Adafruit ADG728 1-to-8 Analog Matrix Switch

The Adafruit ADG728 1-to-8 Analog Matrix Switch is an ideal alternative to relays for those seeking a smaller and lower-power technology that will not wear out mechanically. It can easily connect up to eight analog signals, functioning similarly to a set of eight mechanical switches. This conveniently-designed breakout allows for use of the ADG728 switch with signals up to 5V, eliminating any need for intricate soldering.

The ADG728 employs the I2C protocol to designate the active channel among the 8 available, enabling a connection to the single analog 'D' pin. Unlike digital switches and multiplexers, these switches have a bidirectional signal flow and can act as inputs or outputs interchangeably. This allows for the D signal to function as an input for 8 outputs or the 8 inputs to function as one output.

The ADG728 serves as a matrix switch with 8 independent switches instead of a selecting multiplexer. This allows for signal routing selection as well as the ability to combine signals by turning on multiple switches. In essence, it acts as an SP8T switch.

Unlike a relay or mechanical switch, analog switches don't wear out, and the switch time is near instant, about 100nS. The ADG728 chip also guarantees break-before-make so the deselected switches will open before selected switches close.

However, there's a few things to watch out for:

• The Vin power pin (the red wire if using a STEMMA QT cable) must as high as the highest analog voltages you want to switch. That means if the analog signals are no more than 5VDC, the V+ pin must be higher than 5V. You cannot power this pin with 3.3V and switch 5V signals.
• It cannot switch signals below ground. No negative voltages can be applied to the Switch or D pins!
• Analog switches are for signals, not power! Since this is not a mechanical switch, the signals pass through circuitry that is not designed to source or sink current. This is great for analog signal voltages, and is not good for providing more than a few mA of current.

In addition to the 8 switch S pins and the D pin that can be switched to, there's also two I2C address pins so you can change the default address from 0x4C up to 0x4F. There's also a reset pin if you want to immediately set all the switches to open.

To get you going fast, we spun up a custom-made PCB in the STEMMA QT form factor, making it easy to interface with. The STEMMA QT connectors on either side are compatible with the SparkFun Qwiic I2C connectors. This allows you to make solderless connections between your development board and the ADG or to chain it with a wide range of other sensors and accessories using a compatible cable.