#1669

Episode 1669 chip of the day
serial interface programmable potentiometer
copied from: www.hackster.io/umpheki/ardui...
Board from ideaspark. search for 'Nano V3 Board ATmega328P CH340 Controller with 0.91'' OLED Display for Arduino'
Be a Patron: / imsaiguy

[@MickHealey]

Nice video, thanks. At 2:18 you mentioned that you were not sure how they accomplish the potentiometer functionality inside a chip. Having used these before, I can tell you that there are 256 resistors in series (for the 8 bit version) strung between the pot ends P0A and P0B. This gives you 257 possible voltage levels (both ends + 255 junctions along the string). As you suspected, FETs are used to tap off the appropriate resistor in the string to give the wiper voltage at P0W. These are great little chips. I used the dual version to design some test equipment for the radiotherapy company I worked for, using Arduino as the controller. This won me my one and only patent. So, I love this chip 🙂

[@IMSAIGuy]

I would guess it is not 256 resististors but something like an R-2R ladder of 8 bits so only 8 FETs needed, but looking at datasheets it does look like 256! have you ever seen a die photo? nevermind: www.experimental-engineering.co.uk/2017/02/02/ic-decap-analog-devices-ad8403-digital-potentiometer/

[@MickHealey]

@@IMSAIGuy I just accepted that the datasheet was correct regarding the chain of 256 resistors. I never considered looking for a die photo, as I had bigger fish to fry at the time. With hindsight, it is an interesting question though. Unfortunately, the link you provided doesn't work for me.

[@rhp9797]

We do really love Chip Of The Day! Amazing video series you have going!

[@matteo234321]

I use a similar digipot to do the auto-ranging feature for the input of an ADC on a bed-of-nails test fixture at work. Linearity isn't the greatest, especially with temperature changes, but still a nice IC!

[@stefflus08]

I've smoked some digital pot in my days

[@hrvstmusic]

😂😂😂 smoking hash with a soldering iron 👌🏻

[@W1RMD]

I'm an analog home grown kind of guy.

[@hrvstmusic]

@@W1RMD😂🙏🏻

[@brianbrumfield3330]

The biggest problem with the digital pots is the limited voltage on the resistor pins.

[@W1RMD]

Thanks for showing. Have a great day and weekend.

[@fer_fdi]

Very cool. And what a beautiful HP meter!!! : )

[@IMSAIGuy]

HP427 kzbin.info/www/bejne/jIaan5-QZ6l0gcksi=FH0pXa7pOEIvt32j

[@frankowalker4662]

Neat little chip, with so many uses.

[@RonDogInTheHouse]

Been using the digi-pots for some time now. What I didn't know was the Nano with OLED, need to get me some of them, they'll make prototyping easier. Thanks

[@danielmantione]

It is a nice chip, but you may want take a look at the SLG47004. For a lower price than the MCP4131 you get two digital rheostats that can be serially programmed, and there are a hell of a lot more interresting function blocks on that chip. The price that Microchip asks seems fair for the functionality, but, compared to the SLG47004, it suddenly is way to costly.

[@christopherjackson2157]

Oh neat ive never seen a digital pot. That could certainly come in useful

[@MAV3NX]

Love these guys.....except for the 2.5mA current limit😢

[@aduedc]

I guess with dual pot of this chip, one can use Wien Bridge Oscillator topology and make Digital Controlled Oscillator (DCO) at low frequencies. As you know making low phase noise VCO at low frequencies is difficult.

[@Enigma758]

I think the digi-pots have limited application compared to "physical" pots since they typically can only handle a few mA.

[@hayleyxyz]

Really cool chip. I'd be interested in how they implemented this in silicon. Since it's only 8 bit, maybe a huge voltage divider and the logic just chooses which route to take? Thanks for sharing

[@barrybogart5436]

That's pretty cool. I'm still trying to get my old head around passive components imbedded (simulated?) in IC packages. Can they do dual gang nonlinear variable caps and ferrite slug variable inductors?

[@simontay4851]

Is this Arduino board with the OLED display compatible with LCD smartie? LCD Smartie is open-source software for Microsoft Windows which allows a character LCD to be used as an auxiliary display device for a PC.

[@pauldery7875]

Can this be used as an electronic volume control?

[@IMSAIGuy]

yes

[@simontay4851]

What is the power rating of the digital pot IC?

[@Enigma758]

They tend to me rather low, I believe only a few mA.

[@lahtinenk]

I have wondered if this is suitable for audio volume control or mixers?

[@IMSAIGuy]

yes

[@RK-kn1ud]

I'm surprised you could even locate a Mini USB cable in 2023 to use it.

[@user-cf7be9km5m]

Do I understand correctly that one chip costs about $5?

[@IMSAIGuy]

no, less than a dollar

[@minhajsixbyte]

digital potentiometer vs DAC?

[@__--JY-Moe--__]

a chip right off the O'le EE block! that's just what I'm looking @!! he..he..🤓but mine doesn't have a data, it's just a blind chip!

[@bayareapianist]

If there is a DAC in your arduino chip, why would you want to do this?

[@IMSAIGuy]

you are correct, but this was just a simple demo of the part working. it can be used in many other applications where a DAC could not be used just as controlling the gain of an opamp circuit.

[@bayareapianist]

@@IMSAIGuy Do you mean the pot is isolated from voltage rails?

[@IMSAIGuy]

@@bayareapianist yes

[@devilvortex1]

0ne step how many ohms?

[@IMSAIGuy]

they come in different values. this one is a 10K pot, so each step is 10K/256

[@devilvortex1]

@@IMSAIGuy I"m not good reading datasheets but If I understood one wiper step equals 75 ohm. I have 10k pot 75x128 = 9600 right?

[@sefarkas0]

What bonehead made a module with a display where the USB connector is taller than the glass?

[@georgesampson4714]

Maybe the bonehead who figured out that a recessed display is easier to read under varying ambient light conditions than one mounted flush or proud of a panel.