Problem with interfacing MCP4651-502E digital potentiometer using I2C

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1

Hello everyone,

i am using two MCP4651 dual digital potentiometers, i also attached PCB schematic, which i want to control from arduino uno thru I2C. Here's datasheet for MCP4651, so you don't have to look for it: http://www.farnell.com/datasheets/1789212.pdf

I am trying to write my value into the wiper 1 register like on page 49 of datasheet. But every command i try, i get not acknowledged. I also attached screenshot of oscilloscope.

Here's my code:

#include <Wire.h>

void setup() 
{
  Wire.begin();
}

void loop()
{
  Wire.beginTransmission(40);
  Wire.write(0b10010000);
  Wire.write(0b10000000); 
  Wire.endTransmission(40);
  delayMicroseconds(500);
}

The I2C protocol clearly works, or i would not get acknowledged address and i tried both potentiometers, both wipers, writing, incrementing and decrementing. Not a single success. If anyone knows what am i doing wrong, i would be grateful.

schematic.PNG
schematic.PNG860×436 4.96 KB

2

Here's the screenshot, it was too big for upload

3

Address 40 means all A0,A1,A4 grounded.
pullup_resistors missing ?? scope shows 3.6V Should be closer to 5V ?

Move 4 code_lines (transmission) to setup(). (Why repeat write unaltered data?)

How do you know that the viper isn't set correctly?

4

Yep, addresses are 40 and 41.
There are 2k7 pullup resistors, it can operate between 1.8V and 5.5V so i chose 3.3V.
I have it in loop cos i was incrementing the wiper before, forgot to move it in setup after.

Well for MCP46XX you need to send 3 bytes : address, command and value, and you can see in the scope that address was sent OK, it acknowledged, but after the command was sent, it did not acknowledge. Also i was measuring that wiper, and it was constant.