This is a 16 channel low side switch for on/off control of DC loads (including inductive with external protection eg diode across coil).

Each channel includes a higher current FET switch rated for a few amps per channel, and a lower current NPN switch for smaller loads or other feedback/indicator purposes.

There are also 16 inputs which can be used to control the outputs or trigger other functionality based on programming.

The 16 inputs and 16 outputs are controlled by two on board MCP23017 GPIO expanders over an I2C bus. Using the I2C bus, the 16 inputs are read, processed, and outputs can be controlled as needed.

The I2C bus can be controlled with an on board ATTiny device, or by removing jumpers, it can be controlled by an external I2C bus controller connected via headers/screw terminals.

When using the on board ATTiny as the I2C bus controller, the ATTiny's UART can use the on board RS485 transceiver. This can be used to process incoming data or provide feedback over RS485, allowing control over how the inputs and outputs are used.

This project is intended for use in a hobby electronics project environment, eg. a controlled research and development work shop to assist in the design and test of various other projects, ideas, and concepts.

It is not intended to be used as a stand alone or complete/refined product.

This design may be refined on an ongoing basis as needed, including design corrections or changes to fit or function.

If used in a situation where safety or other regulatory approval is required, it is the responsibility of the user of this design to ensure all applicable laws and regulations are followed.