Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface

[espruino-discuss2]

Posted at 2018-12-07 by Matteo

Hi!

Sorry for the question, I'm a kind of newbie...

I was wondering if it's possible to connect Espruino Wi-Fi to the Adafruit 16-Channel 12-bit PWM/Servo Shield (https://learn.adafruit.com/adafruit-16-channel-pwm-slash-servo-shield/overview).

And, if it is, how to program it?
Should I connect the SDA and SCL pins on the boards and use a code similar to this: https://www.espruino.com/arduino-motorshield?

Thank you!

[gfwilliams]

Posted at 2018-12-10 by @gfwilliams

Hey, no problem! Yes, it is possible to use it - I believe just connecting, GND, power, SDA and SCL would be enough.

However it's not entirely simple as we don't currently have a library for the PCA9685 chip - so you'd have to send the I2C commands needed to control it using Adafruit's code (https://github.com/adafruit/Adafruit-PWM-Servo-Driver-Library/blob/master/Adafruit_PWMServoDriver.cpp) as a base.

I can definitely help you to do that if you want (and I'm happy to make a library so that it is really easy to use code with it), but I don't have a PCA9685-based board here so it might require a little bit of trial and error!

I should add that if you just want to control servos, you can just connect them straight to the Espruino WiFi - you should be able to control quite a few of them at a time without issues.

[espruino-discuss2]

Posted at 2018-12-10 by Matteo

Thank you for your kind reply, Gordon! :-)

I am a frontend web developer (that's why I love Espruino), but as I said I am a newbie in electronics, hence I am not sure to be able to do what you are suggesting.

I know I can control servos directly from Espruino (already successfully done!), but I am trying to learn something new reusing hardware from previous experiments with different microcontrollers.

By the way, I would like to try to "translate" Adafruit c++ code to a module for Espruino, avoiding to bother you with my personal experiments! ;-)
Could you please suggest me a way to start? Maybe the code of another module you already ported into js for Espruino?

I definitely wanna deepen this stuff. Maybe the libs/README.md file (https://github.com/espruino/Espruino/blob/master/libs/README.md) could be a starting point.

[gfwilliams]

Posted at 2018-12-10 by @gfwilliams

Great! In this case you should be able to do what you want in normal JavaScript, so actually delving into Espruino itself isn't needed - maybe that link should mention it?

What you really need is: http://www.espruino.com/Writing+Modules

The modules that use I2c (http://www.espruino.com/I2C#using-i2c) are a good start - and the code for them is usually here: https://github.com/espruino/EspruinoDocs/tree/master/devices

To get you started, just copy/paste this into the Web IDE:

Modules.addCached("pca9685_servo",function() {
var C = {
PCA9685_SUBADR1 : 0x2,
PCA9685_SUBADR2 : 0x3,
PCA9685_SUBADR3 : 0x4,
PCA9685_MODE1 : 0x0,
PCA9685_PRESCALE : 0xFE,
LED0_ON_L : 0x6,
LED0_ON_H : 0x7,
LED0_OFF_L : 0x8,
LED0_OFF_H : 0x9,
ALLLED_ON_L : 0xFA,
ALLLED_ON_H : 0xFB,
ALLLED_OFF_L : 0xFC,
ALLLED_OFF_H : 0xFD
};
function PWMServoDriver(i2c) {
  this.i2c = i2c;
  this.addr = 0x40;  
  this.reset(()=>{
    this.setPWMFreq(1000);
  });
}
PWMServoDriver.prototype.write = function(r,d) {
  this.i2c.writeTo(this.addr,r,d);
};
PWMServoDriver.prototype.read = function(r) {
  this.i2c.writeTo(this.addr,r);
  return this.i2c.readFrom(this.addr,1)[0];
};
PWMServoDriver.prototype.reset = function(callback) {
  this.write(C.PCA9685_MODE1, 0x80);
  if (callback) setTimeout(callback,10);
};
PWMServoDriver.prototype.setPWM = function(num,on,off) {
  this.i2c.writeTo(this.addr,
                   C.LED0_ON_L+4*num,
                   on, on>>8,
                   off,off>>8 );
};
PWMServoDriver.prototype.setPWMFreq = function(freq) {
 // FIXME
};
exports.connect = function(i2c) {
  return new PWMServoDriver(i2c);
};
});

var i2c = new I2C(); // software I2C
i2c.setup({sda:SDA_PIN, scl:SCL_PIN});
var servo = require("pca9685_servo").connect(i2c);

So you need to implement setPWMFreq, but the general outline of what you need should be there for the other stuff. I did setPWM because Espruino can do it a bit more tidily than Arduino can.

Other thing to note is that servos don't run at 1000Hz (the default) so you have to use Adafruit's example: https://github.com/adafruit/Adafruit-PWM-Servo-Driver-Library/blob/master/examples/servo/servo.ino

Part of me thinks it's worth just setting it to 60Hz by default and adding a 'setServo' function as well though. Most people are going to use this board/chip for servos anyway :)

[espruino-discuss2]

Posted at 2018-12-11 by Matteo

Wow! A lot of stuff here! :-)
Thank you a lot... I will try to use it!

[espruino-discuss2]

Posted at 2018-12-11 by Wilberforce

Moduled.addCached("pca9685_servo",function()
Should that be:

Modules.addCached("pca9685_servo",function()

[gfwilliams]

Posted at 2018-12-11 by @gfwilliams

Thanks - just fixed! And I spotted some other issues too - I should have tested that!