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Measure resistance on DS3502
Moderators: adafruit_support_bill, adafruit

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Measure resistance on DS3502

by amahpour on Mon Dec 06, 2021 4:27 pm

Hi,

I purchased the DS3502 breakout board and followed the guide on how to hook it up with my Raspberry Pi (https://learn.adafruit.com/ds3502-i2c-potentiometer/).

When I go to measure the resistance between RW and RH or RL I don't see anything change (i.e. it's constant at 0 ohm or some high value in the megaohm range). I disconnected the voltage connections (to achieve a resistor divider as instructed in the tutorial) as well but that made no difference. I am able to measure the 10k ohms across RH and RL just fine.

Am I using this chip incorrectly? My objective was just to create some sort of variable resistor.

Thanks,
Ari

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Re: Measure resistance on DS3502

by adafruit_support_carter on Mon Dec 06, 2021 6:57 pm

What is your specific end use for the variable resistor? Something other than a variable voltage divider?

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Re: Measure resistance on DS3502

by adafruit_support_bill on Mon Dec 06, 2021 7:52 pm

Do you have a voltage connected across RH and RL?

See this thread on the topic: viewtopic.php?f=8&t=182498&p=887476

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Re: Measure resistance on DS3502

by amahpour on Mon Dec 06, 2021 8:57 pm

I'm literally looking to output a resistance to test a DMM (in resistance mode). I do NOT want to have any voltage applied to the output because the DMM will be sourcing its own current and voltage. Can this chip do that? If not, do you have any other recommendations?

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Re: Measure resistance on DS3502

by adafruit_support_bill on Mon Dec 06, 2021 9:10 pm

It doesn't look like you need a voltage on the output, but you do need a voltage on the V+ pin which is connected by default to VH. V+ needs to be 4.5v minimum. See the guide and datasheet for other constraints..

https://learn.adafruit.com/ds3502-i2c-p ... -3035907-4
https://datasheets.maximintegrated.com/en/ds/DS3502.pdf

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Re: Measure resistance on DS3502

by amahpour on Tue Dec 07, 2021 7:37 pm

Awesome. That worked! Thank you so much.

The only thing I am noticing is that reading across RL and RW with my DMM results in:
0 --> 4.1 kOhm
63 --> 8.65 kOhm
127 --> 14.08 kOhm

Is there a way to set this to go even lower? Like in the single digits Ohms range as I get closer to 0?

Thanks.

amahpour
 
Posts: 108
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Re: Measure resistance on DS3502

by adafruit_support_bill on Tue Dec 07, 2021 9:33 pm

I don't think so. The resolution is only 128 steps. And according to the datasheet, there is some resistance across the wiper as well (5K @15V)

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Re: Measure resistance on DS3502

by amahpour on Tue Dec 07, 2021 9:54 pm

Bummer. Know of any other "Digital POTS" that will get me a range of 1 ohm to 4k Ohm (i.e. what I'm missing from the DS3502)?

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Re: Measure resistance on DS3502

by adafruit_support_bill on Wed Dec 08, 2021 7:15 am

I don't know if there are any that will get you to 1 ohm resolution. But it looks like Analog has some that will get you down to 4 ohms (256 steps over 1K)
https://www.analog.com/en/parametricsea ... |1%20kOhms

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