Question about usage of 4-Channel PCA9536

anthonycalderone · August 30, 2019, 12:38am

Hi Everyone,

I’m a new user to NCD products. I bought two products from NCD, the 4-Channel I2C PCA9536 Optical Isolated Digital Input with I2C Interface and the Analog Devices AD5254 Digital Potentiometer 4-Channel 256-Position I2C Mini Module. I got the DigiPot setup in Arduino and running perfect in 30 minutes. Then I came to the Optical Isolated GPIO and I’m banging my head against the wall. I’ll explain what I’m trying to do because I’m think I might be misunderstanding what the GPIO board can do.

I am trying to emulate 4 button presses with my Arduino and for this discussion we only need to pretend I’m controlling 1 button. Before I bought the NCD board, I bought a PC817 Optocoupler and used a breadboard to test out my “button pressing”. My button has 3V going through it. So I was able to send 5V to my optocoupler (through Pin 1 & 2 on PC817) and this closed the circuit on my 3V button (through Pin 3 & 4).

This led me to buy the 4 Channel GPIO as it seemed exactly what I needed to. In fairness I am quite new to electronics, as this is a hobby for me and my son. I am C++ developer and I can say I am humbled every time I tackle a new electronics project because I realize there is so much I don’t know.

Question 1: Is this GPIO board the correct device for having the Arduino activating the optocouplers in this board, so I can emulate my button presses?

Question 2: If so, are there any code examples in Arduino to activate each channel? I have searched google and found libraries for controlling the PCA9536. I have used straight code using <wire.h>, just as I use the DigiPot. Nothing I do in the code activates/deactivates the channels on the GPIO board. I have my 3V button line on “IN1” on the board and I have my volt meter across the terminals. I always read 3V (I expect when I set LOW, it should break the circuit and I should read 0V). I downloaded and tried the <SparkFun_PCA9536_Arduino_Library.h> and nothing.

Thanks for any help!
Anthony

Bhaskar · August 30, 2019, 12:45am

Hi Anthony,
This is how the button needs to connect.

Button’s one end to IO1 screw terminal “+”
Button’s other end to 3.3V
IO1’s other screw terminal “-” to ground

here is a sample code you can use

github.com

ControlEverythingCommunity/PCA9536/blob/master/Arduino/PCA9536.ino

// Distributed with a free-will license.
// Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
// PCA9536
// This code is designed to work with the PCA9536_I2CIO I2C Mini Module available from ControlEverything.com.
// https://www.controleverything.com/content/Digital-IO?sku=PCA9536_I2CIO#tabs-0-product_tabset-2

#include <Wire.h>

// PCA9536 I2C address is 0x41(65)
#define Addr 0x41

void setup()
{
  // Initialise I2C communication as Master
  Wire.begin();
  // Initialise serial communication, set baud rate = 9600
  Serial.begin(9600);

  // Start I2C transmission
  Wire.beginTransmission(Addr);

This file has been truncated. show original

Let me know if you run into any issues.

Thanks

anthonycalderone · August 30, 2019, 3:11am

Hi Bashkar,

I figured out the Arduino code to set the states to HIGH and LOW.
However, I did not notice a change in the output.

When I reread you comment, I thought I might have confused you with talk of the button.
I made a little schematic of what I actually have.
There is “no button” on my device, just a 3.5mm plug with ground and 3V.
When I touch the two contacts together, my device registers a “button push”. (Technically it registers button push when you disconnect the two contacts).
Basically I need a switch and I know I could have used an electromagnetic relay, but this is low voltage and very low current.
So I assumed clicking electromagnetic relay would be slow and overkill for this.

I am attaching a picture of my schematic and a real picture of the plug connected to the board.

Bhaskar · August 30, 2019, 2:47pm

Hi Anthony,
The board is an Input board. It will not be able to set outputs high and low.

if you just want to set high and low i will recommend a general purpose IO board. like this one

it has 4 relays and 4 io. You can use either one.

Thanks

anthonycalderone · August 30, 2019, 3:03pm

Thanks!
I had a feeling this might have been an “input only board”, but I was bit confused by the name of “GPIO”.
This is my in experience with electronics