[SeanHodgins] has a project in mind where he needs to sample over 500 analog sensors. To get ready, he made a breakout board for 32-channel analog multiplexer device he wants to use. He put the project out on Hackaday.io and also has a video tutorial you can see below.
There are five input pins to the chip which lets you connect one analog pin to any one of 32 analog pins. Of course, in addition to the five control lines, you need some handshaking lines, too so you could use as many as eight digital pins to control the device.
The device in question is an ADG732. The board layout and the source code is all available on GitHub. Because the switches are analog, they are bidirectional. That is, it isn’t really connecting one output to 32 inputs. It is more like a 32-position switch that connects a single pin out of 32 to one other pin.
Keep in mind that these sort of devices have some practical limitations. For example, the switch resistance is nominally 4 ohms at room temperature. The switches that route the signals also have some capacitance that varies depending on if they are on or off. There’s nothing wrong with any of this, of course. But it isn’t quite the same as having, for example, a 32-position rotary switch. Of course, it can switch faster than a mechanical switch and is easy to control, so — as always — its a tradeoff.
Notice, too, that the mux chip can operate rail-to-rail. However, for some applications, you’ll need a negative supply and the device can accept a +/- 2.5V supply for that purpose.
There are a lot of uses for something like this. Routing audio signals, for example, or switching between multiple test points in an automatic test system. We looked at a mux last year with a paltry eight channels. Then again, you can always go old school and make mechanical multiplexers.