How to detect multiple digital sensor with one micro controller input?

Question

I would like to connect multiple TSSP4038 sensors together in such a way that I only have one output (let's call it Y_out), if any of the sensors output is HIGH then Y_out is also HIGH (regardless if some of the other TSSP4038 sensors are low).

According to the datasheet, the TSSP4038 output pin supplies a current of 5mA and a voltage of -0.3 to 5.5 (depending on Vs).

I am thinking the best way to do this is to connect a diode to the output of each sensor (so they don't drain into one another), then connect the nodes after the diodes together to a Pull-Down resistor. If any of the outputs is HIGH then then a voltage across the resistor will be detected.

Would this work? Any suggestions on a better way to do this?

Answer 1

I have used these before and your specs may not be what you want. Received carrier is logic "0' and no carrier is Logic "1" which has an absolute max output voltage of 0 to 5V +/- 1 Schottky diode drop of 0.3V for ESD protection.

Since the output is NPN collector out with 33kohm pullup to Vs(+) in the "off" state, you want sensors with a weaker or no signal to be ignored , a logic AND function for any low input to give a low output (or NAND ) and but never a logical OR as a sensor with no signal will remain high.

The AND function is all wired in parallel which is bad practise for debug, so take note. I would suggest a CMOS 4068 - 8 Input NAND gate.

But since the max current for a "0" is 5mA if using 5V then each external pullup draws 5V/33k=0.15mA you can use up to 33 in parallel.

Input data patterns shown in spec Fig 1 must be adhered to match the AGC and BW filters for optimal reception for \$t_d,t_{pi}, t_{po} \text{ and } f_o\$

Answer 2

if any of the sensors output is HIGH then Y_out is also HIGH (regardless if some of the other TSSP4038 sensors are low)

There's an open collector circuit, but note it is Active-low wired-OR / active-high wired-AND circuit, thus if any of the sensors will detect the event, you will have low, not high.

According to the datasheet, the TSSP4038 output pin supplies a current of 5mA and a voltage of -0.3 to 5.5 (depending on Vs).

To my understanding you are going to use this pin as input, not output. During power on and initialization GPIO pins are usually tri-stated until you configure them in specific direction.

I am thinking the best way to do this is to connect a diode

I have tried similar circuit in the past myself; results were not satisfactory (do not remember why - probably there were false positives). Check if your sensor output is already open collector, and use logic IC with open connector output if it is not. The only overhead here is that this IC will need power supplied.