Opto 16 channel

OPTO-IO-BOARD

This board provides 16 independent voltage detection channels. The channels can be configured to detect Open/Ground signals or Open/5-40V signals. Each channel has a LED that indicates if the channel is ON or OFF, a currently limiting Resistor and an Opto-Isolator. Each channel is then inputted into the MCP23017 IC that is setup as an Open/Ground detect. The MCP23017 has an internal 100K internal pullup to 3.3V that is grounded by the Opto-Isolator when the Input is Active. The MCP23017 samples it's inputs and reports their state over the I2C bus. The Adafruit HUZZAH32 - ESP32 Feather board is used to poll the MCP23017 and send the current state of the channels over the network. The HUZZAH32 Feather can be used over Wifi or with the optional Ethernet FeatherWing.

The board was designed to provide a large input voltage range. The input circuit is a series of two diodes and any input that provides enough current to activate the diodes will trigger the input. The input trigger point is approximately 33ua because the Opto-isolator only has to sink the 33ua provided by the MCP23017 100K pullup to 3.3V. A input 0.5V over the two diodes forward voltage is enough to do this. The minimum input of 5V is more than enough to trigger this as the LED ( approx 2.2V ) and opto-isolator ( approx 1.2V ) have a combined forward voltage of approximately 3.4V and the Opto-isolator has a gain of approximately 70% at this low current level so ( (5V - 3.4V) / 10K ) * 70% => 112ua which is more than the 33ua sourced by the pullup resistor. Note: Some LEDs can have a forward voltage as high as 3.3V which would result in a current of 35ua just a little bit more than the 33ua required.

If you would like to change the voltage level trigger you can add a Zener diode in series to the input circuit. The Zener diode will increase the input level trigger by it's value + approximately 5V. So, if you want to trigger at say 20V you can put a 15V Zener diode in series on the input.

The input voltage is limited by 10K resistor at 1/2W and the max steady state current rating of the input diodes ( Typically 20ma ). At 40V input there is only approximately 3.66ma of current at 0.133W going through the input circuit this is far below the LED's 20ma max at around 4W. The input was rated at 40V ( approximately 27% load ) as a very conservative limit not knowing what conditions the circuit would be used in. The real 50% max input threshold is approximately 53.4V at around 1/4W and 5ma. The 100% load is approximately 74V at around 1/2W and 7ma.

Folder structure

• doc : Contains PDFs of the board design and the BOM.
• hw : Contains the Gerber and Kiacad design files for the PCB.
• sw/opto : Contains example source code for using the board with the optional Ethernet FeatherWing.
• sw/opto_wifi : Contains example source code for using the board with wifi.
• sw/sample_receiver : Contains example source code to receive and print the channel status on change.

You can find an overview of the Adafruit HUZZAH32 - ESP32 board at the link below.

• https://learn.adafruit.com/adafruit-huzzah32-esp32-feather/overview

You can find an overview of the Adafruit Ethernet FeatherWing at the link below.

• https://learn.adafruit.com/adafruit-wiz5500-wiznet-ethernet-featherwing/overview

You can find the MCP23017 data sheet at the link below.

• https://cdn-shop.adafruit.com/datasheets/mcp23017.pdf

To build the code you need to download the following SW :

• HUZZAH32: https://learn.adafruit.com/adafruit-huzzah32-esp32-feather/using-with-arduino-ide
• Ethernet FeatherWing: https://learn.adafruit.com/adafruit-wiz5500-wiznet-ethernet-featherwing/usage
• MCP23017: https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library

To edit the PCB design you can download Kicad at the link below.

• https://www.kicad.org/

License

The contents of the doc and hw folders are licensed under the Creative Commons Attribution 3.0 license. The contents of the sw folder is licensed under the MIT license.