How to connect a digital sensor to the input and output shift registers at the same time?

Question

Electronics

Greetings! I need to connect a lot of these proximity sensors to stm32. The general meaning of the circuit: by installing a capacitor, an analog sensor as a one-bit ADC turns into a digital one. To read the value, first, 250-800 µs, depending on the required sensitivity, we hold a logical unit on the signal output, charging the capacitor, then we transfer the output to the input and read. I need to connect 20 such sensors, it’s a pity for the legs, and the current per leg and port is very tight. Therefore, I want to connect sensors to shift registers, charge a capacitor through a transistor through a register with a parallel output, and read a value through a register with a parallel input. How to do this correctly so that charging the capacitor does not burn the input on the register or set log.1 on it?

Answer 1

Analog multiplexer. Like 74HC4051. We connect (signals S0-S1-S1) to the desired sensor and charge-discharge-measure. You can expand them as needed. You can apply to the address (signals S0-S1-S1) through a shift register, if there are a lot of switches and you feel sorry for your legs.

Answer 2

You can supply an output register with a Z-state 74HC595 and an input 74HC597. Limit output currents with series resistors. But accuracy and stability are questionable.

Answer 3

There is an alternative hardware-software platform implementation for all such and other situations that arise during the development process.
60 output / 1600 input ports (ADC, 12 bit, 0 - 3.300V)