When you’re working within programmable logic control (PLC), process control, temperature control, or any other type of I/O control, it’s best to have some help monitoring the various switch contacts.
This Multiple Switch Detection Interface (MSDI) offers this capability for up to 22 inputs, making it perfect for the above applications and other uses as well, like single-board computers or an ethernet switch.
This MSDI board features an NXP® IC chip MC33978AES, which facilitates the main feature of the board. Switch status (open or closed) is transferred to the MCU through a serial peripheral interface (SPI). An include 22-to-1 analog multiplexer also lets you read the voltages on the switch inputs, giving you insight into battery voltage and IC temperature.
The inputs can also survive a reverse battery without a blocking diode. It does include a blocking diode from the input to the power supply to avoid any back-feeding of voltage or current into the IC when the input is higher than the VBATP pin.
There are two modes of operation as well: Normal and Sleep. Normal mode allows you to program the device and have it supply contacts with pull-up or pull-down current as it monitors them. Sleep mode provides low current and periodically polls the switch.
source https://blog.tindie.com/2020/09/multiple-switch-detection-interface-board-monitors-up-to-22-switch-contacts/
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