How to multiplex open drain sensors

Question

I have 64 digital hall effect sensors with open drain outputs (A3144), and would like to read their outputs with an MCU. Is there a simple way to multiplex these sensors to limit the number of IOs needed? Reading bandwidth is low.

My thought is as follows:

Arrange the sensors in a 8x8 matrix, shorting the outputs of every row, and the grounds of every column. Interrupt the power supply on the GND side with a mosfet, and cycle one column at a time like conventional multiplexing. The unsupplied sensors will see their GND go up to VCC and won't be able to pull down the line even if their output is active.

I have some concerns:

• in case the active sensor in the row is low, the other sensors will see -5V on their outputs wrt their GND. Do I need a diode in series with each individual output for protection?
• is it a bad idea to repeatedly power cycle the sensors at moderate frequency? (no startup time is specified in the datasheet

Answer 1

Usually switching the ground of a system with data connections is a poor idea, and this is likely not an exception to that.

The datasheet says that absolute maximum rating is that output pin has -0.5V compared to ground pin.

So if like you say, ground pin floats at VCC when disconnected, another output may pull the common data wire low. If this were a regular IC, it would power up as pulling the data wire low also pulls GND low via internal protection diodes.

But what you could do is multiplex the supply voltage. Or the data.