Exposes an AVR atmega8's IO capabilities as an I2C slave. It has:
- 8 analog inputs (8-bit ADC); only 6 with PDIP
- 3 analog outputs (8-bit PWM)
- 8 digital inputs
- 5 (+3) digital outputs
Changes to PWM duty cycles are low-pass filtered; a 0x00 -> 0xff transition needs ~0.13 sec. The PWM outputs can also be used as simple digital outputs.
Digital inputs are debounced (~0.1 sec). The internal pull-up resistors are enabled.
Initial state:
- all digital outputs are low
- all PWM outputs are stopped and low
AVR pin configuration:
- Analog inputs: PC0-PC7 (ADC0-ADC7)
- Analog outputs: PB1-PB3 (OC1A, OC1B, OC2)
- Digital outputs: PB0, PB4-PB7 (+PB1-PB3)
- Digital inputs: PD0-PD7
Needful things:
- build:
make clean && make all - flash:
make program - fuses:
-U lfuse:w:0xe4:m -U hfuse:w:0xd9:m
The default device address is 0x10. You can change it by modifying the I2C_ADDRESS constant in src/potter.c.
The registers are as follows:
| Address | R/W | Description |
|---|---|---|
| 0x00 - 0x07 | R | Analog inputs |
| 0x20 | R | Digital inputs, current state |
| 0x21 | R | Digital inputs, rising edges since last read |
| 0x22 | R | Digital inputs, falling edges since last read |
| 0x40 | W | Analog / PWM output 0 frequency |
| 0x41 | W | Analog / PWM output 0 duty cycle |
| 0x42 | W | Analog / PWM outputs 1 & 2 frequency |
| 0x43 | W | Analog / PWM output 1 duty cycle |
| 0x44 | W | Analog / PWM outputs 1 & 2 frequency |
| 0x45 | W | Analog / PWM output 2 duty cycle |
| 0x60 | W | Bit 0 (LSB): digital output 0 Bits 1-3: PWM0-2 output states when stopped Bits 4-7: digital outputs 1..4 |
Analog / PWM output frequency values:
| Value | Frequency | Notes |
|---|---|---|
| 0x00 | stopped | output is indefinite (high Z) |
| 0x01 | 31250 Hz | - |
| 0x02 | 3906 Hz | - |
| 0x03 | 976 Hz | not supported on PWM1, PWM2 |
| 0x04 | 488 Hz | - |
| 0x05 | 244 Hz | not supported on PWM1, PWM2 |
| 0x06 | 122 Hz | - |
| 0x07 | 30 Hz | - |
MCU peripherals setup:
- ADC prescaling: /64; ADC input clock = 125KHz
- PWM0 = Timer2, PWM1&PWM2 = Timer1
- Timer0 is used as a periodic "tick" interrupt with clk/8 prescale (~3906 tick / second; that is software prescaled by another 2 (~1953 tick))
I2C/TWI slave library comes from here: https://github.com/thegouger/avr-i2c-slave; thank you!
- make the pwm "lpf" configurable
- externalize I2C_ADDRESS to a build variable
- clean up the code, it's plain disgusting