This serial port AVR programmer (DASA) uses the host computer's serial port to create an SPI link to the AVR
microcontroller. The programmer may be built in the serial port connector's headshell, or in a box. It can
even be encapsulated in epoxy or covered with heatshrink tubing somewhere in the serial cable. There are
a few other serial AVR programmers listed on the Programmers page
Schematic Diagram
Parts
R1-R3 4.7k 5% 1/8W resistor
D1-D3 5.1V 1W zener
X1 DB9S solder cup connector
Not shown
Perfboard
DB9 headshell
6 or 10 conductor ribbon cable
6 or 10 conductor ribbon connector
Notes
The target AVR microcontroller must provide it's own power.
Each resistor/zener pair implements a clamp to hold the applied voltage to between -0.6 and +5.1 V.
The RTS signal holds reset low while programming.
CTS, TXD, and DTR form an SPI interface to program the chip.
Assembly
This is a simple circuit, and it could have been done using discrete wiring, but I chose to use a tiny piece of
perfboard that fits inside the headshell. I soldered pins 6 - 9 to the board pads for a little structural
integrity. The resistors and diodes all line up to make the backside wiring simple and clean.
It makes sense in this application to use a strain relief on the cable, since you will be tugging on it often.
