Controlling an esc with PCF8574

Projects General Guidance
1

Hi, i am fairly new to arduino and i'am building a quadcopter with it. It has been a very educational project and i am coming to an end to see my quad flying.

But i've ran into a problem that i am running out of digital pins (analogs are also in use). And i still have 4 esc's to drive.

But luckily i have 2 PCF8574's lying around and esc's are expecting a pwm signal from 1000µs to 2000µs.

I've tried the code as follows but no luck, the three of the esc's are geting around a ~1300µs pulse (don't have an oscilloscope just guessing by motor speed) and one of them doesn't get any signal at all

#include <SPI.h>
#include "nRF24L01.h"
#include "RF24.h"
#include <Wire.h>
#include "PCF8574.h"

#define PCF8574_ADDRESS 0x20

PCF8574 pcf20(PCF8574_ADDRESS);

RF24 radio(9, 10);
const uint64_t pipes[2] = { 0xF0F0F0F0E1LL, 0xF0F0F0F0D2LL };

int throttle = 1000;

void setup() {
  Wire.begin();

  pcf20.begin();
  pcf20.write8(LOW);
  // put your setup code here, to run once:
  Serial.begin(57600);

  radio.begin();
  radio.setRetries(15, 15);
  radio.setAutoAck(false);
  radio.setDataRate(RF24_250KBPS);

  radio.openReadingPipe(1, pipes[1]);
  radio.startListening();
}

void loop() {
  // put your main code here, to run repeatedly:

  while ( radio.available() ) {
    radio.read(&throttle, sizeof(int));
  }
  
  Serial.println(throttle);
  
  
  pcf20.toggle(0); // P0 high
  delayMicroseconds(throttle);
  pcf20.toggle(0); // P0 low
  delay(2);
  
  pcf20.toggle(1); // P1 high
  delayMicroseconds(throttle);
  pcf20.toggle(1); // P1 low
  delay(2);
  
  pcf20.toggle(2); // P2 high
  delayMicroseconds(throttle);
  pcf20.toggle(2); // P2 low
  delay(2);
  
  pcf20.toggle(3); // P3 high
  delayMicroseconds(throttle);
  pcf20.toggle(3); // P3 low
  delay(2);


  //This works fine with digital pins
  /*
  digitalWrite(pwmPin1, HIGH);
  delayMicroseconds(throttle);
  digitalWrite(pwmPin1, LOW);
  delay(2);

  digitalWrite(pwmPin2, HIGH);
  delayMicroseconds(throttle);
  digitalWrite(pwmPin2, LOW);
  delay(2);

  digitalWrite(pwmPin3, HIGH);
  delayMicroseconds(throttle);
  digitalWrite(pwmPin3, LOW);
  delay(2);

  digitalWrite(pwmPin4, HIGH);
  delayMicroseconds(throttle);
  digitalWrite(pwmPin4, LOW);
  delay(2);
  */

}

My question is can you generate a pwm signal with PCF8574?

(Using an arduino uno).

Thanks in advance

2

You /could/ do it, but it would mean that you needed to write to the PCF8574 CONSTANTLY and the Arduino wouldn't have time to do much more else.

You need something like this: Adafruit 16-Channel 12-bit PWM/Servo Shield - I2C interface : ID 1411 : $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits

The chip on the board is actually a LED-driver, but the clever part is that it's PWM-frequency can be set, so it emulates a "servo"-signal (what your ESC needs) and you can control the duty cycle by writing to the registers of it.

// Per.

3

Thank you zapro for your answer. after some research i also realized it was kinda hard and went on bought another arduino uno. Thanks again for your time.