Electronics -- Atmel/AVR-programming: Supply Circuit
Please note that I am now using the USB-based download cable. Content on this page is no longer maintained/developed. However, the presented solution is cheap, easy to build and still working nicely.
AVR RISC Programmer: Supply Circuit
NOTE: This circuit was primarily designed to allow parallel downloading which requires that 12V be applied to the RESET line of the AVR RISC to be programmed. Although you do not need the 12V part for serial downloading (in-system programming), you can still use this device (as I did as well) but make sure not to switch S2 to the "Prog" side; serial downloading must be done while S2 is in "Reset" state.
This is the Atmel programmer supply and reset logic circuit as used by me for more than a year. You only need a stabilized 12V supply (11.5-12.5V) as the design applies an uA7805 (5V, 1A voltage regulator) for the 5V logic level supply.
The design includes a single switch which allowes you to choose between the Atmel microcontroller's operation modes "reset/serial programming " (0V at RESET pin), "parallel programming" (12V), and "run" (5V).
Download Atmel programmer supply electronic circuit sheet:
The Technical Details
Here is the circuit. The JP1 on the left is to be connected to a stabilized 12V source, JP7,JP8 indicate power and programming mode, respectively and are to be connected to pin 2 and pin 4 of the Latch16Bit STATUS/INB port (see the programmer circuit). The micocontroller's VCC, GND and RESET are plugged in at JP6. JP2-5 are 5V supply outputs for other devices.
This circuit is a bit tricky as of the timing: Assume that S2 is in middle state, i.e. "Reset". Upon power up, C3, C4 and C5 have no voltage and hence, IC3A,B's outputs are both high and IC3C's one is LOW. Due to the chosen capacity and resistor (R3, R4, R6) values, IC3B goes low fitst, followed by IC3A (approx. 10ms) and finally IC3C goes high (approx. 80ms after power up). This means, that the CD4052 analog multiplexer connects in this order X3,X1 and X0 with the reset line. Hence, reset stays at 0V during power up keeping the microcontroller in "reset" mode.
The rest is fairly easy: C3,4 together with R1,3,4 are used to debounce the switch S2. Depening on whether you flip S2 into "Prog" or "Run" mode, IC2 connects 5V or 12V to to the reset line.