MCP41100 (digital Pot) does not show correct value

arunb · Joined: 08 Sep 2003 Posts: 492 Location: India

PCM 3.169
MCU 16F628

Hi,

I am using a 16F628 mcu to control a MCP41100 (100 K digital pot).

After powering up the device, I checked the resistance between the PB0 and PA0 (resistor ends) and found that it was 72 Kohm instead of 100Kohm.

Kindly explain this anamoly.

thanks
arunb

dyeatman · Joined: 06 Sep 2003 Posts: 1933 Location: Norman, OK

I might suggest you read the device data sheet particularly paying attention to the section on the 100K version. I believe that will povide the explanation you require.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

Every part that is manufactured has a 'tolerance' associated with it since nothing is perfect. There should always be a plus/minus associated with it. The spec. sheet states that, for the 100K version, the internal resistance is 100K plus/minus 30K. It's a rather wide window but it's what is spec'd out and your part falls, barely, within that specification. The only way to get a 100K part is to buy a bunch of them and measure each one until you find one that is close enough.

Ronald

Ttelmah · Guest

Also, remember that if there is any load on the wiper, this will affect the apparent resistance between the endpoints.

Best Wishes

arunb · Joined: 08 Sep 2003 Posts: 492 Location: India

Hi All,

Thanks for the help.

bye
arunb