Simple USB AVR-ISP Compatible Programmer

Modern PCs rarely have a serial or parallel  port any more, to the great regret of any-one who experiments with microcontrollers every now and then. In the old days  it was very simple to use the parallel port  of a standard PC and program just about  any type of AVR microcontroller with it.  When you want to do that now, you’re first  obliged to buy a programmer that communicates with the PC via USB, which immediately raises the threshold of getting started  with these microcontrollers. The circuit presented here offers a solution to this.

Simple USB AVR-ISP Compatible Programmer Circuit Diagram :

Simple USB AVR-ISP Compatible-Programmer-Circuit Diagram

As you can see from the schematic, this is  a very simple circuit, built around a cheap,  standard AVR microcontroller plus a handful of passive components. You may have  already observed that this microcontroller does not have a USB interface and the  circuit does not use a USB to serial converter either. The strength of this circuit is  found in the firmware. The USB interface  has been implemented in software, as we  have shown in an earlier article ‘AVR drives  USB’ in the March 2007 issue. The firmware  ensures that the circuit is recognised by the  PC as a serial port and communicates with  AVR Studio, the standard Atmel development environment, as if it were a ‘real’ AVR-ISP programmer.

The circuit is easily built on a small piece  of prototyping board or even on a bread board, since the controller is available in  a DIP-28 package. If you are going to pro-gram the controller yourself (via connector K2) then make sure that you set the  configuration fuses so that the internal  oscillator uses the external crystal as the  clock source.

Jumper K3 is provided in the event you would like to power the circuit to be programmed from the USB port. We do not  recommend that you do this, however,  but sometimes there is no other option.  K4 is a 10-way box header which has the  same standard pinout that Atmel uses  everywhere.

Author : Nand Eeckhout - Copyright : Elektor

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