AD5254 100K Resistance help

nick.lestician · July 11, 2020, 12:00am

Hi there,

I purchased a 4 channel digital pot from ncd that is 100k value, and I used this script linked below and the max resistance I can get out of the pot is 5K based on the script, I need to be able to go up to 60k, and I have tried researching the chip for the registers but I cannot find anything on changing the resistance values.

I can go from 5K down to .09K which is fine for my other applications, but I need to go up right now for my current application.

github.com

ControlEverythingCommunity/AD5254/blob/master/Python/AD5254.py

# 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.
# AD5254
# This code is designed to work with the AD5254_I2CPOT_10K I2C Mini Module available from ControlEverything.com.
# https://www.controleverything.com/content/Potentiometers?sku=AD5254_I2CPOT_10K#tabs-0-product_tabset-2

import smbus
import time

# Get I2C bus
bus = smbus.SMBus(1)

# AD5254 address, 0x2C(44)
# Send instruction for POT channel-0, 0x00(00)
#		0x80(128)	Input resistance value
bus.write_i2c_block_data(0x2C, 0x00, [0x80])
# AD5254 address, 0x2C(44)
# Send instruction for POT channel-1, 0x01(01)
#		0x80(128)	Input resistance value
bus.write_i2c_block_data(0x2C, 0x01, [0x80])

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Any help would be appreciated where I am going wrong or missing something.

https://store.ncd.io/product/analog-devices-ad5254-digital-potentiometer-4-channel-256-position-i2c-mini-module/

This is the pot I purchased.

Bhaskar · July 11, 2020, 2:02am

Hi,
can you share a close up picture of the POT IC on the board ?

Thanks

nick.lestician · July 11, 2020, 6:28am

Hi there,

Here is the closeup of the IC. I made sure it was the 100K version of the chip when I ordered it. I do have a few other devices on here as you can see on the second photo, and I made sure to have the pull up resistor on the first board on.

Please let me know if you need anything else.

nick.lestician · July 12, 2020, 3:31am

Any solution for this? @Bhaskar

Basically from what I see is when I write 0x80 it gives a resistance of 5K, 0x40 gives a resistance of 2.5K. Going higher than 0x80 does not increase the resistance from my tests.

Bhaskar · July 12, 2020, 3:56am

Hi Nick,
It is a 100K pot ( the 100 marking on the IC).

I dont have one of these to test. I will see if i can get one for testing early next week.

meanwhile Try this lib

github.com

ncdcommunity/Raspberry_Pi_AD5254_4Channel_Potentiometer_Sensor_Python_library/blob/master/AD5254.py

# 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.
# AD5254
# This code is designed to work with the AD5254_I2CPOT_10K I2C Mini Module available from ControlEverything.com.
# https://www.controleverything.com/content/Potentiometers?sku=AD5254_I2CPOT_10K#tabs-0-product_tabset-2

import smbus
import time

# Get I2C bus
bus = smbus.SMBus(1)

# I2C address of the device
AD5254_DEFAULT_ADDRESS				= 0x2C

# AD5254 Command Set
AD5254_WORD_RDAC0_EEMEM0			= 0x00 # Store RDAC0 setting to EEMEM0
AD5254_WORD_RDAC1_EEMEM1			= 0x01 # Store RDAC1 setting to EEMEM1
AD5254_WORD_RDAC2_EEMEM2			= 0x02 # Store RDAC2 setting to EEMEM2
AD5254_WORD_RDAC3_EEMEM3			= 0x03 # Store RDAC3 setting to EEMEM3

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Thanks

nick.lestician · July 12, 2020, 4:52am

Hi, thanks for the reply.

The script comes back with a syntax error.

Traceback (most recent call last):
File “/home/pi/Desktop/4.py”, line 88
print “Resistance at WB: %.2f K”%(res[‘b’])
^
SyntaxError: invalid syntax

I am using Thonny on the raspberry.

I changed some parameters around and got it to work, but the resistance values from what I see are not right. I will check later today when I am there to measure the resistance and see if does what I want it to do. Please do let me know if there is something on the script that I need to fix to make it work.

Thanks

nick.lestician · July 13, 2020, 7:09pm

@Bhaskar I just tried it on the Arduino with the i2c and it shorted the chip when I ran the arduino script from github. When you get the piece this week please test it on raspberry, because that is my main application. Its not changing anything on the pot with the script you linked. Thankfully I bought 2 of the same pot to use.

Bhaskar · July 15, 2020, 1:46pm

I should receive one tomorrow for testing.

Bhaskar · July 17, 2020, 2:05am

i will recommend this

no code running in pi
disconnect AD5254
connect AD5254

measure resistance across A and W. it should be 50K

I tested with arduino and my test code looks like this
#include<Wire.h>

// AD5254 I2C address is 0x2C(44)
#define Addr 0x2C

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);
// Send instruction for POT channel-0
Wire.write(0x00);
// Input resistance value, 0x80(128)
Wire.write(0x80);
// Stop I2C transmission
Wire.endTransmission();
}
void loop()
{
for(int i = 0; i <256; i++)
{
// Start I2C transmission
Wire.beginTransmission(Addr);
// Select data register
Wire.write(0x00);
Wire.write(i);
// Stop I2C transmission
Wire.endTransmission();
Serial.print(“Resistance Channel-0 : “);
Serial.print(i);
Serial.println(” K”);
delay(500);
}
}