Using the example, resistance is set to half of the wanted value

[bennigraf]

Hi there!

I just tried to use this library and got it basically working with a 4261 (two channel, 8 bit, 100kOhm). But when I run the example, instead of going from 0 to 100k in 20k-steps, it goes from 0 to 50k in 10k steps (half of the wanted values).

Except for creating the instance with 100k I have nothing else changed in the example.

Setting digitalPot.scale to 50 fixes the behaviour and outputs the wanted value (0 to 100k).

I also tried the "original" class (https://github.com/dreamcat4/Mcp4261) and with that it works as expected.

No urgent fix needed as I can work around that, I just wanted to file the bug report ;-). Thanks for your time!

Best,
Benni.

[dl111122]

It appears to me the problem is in line 54 of McpDigitalPot.h where it has
const static unsigned int resolution = resolution_7bit;
Some chips in this family have 128 bit (7bit) resolution, and some have 256 bit (8bit resolution).
The 4261 chip has 8 bit resolution. So changing that line to:
const static unsigned int resolution = resolution_8bit;
fixes the problem for the 4261 chip.

The comments says look at the 3rd digit of the model i.e. MCP4-N-
where if N=3 7bit volatile
if N=4 7bit non-volatile
if N=5 8bit volatile
if N=6 8bit non-volatile
For a 4261, N=6, means it should be 8bit.