Adafruit ADG729 Dual 1-to-4 Analog Matrix Switch

The Adafruit ADG729 Dual 1-to-4 Analog Matrix Switches provide an efficient and reliable alternative to mechanical relays, with a smaller and lower-power technology. This breakout allows for easy use of the tiny surface mount chips, enabling connection between two sets of four analog signals up to 5V without the need for complicated soldering.

The ADG729 utilizes I2C communication to enable/disable the 8 channels switches. Four channels are linked to the DA analog pin while the remaining four are linked to the DB analog pin. Unlike digital switches and multiplexers, these channels do not have designated 'input' and 'output' signals, as the signal direction is bidirectional. This allows for various signal routing options, such as using the DA or DB signal as input for 4 outputs, or the 4 inputs for a single output.

The ADG729 is not just a multiplexer, but a matrix switch with 8 separate switches. This allows for signal routing and combining multiple signals. For all 8 signals to be routed to one pin, consider the ADG728.

Unlike a relay or mechanical switch, analog switches don't wear out, and the switch time is near instant, about 100nS. The ADG729 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 DA/DB 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 two D pins that can be switched to, there's also two I2C address pins so you can change the default address from 0x44 up to 0x47.

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.