First Project Help - Digital Potentiometer

Hey All,

I have read and researched a lot but can't quite get the answer 100 per cent. Long story short I'm modifying some PC Speakers so the Amplifier is seperate. I plan on controlling this with an Arduino, Digital Pot and LCD Display.

After identifying that there were Double Gang Potentiometers used (I saw Rotary Encoder mentioned and that threw me off my confidence) I went about researching replacing them with a Digital Pot and saw this Post: Controlling a Digital Potentiometer Using SPI

Now if I was to remove the existing Analog Pot and connect the Wiper from Dig Pot in its place would this work? I have a feeling I'm missing something related to the power requirements.

See image below...

Now if I was to remove the existing Analog Pot and connect the Wiper from Dig Pot in its place would this work?

Maybe but probably not. The problem is that the signals into a digital pot must not go outside the power supply voltages. This is a problem with the negative voltages in the audio signal taking things below the ground level. Some digital pots have a negative supply input which you will have to power. Otherwise you need to lift the ground with a pair of resistors and AC couple your signal in and out with capacitors.

As said above, you'll need to deal with the fact that audio signals go negative, so you'd need to raise the audio ground above 0 (to the middle of the range between gnd and supply, probably), or use a digipot that can go negative (these do exist, but you'll have to read the datasheets - 95% of digipots don't), or do something else to address that. I know I saw a 15v range digipot in a human-friendly package (I think DIP-8, or a dual in DIP-14) that would let you go below ground while I was browsing digikey.

There's the MCP41HVx1 series which lets you have 36v between the ends of the pot (as long as supply and ground are within that 36v range, it can be negative or positive), but that's a bit excessive, and the package it comes in is a bitch to solder (TSSOP-14).

Regardless, on wiring it:

Pots have 3 pins, two ends, plus a wiper. You must connect all three of those to the digipot (one of the ends will be audio ground, the other will be input for that channel, and the wiper is output.). Also, in your drawing, you're not supplying power to the digipot - you need to do that ;-)

Finally, be sure to do this before the amp ;-)

DrAzzy: As said above, you'll need to deal with the fact that audio signals go negative, so you'd need to raise the audio ground above 0 (to the middle of the range between gnd and supply, probably), or use a digipot that can go negative (these do exist, but you'll have to read the datasheets - 95% of digipots don't), or do something else to address that. I know I saw a 15v range digipot in a human-friendly package (I think DIP-8, or a dual in DIP-14) that would let you go below ground while I was browsing digikey.

There's the MCP41HVx1 series which lets you have 36v between the ends of the pot (as long as supply and ground are within that 36v range, it can be negative or positive), but that's a bit excessive, and the package it comes in is a bitch to solder (TSSOP-14).

Regardless, on wiring it:

Pots have 3 pins, two ends, plus a wiper. You must connect all three of those to the digipot (one of the ends will be audio ground, the other will be input for that channel, and the wiper is output.). Also, in your drawing, you're not supplying power to the digipot - you need to do that ;-)

Finally, be sure to do this before the amp ;-)

Ah thankyou, that made a bit more sense to me, guess i'm off to hunt down the right components. I realised that after I did the image, was early down here in Australia.

Haha it will definitely be before the amp, i'm retrofitting an existing Amp

As an alternative to a digi pot, you could use something specifically designed as a volume control. Have a look at the PGA2311 or 2310 from Texas Instruments or the CS3310 from Cirrus. Both options are very good quality if you’re looking for proper Hi-Fi sound.

You still need to find a negative supply rail though.

Ian.

Nice chip, this is just what the OP needs. 8)

Grumpy_Mike: Nice chip, this is just what the OP needs. 8)

I'm using the PGA2311 in my current Arduino project and they're very easy to control. You can get small DC-DC converters that generate the +/- 5v rails from a single 5v input. Even listening to a very high quality audio signal through headphones I can't hear any noise from the DC-DC or the PGA2311.

Ian.

In the past I have used the TDA7318, you get a bit of a graphics equalizer with that one thrown in.