I recently purchased a Turnigy 9x transmitter from Hobby King, with the full intention of upgrading the firmware. I had know (or thought) that it was possible to program AVR's using an arduino as the programmer, and being a cheapskate, I didn't bother to purchase one of the recommended programmers. I figured many people must have already done this and there would be some good guides out there. Well, I was wrong. There are some excellent guides on programming the radio with standard hardware, but none using the arduino. That's where this guide comes in. It's meant as a supplement to other guides.
Turn your arduino into an AVRISP programmer
This one is pretty simple. Go to the arduino software, and find the example “arduinoISP”. Open the sketch and upload it to your arduino. See the arduino page for more info.
Attach cable to TX
Open your transmitter, and identify the solder points. There are six of them, and you can refer to other guides if you are unsure. I used a 5S1P lipo connector because it has 6 conductors and I had one lying around. It works pretty slick. I didn't bother to label anything at this point. Just soldered one wire to each point.
Attach test leads
On the other end of the cable, plug in the male portion of the plug with bare pins on the back side. Cut 3 test leads in half and soldered all six pieces to each of the six bare posts. Now with a multimeter, match-up and label each test lead with its corresponding point on the PCB. Label them according to this picture.
Connect all the test leads to the arduino using the pin assignments from the sketch. It should be as follows:
// 10: slave reset
// 11: MOSI
// 12: MISO
// 13: SCK
Connect the gnd and +5V to the power block on the arduino, and tripe check that you have the polarity correct.
Disable auto reset
Some arduinos (including my Duemilanove) have an auto reset function that needs to be disabled. To do this, place a 120 Ohm resistor between +5 and reset. The instructions are here.
In the eePe software, burn->configure and select the AVRISP programmer from the list. Assuming your radio is like mine, set the processor to m64, and set your port to whatever your arduino uses. In the extra arguments line, put “-b 19200”
Program the radio
You should be good to go. Follow the other guides for programming from here. I suggest you back-up your flash memory first, and all that.