I have some old vellman kits for generating steam engine sounds. They use 100k pots to change the sound speed.
Is it possible to obtain 100k digital pots to use here. I can use the arduino, as in the description of the DS3502 pots, and drive the throttle channel from the rc receiver into the arduino. That side I have done with some success in motor mixing in boats.
Is there a better way to do this?
The 100kohm pot, as a manually variable resistor, is on the negative input of a LM324 op amp.
Best regards CC
Sounds viable to me 
An alternative might be a DAC + Op-Amp, but whether that’d be any better or not depends on the rest of your setup
I tossed the scenario to chatgpt and it concurred but also had some good additional advice (and a funny one!), compare its suggestions with your needs and voila!
Hi
Thanks for the response. I attach the schematic of the sound generator. The pot in question is RV1. (Operating as a variable resistor) My problem might seem to be that the circuit runs at 9v, and I am not sure if many 100k digital variable resistors are suitable for the resistance side at that voltage? TheDs3502 is, but only 10k!
Yes the suggested option of a servo driven pot has been considered, but its not too “techy”!!
Can I repeat this to the chatgpt, or would I have to setup an account? Most of the suggested are only 5V limited?
Many thanks ChrisC
Hi
I have tried the digipot, dfr0520/rb.dfr.790, in the circuit, and it doesn’t seem to mind that the potentiometer part of the circuit runs from a 9v supply. It has run, ramping up and down for over 5 mins, without any temperature rise, or misbehaving!
I know it’s not supposed to work, and may not do so for very long, but with few other options, I thought I’d give it a go!!
Best regards
Chris C
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Excellent work!
I think the 5 volt requirement is for the logic side of the digital potentiometer. The actual potentiometer usually can handle more voltage but you do need to check the datasheet to find out exactly how much.
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Yeah, many thanks, I was sort of hoping that the resistance side was a bit more “adventurous”, though the data sheet also says 5v max. We shall see if exceeding that by a bit is guaranteed to release the smoke, or there is some leaway!!
As I mentioned it has run for some minutes, and as its only a hobby model boat application it’s not too critical.
CC
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It looks as though we are still lucky. The digipot is working fine, in fact both channels are operating, and singalling into a pair of the 9v vellman kits steam sound generators. The longest run is 20mins on the bench, and due to be embedded into a model steam tug in the next few days. (Tug is setup with electric motors, sadly!)
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While I am on a roll… I am wondering what is the best way to replace the SW1 push button in the sound generator circuit, to allow remote operation?
I know the most straight forward is using a relay, but this seems heavy handed?
I was wondering if a transistor or opto isolator could be used, but wasn’t sure how they would integrate round the push button?
Supply, grounding and milliamp limitations seem to be needing taking into account?
What is the best route?
CC
