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Digi-pot sugestions, please

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Bern1937

New Member
I am quite confused as to which digital potentiometer would work best, with the simplest circuitry.
Wants: – 5 volt OK, but 12 v better – 8 pin DIP package – A command input to set wiper at one end at any time – An input to advance wiper one increment per pulse, always in same direction. – I think all the other standard pins and actions, I can work with. – Resolution is open at this point. – Anybody familiar enough with these devices to point me in some direction. Tnx
 

dknguyen

Well-Known Member
Most Helpful Member
I am quite confused as to which digital potentiometer would work best, with the simplest circuitry.
Wants: – 5 volt OK, but 12 v better – 8 pin DIP package – A command input to set wiper at one end at any time – An input to advance wiper one increment per pulse, always in same direction. – I think all the other standard pins and actions, I can work with. – Resolution is open at this point. – Anybody familiar enough with these devices to point me in some direction. Tnx
What device works best will depend on what you are using it for. I personally always found them to be more trouble than they were worth and always tried working around needing one. You never even mentioned whether you wanted a bit interface or serial.

I don't think I've seen a bit interface one that has a command that brings the wiper all the way to the end- always just incremental up/down. Even if they exist, the 8-pin devices don't have enough pins to support that funcitonality..

Vdd
Vss
End1
Wiper
End 2
Up/Down
Increment

That's 7 mandatory pins right there and it would take another two pins to be able to jump to either end (End1/End2 and Jump) which pushes you past 8 pins.

This wouldn't be an issue with SPI, and SPI can just barely squeeze in on 8-pins if you the pot sacrifices the MISO line so that it can only ever receive data, and never send any data back to the master.

I guess what I'm getting at, is that at 8-pins they're all pretty much the same wiring complexity since there are no extra pins to work with so all bit-wise devices will have identical pin funcions and all SPI devices will have identical pin functions. There's no wiggle room to do things differently.

The wiring for SPI could be considered simpler but you pay for it in code complexity. (I'm also pretty sure the SPI pots do not possess an increment/decrement command even though they could support one. You just write what absolute resistance you want and keep track of where you are in the microcontroller if you want to simulate increment/decrement behaviour).
 
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atferrari

Well-Known Member
What device works best will depend on what you are using it for. I personally always found them to be more trouble than they were worth and always tried working around needing one.
One relevant point is the pot retaining or not the setting at the turn OFF time. That makes for a different functionality when turning ON next time.

Xicor used to have some interesting ones, but that was long time ago.
 

Bern1937

New Member
Flyback, Your suggestion is possibly a choice. On power up it goes to center. If I pulse power off and back on I will know where it is, and possibly can go from there. What I would rather have is a reset pulse that puts the wiper at one end on command.
 

schmitt trigger

Well-Known Member
Its been a long time since I last checked, but many digipots include non-volatile memory such that its cursor position remains after power down.
I would suggest that you consider one.

There are also I2C controlled devices. They allow the wiper to quickly jump from one position to another, instead of stepping thru each intermediate position as an increment/decrement interface does.

Additionally, if your board also includes other I2C devices, you only require two pins from the microcontroller, allowing for smaller devices to be used.
 
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