This is a basic firmware for the cheap USB relay boards that are sold on eBay and report themselves as being from www.dcttech.com. They're based on an Atmel ATtiny chip and run V-USB as the core of their firmware.
This project deviates from the basic firmware in 2 ways.
- Implement reading the serial number from the eeprom area.
- Added a watchdog timer
The HID driver sends a byte array to the device. Use the first byte to control the state of the relay, byte[0]=0 de-energize and byte[0]=1 energize. The second byte enables a watchdog timer count down with the value in seconds, byte[1]=5 would time out after approximately 5 seconds. The relay opens when decrementing to zero so if you leave the timer at zero it is effectively disabled.
apt install avr-libc avrdude should install the appropriate build requirements on Debian (gcc-avr will be automatically pulled in) assuming you already have build-essential installed for make.
make will then build you a main.hex which you can program to your device using
avrdude. With my cheap USBASP I use:
avrdude -P /dev/ttyUSB0 -c usbasp -p t45 -U flash:w:main.elf:e
Pin outs on the 1 port relay board look like:
|RELAY|
+-----+ [USBASP connections]
o RESET RST
o SCK CLK
+--+ o MISO MISO
|AT| □ MOSI MOSI
+--+
□ 5V +5V
o GND GND
| USB |
+-----+
USB D- is connected to Port B pin 1, USB D+ to Port B pin 2 (INT0) and the relay is hanging off Port B pin 3.
Given that V-USB is GPLv2+ or commercial all of my code is released as GPLv3+, available at https://the.earth.li/gitweb/?p=usb-relay-firmware.git;a=summary or on GitHub for easy whatever at https://github.com/u1f35c/usb-relay-firmware