168 LED PWM controller
168 : LED PWM controller
- Author: Mikkel Holm Olsen
- Description: Exponential LED PWM controller
- GitHub repository
- Clock: 32768000 Hz
How it works
This is an 8-channel PWM controller for LED brightness.
The PWM duty cycle is generated according to an X<sup>3</sup> curve, so the "percieved brightness" changes linearly with the register setting. This design means we get the dynamic range of a 16-bit PWM but use only 8 bits to specify the desired output. With an input clock of 32.7 MHz, the PWM frequency is 500 Hz.
After reset, the controller is in UI mode, where the ui[7:0] set the 8 PWM value registers. The first PWM value register is set to ui[7:0], for the remaining PWM value registers they are set to 0 when ui[7:0] == 0, but in other cases their value is ui[7:0] XOR X, where X is 0x10 times the register number.
The individual registers can be accessed by I2C; SCL=UIO2, SDA=UIO1, which should allow accessing it from the Rpi2040 on the demo board. The slave address is 0x6C, and the 8 PWM channels are controlled by register addresses 0 thru 7. As soon as the first I2C write occurs, the controller is set to I2C mode, and the ui inputs no longer affect the registers.
How to test
Play with the DIP-switches to see different segments of the 7-segment LED display show different brightnesses.
External hardware
Currently no external hardware is supported.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | duty[0] | PWM channel 0 | |
| 1 | duty[1] | PWM channel 1 | SDA |
| 2 | duty[2] | PWM channel 2 | SCL |
| 3 | duty[3] | PWM channel 3 | |
| 4 | duty[4] | PWM channel 4 | |
| 5 | duty[5] | PWM channel 5 | |
| 6 | duty[6] | PWM channel 6 | |
| 7 | duty[7] | PWM channel 7 |