1,C2 10uf 25V Electrolytic Capacitor
C3 100uf 25V Electrolytic Capacitor
C4 47uf 25V Electrolytic Capacitor
C5 0.1uf 25V Ceramic Capacitor
C6 2200uf 25V Electrolytic Capacitor
U1 TDA1554 Two Channel Audio Amp Chip
MISC Heatsink For U1, Binding Posts (For Output), RCA Jacks (For Input), Wire, Board


  • The circuit works best with 4 ohm speakers, but 8 ohm units will do.
  • The circuit dissipates roughly 28 watts of heat, so a good heatsink is necessary. The chip should run cool enough to touch with the proper heatsink installed.
  • The circuit operates at 12 Volts at about 5 Amps at full volume. Lower volumes use less current, and therefore produce less heat.
  • Printed circuit board is preferred, but universal solder or perf board will do. Keep lead length short.

12W Stereo Amplifier TDA1521 / TDA1521Q

This is a stereo audio amplifier circuit that provides 12W output power on each audio channel. This simple circuit is built on a single integrated circuit of TDA1521 / TDA1521Q, and only supported by few external components.

12W Stereo Amplifier Circuit Diagram


TDA1521/TDA1521Q is a dual high-fidelity audio amplifier encapsulated in a plastic 9-leads. The device is specially designed for power supply applications (eg, stereo TV and radio).

TDA1521/TDA1521Q features: Requires very few external components Low offset voltage between output and ground Input muted during power-on and off (no switch-on or switch-off clicks) Hi-fi according to IEC 268 and DIN 45500 Excellent gain balance between channels Short-circuit-proof Thermally protected This hi-fi stereo power amplifier is designed for mains fed applications. The circuit is designed for both symmetrical and asymmetrical power supply systems. An output power of 2 x 12 watts (THD = 0,5%) can be delivered into an 8 W load with a symmetrical power supply of ± 16 V.

LM3410 LED Driver

The LM3410 IC is a constant current LED driver useful in either boost con-verter or SEPIC design applications. A SEPIC (Single Ended Primary Induct-ance Conver ter) design allows the power supply’s output voltage to be set above, below or equal to its input voltage. In this application the chip is configured as a boost-converter (i.e. the output voltage is greater than the input voltage).

LM3410 LED Driver Circuit Diagram


The LM3410 is available in two fixed-frequency variants. Using either the 525 kHz or 1.6 MHz clock version it is possi-ble to build a ver y compact LED driver. The output stage can supply up to 2.8 A, allowing several high-power LEDs to be driven from a rechargeable Lithium cell or several 1.5 V bat-teries. The chip also features a dimmer input giving simple PWM brightness control.Output current is defined by an external shunt resistor. To keep losses low the LM3410 uses an internal voltage reference of just 190 mV.

Power dissipation in the shunt resistor is therefore low. Using the desired value of LED current the value and power dissipation of the shunt resistor is given by:
R_Shunt = 0.19 V/I_LED
P_Shunt = 0.19 V*I_LED

A 10 µH coil (L1) will be suf ficient for most applications providing it has a suitable satu-ration current rating. The Input and output capacitors should be 10 µF ceramic t ypes with a low value of E SR . Many distributor s including Farnell stock these component s. The Diode should beaSchottky type (as in all switching regulators). The author has developed a PCB for this design; the corresponding Eagle files can be freely downloaded from www.elektor.com/090850. In sum-mar y the most important features of the LM3410 are:

  • Integrated 2.8 A MOSFET driver.
  • Input voltage range from 2.7 V to 5.5 V.
  • Capability to drive up to six series connected LEDs (maximum output 24 V).
  • Up to 88 % efficiency.
  • Available is 525 kHz and 1.6 MHz versions.
  • Allows both boost and SEPIC designs.
  • Available in 5 pin SOT23 or 6 pin LLP outline.

Water Alarm Schematic

The LM1830 fluid detector IC from National Semiconduc tor is designed to be able to detect the presence of fluids using a probe. This chip requires a relatively high supply voltage and is not the most frugal power consumer. It is also quite specialised so unless you are buying in bulk the one-off price is not cheap.

An alternative circuit show n her e uses a standard CMOS IC type 74HC14. It has the advantage of operating with a 3 V supply and consumes less than 1 µA when the alarm is not sounding, this makes it ideal for use with batteries.

Water Alarm Schematic Circuit Diagram


The 74HC14 has six inverters with hysteresis on their input switching thresholds. A capacitor (C1) and a feedback resistor (R1) is all that’s necessary to make an inverter into a square wave signal generator.

In the water alarm circuit the feedback resistor consists of R1 and the water sensor in series. R1 prevents any possibility of short-circuit between the inverter’s input and out-put. Resistor R2 defines the inverter’s input signal level when the sensor is not in water. Any open-circuit (floating) input can cause the inverter to oscillate and draw more current.The remaining inverters in the package (IC1.B to IC1.F) drive the piezo buzzer to produce an alarm signal. Capacitor C2 ensures that no DC current flows when the circuit is in monitoring mode (with the alarm silent) this helps reduce the supply current.

A micro-switch can also be substituted for the water sensor to make the circuit a more general purpose alarm generator.

Author: Roland Heimann - Copyright: Elektor

Discrete Low-Drop Regulator

This circuit was designed to ensure that an amplifier circuit containing a TDA1516Q would not exceed its maximum supply voltage when the load is small. This amplifier is used in a PC to increase the audio power somewhat. The PC power supply, however, created so much interference that an additional power supply was required.

Discrete Low-Drop Regulator Circuit Diagram


The power supply has its own power trans-former with a secondary voltage of 12 V AC. After rectification and filtering this results in a DC voltage of about 16 V. The regulator consists of a P-channel MOSFET SJ117, the gate of which is driven via a voltage divider connected to T2. The base of T2 is held at a constant voltage by LED D2, so that the volt-age across emitter resistor R2 is also constant and therefore carries a constant cur-rent. When the output voltage is higher than about 13.5 V, zener diode D1 will start to con-duct and supply part of the current through R2 — as a result the MOSFET will be turned on a little less. In this way there is a balance point, where the output voltage will be a little over 13.5 V (1.5 V across R2 plus the 12 V zener voltage). The regulator is capable of deliver-ing up to about 2 A — in any case it is a good idea to fit the MOSFET with a heatsink.

It is possible to add an optional potentiometer in series with the 12-V zener diode, which will allow a small amount of adjustment of the output voltage.The relay at the AC powerline input ensures that the power supply is only turned on when the PC is turned on. This relay is driven from a 4-way power supply connector from the PC.

Author : Jac Hettema – Copyright: Elektor

Multitasking Pins

It’s entirely logical that low-cost miniature microcontrollers have fewer ‘legs’ than their bigger brothers and sisters – some-times too few. The author has given some consideration to how to economise on pins, making them do the work of several. It occurred that one could exploit the high-impedance feature of a tri-state output. In this way the signal produced by the high-impedance state could be used for example as a CS signal of two ICs or else as a RD/WR signal.

Multitasking Pins  Schematic


All we need are two op-amps or comparators sharing a single operating voltage of 5 V and outputs capable of reaching full Low and High levels in 5-V operation (preferably types with rail-to-rail outputs). Suitable examples to use are the LM393 or LM311.The resistances in the voltage dividers in this circuit are uniformly 10 kilohms.

Consequently input A lies at half the operating voltage (2.5 V), assuming nothing is connected to the input or the microcontroller pin connected is at high impedance. The non-inverting input of IC1A lies at two-thirds and the inverting input of IC1B at one third of the operating voltage, so that in both cases the outputs are set at High state. If the microcontroller pin at input A becomes Low, the output of IC1B becomes Low and that of IC1A goes High. If A is High, everything is reversed.

Author : Roland Plisch - Copyright: Elektor

Automatic Aquarium Feeder

People come in all shapes and sizes and we all have our own character. You probably know people who are at their best first thing in the morning while others can only get things done when they are burning the mid-night oil. The feeding habits of different fish species also show variation; some (such as catfish) are nocturnal feeders while others feed during the day. Unless your own body clock is in sync with the fish in your aquarium you will not be providing them with food when they really need it.

The solution described here is an automatic fish food dispenser. On the mechanical side the apparatus consists of an off-the-shelf DC mo-tor and reduction gear driving an external gear train sandwiched between two plates. It is necessary for the spacing between the plates to be greater than the thickness of the fish food pellet (see illustration).

A hole in the upper plate is directly beneath a vertical tube (or magazine) which contains a stack of food pellets. The hole in the lower plate is offset and the pellets will eventually drop through here into the aquarium below. In between these holes is the final cog in the gear train which has a hole made in it between the hub and toothed edge of the wheel. The hole must be slightly bigger than the diameter of the food pellet.

Automatic Aquarium Feeder Circuit Diagram


When the hole is beneath the column of pellets a single pellet drops down into the hole in the gearwheel. At each feed time the pellet is swept around until it passes over the hole in the low-er plate where it drops through and provides a tasty snack to the fish waiting below. The prototype uses a motor/gearbox combination from Conrad Electronics (model catalogue, part no. 242535) which operates on 3 to 6 V and produces an output speed of 11 to 22 rpm. An external set of gears provides a further 10:1 reduction. The final output gear takes around 30 seconds to complete one revolution and the low operating speed helps to avoid the possibility of a pellet becoming jammed in the mechanism. The frequency of feeding is actually controlled by an external mains time-switch which switches a mains adapter powering the whole feeding mechanism. The electronics incorporated into the feeding mechanism ensures that each time the feeder is switched on it only dispenses a single food pellet. Modern time-switches can be programmed to switch several times in every 24hr period and can have an ‘on’ time of one minute or less.

A small cam on the gear train output shaft actuates a micro-switch when a single revolution is completed. This technique of tuning the whole unit off in between switching times means that the standby current (excluding time-switch consumption) is zero. Another advantage is that each time the circuit is powered up it effectively performs a reset so it is not possible for the circuit to lock-up in an undefined state which sometimes occurs in digital circuits as a result of glitches and mains-borne interference. The central logic element in the circuit is the TTL SN74LS76N J-K flip flop. In addition to the synchronous functions of this chip (store, set, reset and toggle) there are two asynchronous in-puts namely ‘preset’ and ‘clear’ which are both active-low on this particular version of the flip flop.

When power is applied to the circuit the preset input of IC1A is held low by the RC network R6 and C4 which ensures that the flip flop will always be set (Q = 1) at power up. Transistor T1 switches on and the motor be-gins turning. A feeding cycle can also be initiated by pressing the manual pushbutton. When the output gear wheel has completed one revolution and pushed a pellet over the hole in the lower plate a cam on the output shaft activates a micro-switch. This will ground the ‘clear’ input of IC1B and produce a negative going signal to the clock input of flip flop IC1A which clocks the state of the J input (0 V) through to the Q output to turn off T1 and the motor. The ‘preset’ and ‘clear’ inputs of IC1B are connected directly to the micro-switch output to provide a debounce function ensuring that a single clean clock edge is provided to IC1A. All the other inputs of IC1B related to synchronous operation are unused and tied to ground (logical 0).

Capacitors C2 and C3 should both be ceramic types and although reservoir capacitor C1 is shown as a tantalum a normal electrolytic type can be substituted. The motor together with the circuit draws around 35 mA. A 50 mA fuse (F1) is included in the supply to protect the motor and transistor should a food pellet become jammed in the mechanism and stall the motor. A more powerful motor can be used in the design but in this case it will be necessary to re-duce the value of R4 to give a greater drive current and swap T1 for a power transistor. The fuse rating will also need to be beefed-up to handle the increased current.

A tip when drilling the plates is to start by making just two holes through the plates and then fit-ting two pins or bolts through the holes to fix the plates together be-fore drilling the remaining holes that are common to both plates. This ensures that the holes will be properly aligned.

Although the design was developed for feeding fish it could also be adapted fairly easily for other applications that require a programmable momentary mechanical operation.

Power Controller for Electric Convector Heaters

In Autumn or Spring, the weather may be warm enough that we’d like to save money by shutting down the main heating system in our home and just use supplementary heating based on one or more electric convector heaters.

Even though these convectors are quite heavy consumers of electricity, this can be reduced by f it ting a power controller between the heaters and the AC power outlet, which will affect the effective power consumption of the convectors.

Power Controller for Electric Convector Heaters Schematic


The circuit diagram is based around the use of the emblematic NE555 IC, used here as an astable multivibrator with variable duty cycle (D= thigh/ T), but at a fixed operating frequency, given by: f= 1 / (0.693 × P1 × C6) = 0.0654 Hz

The duty cycle Dof the signal at the output (pin 3) of IC2 will change depending on the position of the wiper of potentiometer P1:

  • If the wiper is at mid-travel, the duty cycle D will be 0.5;
  • If the wiper is at the +12 V end, the IC2 output signal is zero and hence D = 0;
  • If the wiper position takes it down to the voltage on C6, IC2’s output supplies a constant voltage of around 11 V and D = 1.

Byway of transistor T1, IC2 drives two MOC 3021 phototriacs (IC 3 & IC4) which provide the isolation between the circuit’s ‘driver’ section and the ‘power’ section, which is directly connected to the AC powerlines.

Each phototriac drives a power triac (TRI1 & TRI2). These two triacs are fitted in parallel and share the task of supplying the convector (RL): one triac supplies the positive half-cycle while the other triac supplies the negative half-cycle. The over-rating of the triacs (high rms current rating: 16 A) combined with their use in parallel and the alternating switching is aimed at reducing heating in the two components and reducing the bulk of the heatsinks employed. Experimentally, this solution gives rise to low heating of the heatsinks when the controller is powering a 2 kW-rated convector constantly (duty cycle D= 1).

The power consumed by the convector with controller is easy to calculate from the simple formula W= P× t× D where W =power consumed in watt-hours (Wh);P =rated convector power in watts (W);T =operating time of the convector/controller unit in hours (h); D =duty cycle set by potentiometer P1.

Example: for a duty cycle Dof 0.5 and an operating time of one hour, a 2 kW convector will consume 1 kWh.


Author : Gérard Guiheneuf  Copyright: Elektor

3000W Power Inverter 12V DC to 230V AC

Circuit Diagram of 3000 watt power inverter 12V DC  to  230V AC

Circuit Diagram of 3000 watt power inverter 12V DC  to  230V AC

Fig. 2: Sine-wave voltage and conventional square wave voltage with both 230 Volt rms


Fig. 3: Square wave voltage with duty cycle 25% for 230 Volt rms ("modified sine")


PCB Layout:3000 watt power inverter 12V DC  to  230V AC

Component Placement: 3000 watt power inverter 12V DC  to  230V AC

fig.: output voltage with no load or inductive load.

fig.: resistor 0,001 Ohm made of high-grade steel sheet metal

Control electronics | 3000 watt power inverter 12V DC  to  230V AC

fig.: control electronics on strip hole plate (previous version) and PCB of the "professional edition"

Assembly of the mosfet-transistors on the heat sink | 3000 watt power inverter 12V   DC  to  230V AC

fig.: heat sink, mosfet transistors, connections.

Final assembly | 3000 watt power inverter 12V DC  to  230V AC

fig.: 1500 VA inverter with 2 parallel transformers and 1000 VA inverter


Source: http://streampowers.blogspot.com/2012/09/3000-watt-power-inverter-12v-dc-to-230v.html

Particularly LM317 Circuit With 12v Battery Charger Circuit

The LM317 is AN adjustable three terminal transformer that is capable of supply 1.2 to 37 volts with a secure 1.5A output current. The LM317 is prepackaged terribly} normal electronic transistor package that makes it very simple to mount in your circuits.




The LM317 series of adjustable 3-terminal positive voltage regulators is capable of supply in more than 1.5A over a 1.2V to 37V output vary. they're exceptionally simple to use and need solely 2 external resistors to line the output voltage. Further, each line and cargo regulation square measure higher than normal mounted regulators.

In addition to higher performance than mounted regulators, the LM317 series offers full overload protection out there solely in IC's. enclosed on the chip square measure current limit, thermal overload protection and safe space protection.
The LM317 makes AN particularly easy adjustable change regulator, a programmable output regulator, or by connecting a set electrical device between the adjustment pin and output, the LM317 may be used as a preciseness current regulator. provides with electronic conclusion may be achieved by clamping the adjustment terminal to ground that programs the output to one.2V wherever most masses draw very little current.





  • Guaranteed 1% output voltage tolerance (LM317A)
  • Guaranteed max. 0.01%/V line regulation (LM317A)
  • Guaranteed max. 0.3% load regulation (LM117)
  • Guaranteed 1.5A output current
  • Adjustable output down to 1.2V
  • Current limit constant with temperature
  • P + Product Enhancement tested
  • 80 dB ripple rejection
  • Output is short-circuit protected
Output Formula


Once you have learnt enough you can now put the LM317 into use and make the following circuit:

12v Battery Charger Circuit

The circuit may be accustomed charge 12V lead acid batteries.
Pin one of the LM317 IC is that the management pin that is employed to manage the charging voltage, Pin a pair of is that the output at that the charging voltage seems, Pin three is that the input to that the regulated DC offer is given.
The charging voltage and current is controlled by the electronic transistor (Q1), electrical device (R1) and POT (VR1). once the battery is 1st connected to the charging terminals, the present through R1 will increase. This successively will increase the present and voltage from LM317. once the battery is totally charged the charger reduces the charging current and also the battery are charged within the trickle charging mode.

Circuit Diagram



  • The input voltage to the circuit should be a minimum of 3V more than the expected output voltage. luminous flux unit 317 dissipates around 3V throughout its operation. Here I used 18V DC because the input.
  • The charging voltage may be set by victimization the POT (VR1).
  • The luminous flux unit 317 should be mounted on a sink.
  • All capacitors should be rated a minimum of 25V.
  • You'll be able to use crocodilian clips for connecting the battery to the charger.


Source: StreamPowers

Cheap DC Voltage Doubler

This is a cheap DC Voltage Doubler Circuit diagram, which requires a few components and will deliver 10V from a 5V power supply. If the oscillator must be built from a non-functional gate then is required 2 more components: R1 and C3.

The most important parameters of this voltage doubler circuit are given in the table below. Note that because of the IC tolerances these data may have some differences.

Cheap DC Voltage Doubler Circuit Diagram


One Transistor Code Lock Schematic

This is of course the simplest electronic code lock circuit one can make. The circuit uses one transistor, a relay and few passive components. The simplicity does not have any influence on the performance and this circuit works really fine.

One Transistor Code Lock Circuit Schematic

one-transistor-code-lock-Circuit Diagram

The circuit is nothing but a simple transistor switch with a relay at its collector as load. Five switches (S0 to S4) arranged in series with the current limiting resistor R2 is connected across the base of the transistor and positive supply rail. Another five switches (S5 to S9) arranged in parallel is connected across the base of the transistor and ground. The transistor Q1 will be ON and relay will be activated only if all the switches S0 to S4 are ON and S5 to S9 are OFF. Arrange these switches in a shuffled manner on the panel and that it. The relay will be ON only if the switches S0 to S9 are either OFF or ON in the correct combination. The device to be controlled using the lock circuit can be connected through the relay terminals. Transformer T1, bridge D1, capacitor C1 forms the power supply section of the circuit. Diode D2 is a freewheeling diode. Resistor R1 ensures that the transistor Q1 is OFF when there is no connection between its base and positive supply rail.


  • This circuit can be assembled on a Vero board.
  • Switch S1 is the lock’s power switch.
  • The no of switches can be increased to make it hard to guess the combination.
  • Transistor 2N2222 is not very critical here. Any low or medium power NPN transistor will do the job.

220V AC Powered White Led Lamp

This is the simple version of a white LED lamp that can be directly powered from mains. It can give ample light even for reading purpose. Capacitor CX along with diodes D1 through D4 forms the AC step down circuit. CX reduces high voltage AC from mains to a low voltage AC which is rectified by the diodes D1-D4.

220V AC Powered White Led Lamp Circuit Diagram


Capacitor C1 removes ripples from AC so that low voltage DC is available to power the LEDs.CX is the X rated AC capacitor that reduces AC voltage through capacitive rectance property. Resistor R1 is very important to remove the stored voltage from CX when power is switched off. This prevents lethal shock. Resistor R2 limits the inrush current.

More LEDs can be added by reducing the value of R2.Since the circuit is directly connected to mains, take utmost care to avoid shock. No components should be touched when it is connected to mains.

Power Amplifier Using STK3048A for driver input

STK6153 production and use STK3048A amplifier, you reported to have introduced a lot, of which there are many improving circuit, but limited to the STK6153 performance, making the sets of combination play to the top circuit performance is not necessarily the broad masses of Shao You can meet the requirements. In this paper, STK3048A for voltage amplification, Coupled with ultra-dynamic bias circuit at the end of the production of a super-A amplifier.

Power Amplifier Using STK3048A Circuit Schematic 

Power-Amplifier-use-STK3048A-for-driver-input-Circuit Diagram

Below the production elements and brief debugging. Transistor matching error should be 5 percent, the midpoint of migration can be controlled in less than 10 mV. Heat sink should try to get some large, to ensure the safety of power, the general weight of not less than 1,2 kg (two channels), if conditions allow the best and a small 12 V equipment Low Noise fans, for a mandatory cooling. Map k Ω resistance are blocked 0,5 W, Ω block resistance are 1 W, 0,22 Ω resistor is optional 5 W white ceramic resistance. Amp welding after the completion of inspection to correct power debug, W1 decided to amp static bias, the first upward resistance will be transferred to the most, then the smallest amp static bias, access to power, touch all of the phenomenon should be no fever . Potential inspection centres in 10 mV around, gradually changing the resistance W1 (down), so that only 0,22 Ω resistance on both ends voltage of 0,05 V can be, then each of the quiescent current for about 220 mA, and then resume Centre for Migration should be measured in less than 20 mV. W2 resistance decided to "super A" component current size.

For each preference may be, may generally be rotating to the center position value. 10 minutes after the re-testing of the data points can be put into trial if the same sound. As for the effect, to try Pianzhi. Local output power of 70 W +70 W.

Extension for LiPo Charger

Extension for LiPo Charger Project Image


The ‘Simple LiPo Charger’ published in Elektor Electronics April 2005 is a small and handy circuit that allows you to quickly charge two or three LiPo cells. Especially in the model construction world are LiPo batteries used a lot these days, particularly model aeroplanes. It is usual to use a series connection of three cells with these models. Since working with these model aeroplanes usually happens in the field, it would be nice if the batteries could be charged from a car battery. We therefore designed a voltage converter for the LiPo charger concerned, which makes it possible to charge three cells in series. The voltage per cell increases while charging to a value of about 4.2 V, which gives a total voltage of 12.6 V. The converter, therefore, raises the 12-V voltage from the car battery to 16.5 V, from which the LiPo charger can be powered.

Extension for LiPo Charger Circuit Diagram


A step-up controller type MAX1771 in combination with an external FET carries out the voltage conversion. The IC operates at a moderately high switching frequency of up to 300 kHz, which means that quite a small coil can be used.

Because the IC uses pulse frequency modulation (PFM) it combines the advantages of pulse width modulation (high efficiency at high load) with very low internal current consumption (110µA).

The IC is configured here in the so-called non-bootstrapped mode, which means that it is powered from the input voltage (12 V). The output voltage is adjusted with voltage divider R2/R3. This can be set to any required value, provided that the output voltage is greater than the input voltage.

Extension for LiPo Charger PCB Layout

Extension for LiPo Charger-PCB LayOut

Finally, sense resistor R1 determines the maximum output current that the circuit can deliver. With the 25 mΩvalue as indicated, this is 2.5 A.


R1 = 25mΩ(e.g., Digikey # 2FR025-ND)
R2 = 100kΩ
R3 = 10kΩ

C1,C4,C8 = 100nF
C2,C3 = 47µF 25V radial
C5,C7 = 100µF 25V radial
C6 = 100pF

D1 = 31DQ05 (e.g., Digikey #31DQ05-ND)
IC1 = MAX1771-CPA (e.g., Digikey #MAX1771EPA-ND)
T1 = IRFU3708 (e.g., Digikey #IRFU3708-ND)

K1,K2 = 2-way PCB terminal block,lead pitch 5mm
L1 = 47µH high current suppressor
coil, (e.g, Digikey # M9889-ND)
PCB.,ref. 054012-1 from The PCBShop

Author : Unknown - Copyright : Elektor

LED Light Pen Schematic

Physicians and repair engineers often use small light pens for visual examination purposes. Rugged and expensive as these pens may be, their weak point is the bulb, which is a ‘serviceable’ part. In practice, that nearly always equates to ‘expensive’ and / or ‘impossible to find’ when you need one.

LEDs have a much longer life than bulbs and the latest ultra bright white ones also offer higher energy-to-light conversion efficiency. On the down side, LEDs require a small electronic helper circuit called ‘constant-current source’ to get the most out of them. 

LED Light Pen Circuit Diagram


Here, T1 and R1 switch on the LED. R2 acts as a current sensor with T2 shunting off (most of) T1’s base bias current when the voltage developed across R2 exceeds about 0.65 V. The constant current through the white LED is calculated from

R2 = 0.65 / ILED

With some skill the complete circuit can be built such that its size is equal to an AA battery. The four button cells take the place of the other AA battery that used to be inside the light pen.

Author: Myo Min – Copyright: Elektor

Medium-Wave Modulator

If you insist on using a valve radio and listening to medium-wave stations, you have a problem: the existing broadcasters have only a limited number of records. Here there’s only one remedy, which is to build your own medium-wave transmitter. After that, you can play your own CDs via the radio.

The transmitter frequency is stabilised using a 976-kHz ceramic resonator taken from a TV remote control unit. Fine tuning is provided by the trimmer capacitor. If there’s another station in the background, which will probably be weak, you can tune it to a heterodyne null, such as 981 kHz. As an operator of a medium-wave transmitter, that’s your obligation with respect to the frequency allocations. And that’s despite the fact that the range of the transmitter is quite modest. The small ferrite coil in the transmitter couples directly into the ferrite rod antenna in the radio.

Medium-Wave Modulator Circuit Diagram


The modulator is designed as an emitter follower that modulates the supply voltage of the output amplifier. As the medium-wave band is still mono, the two input channels are merged. The potentiometer can be adjusted to obtain the least distortion and the best sound. The RF amplifier stage has intentionally been kept modest to prevent any undesired radiation. The quality of the output signal can also be checked using an oscilloscope. Clean amplitude modulation should be clearly visible.

The medium-wave modulator can simply be placed on top of the radio. A signal from a CD player or other source can be fed in via a cable. Now you have a new, strong station on the radio in the medium-wave band, which is distinguished by good sound quality and the fact that it always plays what you want to hear.


Author: Burkhard Kainka - Copyright: Elektor

White LED Lamp

Did it ever occur to you that an array of white LEDs can be used as a small lamp for the living room? If not, read on. LED lamps are available ready-made, look exactly the same as standard halogen lamps and can be fitted in a standard 230-V light fitting.


We opened one, and as expected, a capacitor has been used to drop the voltage from 230 V to the voltage suitable for the LEDs. This method is cheaper and smaller compared to using a transformer. The lamp uses only 1 watt and therefore also gives off less light than, say, a 20 W halogen lamp. The light is also somewhat bluer.

White LED Lamp Circuit Diagram


The circuit operates in the following manner: C1 behaves as a voltage dropping ‘resistor’ and ensures that the current is not too high (about 12 mA). The bridge rectifier turns the AC voltage into a DC voltage. LEDs can only operate from a DC voltage. They will even fail when the negative voltage is greater then 5 V. The electrolytic capacitor has a double function: it ensures that there is sufficient voltage to light the LEDs when the mains voltage is less than the forward voltage of the LEDs and it takes care of the inrush current peak that occurs when the mains is switched on. This current pulse could otherwise damage the LEDs. Then there is the 560-ohm resistor, it ensures that the cur-rent through the LED is more constant and therefore the light output is more uniform. There is a voltage drop of 6.7 V across the 560-Ωresistor, that is, 12 mA flows through the LEDs. This is a safe value. The total voltage drop across the LEDs is there-fore 15 LEDs times 3 V or about 45 V. The voltage across the electrolytic capacitor is a little more than 52V.

To understand how C1 functions, we can calculate the impedance (that is, resistance to AC voltage) as follows: 1/(2π·f·C), or: 1/(2·3.14·50·220·10-9)=14k4.


When we multiply this with 12 mA, we get a voltage drop across the capacitor of 173 V. This works quite well, since the 173-V capacitor voltage plus the 52-V LED voltage equals 225 V. Close enough to the mains voltage, which is officially 230 V. Moreover, the latter calculation is not very accurate because the mains volt-age is in practice not quite sinusoidal. Furthermore, the mains voltage from which 50-V DC has been removed is far from sinusoidal.

Finally, if you need lots of white LEDs then it is worth considering buying one of these lamps and smashing the bulb with a hammer (with a cloth or bag around the bulb to prevent flying glass!) and salvaging the LEDs from it. This can be much cheaper than buying individual LEDs.


Author: Unknown - Copyright: Elektor

Low Cost Step Down Converter

The circuit described here is mostly aimed at development engineers who are looking for an economical step-down converter which offers a wide input volt-age range. As a rule this type of circuit employs a step-down converter with integrated switching element. However, by using a more discrete solution it is possible to reduce the total cost of the step-down converter, especially when manufacturing in quantity. The TL5001A is a low-cost PWM controller which is ideal for this project.

Low Cost Step Down Converter with Wide Input Voltage Range


The input voltage range for the step-down converter described here is from 8 V to 30 V, with an output voltage of 5 V and a maximum output current of 1.5 A.

When the input voltage is applied the PWM output of IC1 is enabled, taking one end of the voltage divider formed by R1 and R2 to ground potential. The cur-rent through the voltage divider will then be at most 25 mA: this value is obtained by dividing the maximum input voltage (30 V) minus the saturation voltage of the output driver (2 V) by the total resistance of the voltage divider (1.1 kΩ). T1 and T3 together form an NPN/PNP driver stage to charge the gate capacitance of P-channel MOSFET T2 as quickly as possible, and then, at the turn-off point, discharge it again. The base-emitter junction of T3 goes into a conducting state when the PWM output is active and a voltage is dropped across R2. T3 will then also conduct from collector to emitter and the gate capacitance of T2 will be discharged down to about 800 mV. The P-channel MOSFET will then conduct from drain to source. If the open-collector output of the controller is deactivated, a negligibly small current flows through resistor R2 and the base of T1 will be raised to the input voltage level.

The base-emitter junction of T1 will then conduct and the gate capacitance of T2will be charged up to the input voltage level through the collector and emitter ofT1. The P-channel MOSFET will then no longer conduct from drain to source. This driver circuit constructed from discrete components is very fast, giving very quick switch-over times.

Diodes D2 and D3 provide voltage limiting for the P-channel MOSFET, whose maximum gate-source voltage is 20 V. If the Zener voltage of diode D2 is exceeded it starts to conduct; when the forward voltage of diode D3 is also exceeded, the two diodes together clamp the gate-source voltage to approximately 19 V. The switching frequency is set at approximately 100 kHz, which gives a good compromise between efficiency and component size.

Finally, a few notes on component selection. All resistors are 1/16 W, 1 %. Apart from electrolytic C1 all the capacitors are ceramic types. For the two larger values (C2 and C5) the following are used:

  • C2 is a Murata type GRM21BR71C105KA01 ceramic capacitor, 1 µF, 16 V, X7R, 10 %;.
  • C5 is a Murata type GRM32ER60J476ME20 ceramic capacitor, 47 µF, 6.3 V, X5R, 10 %.
  • D1 (Fairchild type MBRS340T3) is a 40 V/3 A Schottky diode. Coil L1 is a Würth WE-PD power choke type 744771147, 47 µH, 2.21 A, 75 mΩ.
  • T1 (BC846) and T3 (BC856) are 60 V, 200 mA, 310 mW complementary bipolar transistors from Vishay.
  • The TL5001AID (IC1) is a low-cost PWM controller with an open-collector output from Texas Instruments.


Author : Dirk Gehrke - Copyright : Elektor

1.5V to 3V Voltage Converter

A simple scheme to generate the inverter voltage from 1.5V to 3V can be made ​​on the basis of slightly modified the well-known multivibrator. Under these denominations in the scheme of the frequency converter is approximately 130 kHz. Inductance value can be calculated or chosen experimentally. But you can simply adjust the frequency of the converter to produce maximum output voltage. Schottky diode VD1 can be replaced by any other similar characteristics.

1.5V to 3V Voltage Converter Circuit Diagram


For further stabilization of the output voltage can be applied to the zener voltage of 3V – 3.3V. This scheme can be used to power a LED or low power devices based on the microcontroller, for example, MSP430.

Parts list :
R1,R3 : 1K
R2 : 2K2
C1 : 470pF
C2 : 100uF/3,3V
C3 : 1000uF
L1 : 470uH
VD1 : 15MQ040
VT1, VT2 : BC547

Piezo Powered Lamp Schematic

Energy is becoming ever more expensive, and some fresh ideas are needed. There are already human-powered devices on the market, most of which employ a dynamo to generate power. It is also possible to recover energy from a piezo crystal of the sort found, for example, in the loudspeakers in greetings cards. Making use of this device is relatively straightforward. 

Piezo Powered Lamp Schematic Circuit Diagram


Piezo crystals can generate voltages of many tens of volts when given a firm enough prod with a finger to bend the baseplate. The charge moved, however,is relatively small and the crystal is effectively a capacitor with a capacitance of only around 20 nF to 50 nF. This means that we need larger-scale storage in the form of an electrolytic capacitor.

The piezo crystal can be treated as an alternating current source. We therefore need a rectifier and a reservoir capacitor. Pressing the metal surface of the transducer ten or twenty times with a finger will charge the electrolytic in steps to the point where it has enough charge to drive a LED. The circuit is a ‘charge pump’ in the full sense of the term.

When the button is pressed the electrolytic discharges into the LED, which emits a brief, but bright, flash of light.


Author :Burkhard Kainka  – Copyright :  Elektor

Converter 12 Vdc to 230 Vac or Inverter

As shown in the Inverter circuit diagram obove , Its used as the oscillator stage astable multivibrator contained in IC1, a CMOS 4047 (this cult series 40xx series) by varying the resistance value of R1 trimmer (220 k total resistance) can vary the oscillation frequency of 40 Hz to 70 Hz square wave, phase shifted by 180 °,  Output pin 10-11 will drives two NPN transistors TR1-TR3, which in turn is fed to the TR2-TR4.

Converter 12 Vdc to 230 Vac or Inverter Schematic

12 Vdc to 230 Vac or Inverter-circuit-diagram

The diodes DS2-DS3, mounted on the output transistors TR2-TR4 are used to protect against voltage surges appearing across the windings V 9 + 9 V transformer T1. For the transformer T1, I used an ordinary mains transformer (primary 230 V so) with a secondary dual 2 x 9 V.


Parts List:
R1 ……. 220 k trimmer
R2 ……. 330 k
R3 ……. 680
R4 ……. 2.2 k
R5 ……. 2.2 k
C1 ……. 4.7 nF polyester
C2 ……. 220 uF electrolytic
DS1 ….. 1N4004
DS2 ….. 1N4004
DS3 ….. 1N4004
DL1 ….. LED
TR1 ….. BC184 NPN
TR2 ….. NPN BDX53C
TR3 ….. BC184 NPN
TR4 ….. NPN BDX53C
IC1 …… 4047 CMOS
T1 …….. transformer sector 80 VA primary 230 V 0.35 A / Secondary 2 x 9 V 3.5 A
S1 ……. switch

Note :

  • Two final power TR2-TR4 should be mounted on the right size heatsink, otherwise they will overheat. You can choose from MJ4033 – MJ3007 or more, provided that the NPN.
  • The maximum power output that can be used depending on the size of the core of the transformer T1, the VA is: with 50 VA can be taken in the secondary 230 V 0.2 A (current consumed by the end will be 4 A) with 90 VA can be taken on the secondary 230 V 0.4 a (current consumed by the end will be 7 A).
  • To power the circuit from the 12V battery, it will take over at least 1.8 millimeters in diameter, to avoid loss by Joule effect.

Auto-off for Audio Gear

A good way to spend a relaxing afternoon is to be in a quiet place with just the right amount of sun or shade, drinks within reach and listening to your favourite songs on MP3 or CD. You doze off and by the time you wake up again the audio equipment has dropped silent due to flat batteries. What a pity!

The simple circuit shown can prevent this embarrassing situation by de-actuating a relay when no audio signal is detected for about two seconds.

Auto-off for Audio Gear Circuit Diagram

Auto-off for Audio Gear-Circuit Diagram

The circuit consists of a sensitive LM358 based comparator, IC1A, which keeps monostable IC2A (a 4538) triggered as long as an audio signal is detected at the input. Via coupling capacitor C1 the circuit takes its input signal from the ‘hot’ side of the loudspeaker or headphones in your audio gear. The monostable will time out 2 s after being triggered, the delay being deter-mined by R6 and C3.

12V DC to 120V AC Inverter

Ever needed a low power 120volt AC  power source for your car, van or truck? Well this circuit should do the trick for you. It will supply 15 watts of AC power to a device. It should power lamps, shavers, small stereos and small appliances. If you draw to much power the circuit will shut down all by itself.

12 Volt DC to 120 Volt AC Inverter Circuit Diagram

12 -Volt DC to 120 -Volt AC-Inverter-Circuit-Diagram

The output of this circuit is a square wave so there may be some noticeable hum on audio units plugged into it. To reduce some of the hum increase the value of the output capacitor which is at .47uf now. That transistor in the circuit are high power PNP transistors. Radio Shack part number 276-2025 are good ones to use or TIP32. The transformer is a 24 volt 2 amp center tapped secondary Radio Shack part number 273-1512 or equivalent.

Simple Light Sensitive Alarm

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

Simple Light Sensitive Alarm Circuit Diagram


The light-sensitivity of the circuit can be adjusted by varying the 100k preset.

The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.