Digital volume control

[letsrelaythat]

Hi All,

Have been doing some reading on a few websites, basically I'm trying to make an audio switcher, with volume control, all controlled by a PIC.

I am considering using something like transistors, however audio is AC so this won't work. The switching I was going to do with relays, is this the best option?

Just wondering what my options are, in terms of controlling the level of the selected audio signal. I have looked into the Dallas DS1666, but it will be hard to get hold of in a short time.

Any other ideas, or recommendations regarding this.

Thanks guys,

Tim.

 

[Nigel Goodwin]

There are various specific chips to do the job, both volume control and source switching - however, they aren't very common, and you would probably have to obtain one as a spare part?.

The switching can also be done using CMOS switches, or even diode gates, both have been used in commercial amplifiers.

 

[justDIY]

CMOS switches for the routing (74HC405x), digital potentiometers for attenuation (volume)

National has a few pots to choose from specifially designed for audio:
visit --> **broken link removed** and click on "Controls"

 

[letsrelaythat]

Hmm well the switching isn't my main concern at the moment, I just want to work out how to control the level from the PIC.

I'll look into this DS1666 tomorrow, from what I'm reading it sounds like the easiest thing. I'll also pick up a few circuits at work tomorrow on those 74HC chips to see if I can work anything out.

Does anyone know if (with the DS1666) I can set a specific value, or is it just up/down commands that I can use.

Thanks all,

Tim.

 

[justDIY]

well, the 1666 is specificly "up down", probably designed for low-cost applications.

check out the MAX54xx family, with a 3 wire SPI interface, or the DS1802 has a simple 3 wire serial interface... thats kind of neat, you can control the volume through programming via the serial interface or by manual pushbutton

 

[Oznog]

Microchip's MCP42xxx series of digital potentiometers (10k,50k, 100k). SPI interface.

As you concluded a transistor is not a good switch. In a crude sense you could have a node which is DC biased above ground and a transistor shorts it out to ground, but this is unnecessarily crappy.

There's a line of very common, cheap, quality analog switches (more commonly called an "analog mux", "analog multiplexer". 4051, 4052, 4053 I believe, each has a different switch configuration. I don't list the entire part number because each mfg adds their own:
SN74LV4051
CD4051
74HC4051

There are high and low voltage versions of each of these chips. The downside of the higher voltage one is it has a greater on-state impedance IIRC.