Putting device requiring 500k potentiometer under micro control - Page 1
Forum section: electronics / projects

author: plantgrower
author_rank: Contributor
timestamp: March 25, 2013, 06:10:14 pm
content: How do I replace a 500k potentiometer that controls a device wtih something able to be controlled by a micro ?

author: kfitch42
author_rank: Frequent Contributor
timestamp: March 25, 2013, 06:15:28 pm
content: http://www.digikey.com/product-search/en/integrated-circuits-ics/data-acquisition-digital-potentiometersLooks like you could use to 250K digital pots in series or use a 1M digital pot, but only use half the range.The other possibility is to figure out what the 500k pot is accomplishing. Often it is used as a voltage divider. So you can figure out what voltage the device gets at various positions of the pot, and use a micro to program a DAC to generate the proper voltage range. if the range of the device doesn't overlap with the range the micro can generate you may need to use a simple op-amp circuit (see one of Dave's t-shirtsto adjust the range output by the micro to the range the device wants.

author: firewalker
author_rank: Super Contributor
timestamp: March 25, 2013, 06:18:31 pm
content: If the pot only controls a dc voltage you could possibly replace it with a filtered PWM. You really must provide more infos.Alexander.

author: c4757p
author_rank: Super Contributor
timestamp: March 25, 2013, 06:18:36 pm
content: What is the device? Lots of things use a potentiometer but don't truly require one.

author: mariush
author_rank: Super Contributor
timestamp: March 25, 2013, 06:19:33 pm
content: There are digital potentiometers you can use with a microcontroller (through serial, i2c, up/down signals, one-wire etc). Most are up to 100kOhm though, but nothing says you couldn't chain 5 of them.Otherwise, depending on what that resistor is used for, or how it is in circuit, you may be able to replace it with a DAC ic (your micronctroller uses a value between 0 and 1023 to output a voltage between 0-5v or something like that, which you can then further adjust with opamps or whatever)Or if you don't need fine grained adjustments, even a bunch of solid state relays/classic relays or npn transistors/mosfets would work to add or remove resistors to a series of resistors .. let's say 10 x 50k resistors.

author: plantgrower
author_rank: Contributor
timestamp: March 25, 2013, 06:41:06 pm
content: The device to be controlled ishttp://www.kemo-electronic.de/en/Transformer-Dimmer/Controller/Modules/M050-Transformer-control.php

author: mariush
author_rank: Super Contributor
timestamp: March 25, 2013, 06:58:55 pm
content: You'll have to open it up and see how is that potentiometer connected.Often, the potentiometer is just one resistor of the two resitors that form of voltage divider :So in this case, the circuit inside receives that voltage coming out from the voltage divider and adjusts the power accordingly. Therefore, you could just remove the potentiometer and the other resistor and just send the expected voltage directly to that internal contact of the transformer where the voltage divider output was connected to.

author: kfitch42
author_rank: Frequent Contributor
timestamp: March 25, 2013, 07:32:18 pm
content: Hmm, looking at the data sheet for the device I see:QuoteIn order to keep you low-voltage DC stuff isolated from your high voltage AC stuff, the easiest solution might be to actually control the physical pot with a servo.

author: ftransform
author_rank: Frequent Contributor
timestamp: March 26, 2013, 01:08:01 pm
content: You are not looking at that maxim constant current load are you?That 500k pot had me confused for a while until I realized that its only there to save on battery life!

author: plantgrower
author_rank: Contributor
timestamp: March 27, 2013, 07:39:15 pm
content: Quote from: ftransform on March 26, 2013, 01:08:01 pmWould you mind explaining that in a bit simpler terms for a noob.