Hi wonderful community,
I am having problems when reading the signals coming from my PIR sensors on a PCF8574 WaveShare card.
I was about to get crazy when reading always 1 in all the pins after restarting and don't know why sometimes I read 0s.
Anyway, the pins are set as INPUT because my idea is to read the state of the PIRs connected to it.
When the PIRs detect movement they send a 3,3V signal through the output pin which I connect directly to the corresponding pin on the PCF8574 board.
Everything is well addressed (the I/O expander) because I can read the status when connect directly the PINs from the PCF8574 to VCC in the protoboard, that's why I guess the problem is not there.
My problem is that I don't understand why when the PCF8574 receives the same +3,3V signal from the sensors, it does not read them as HIGH. I have checked the current flowing in both cases (when connecting the I/O pins to VCC directly, which is about 60-70mA), and (when connecting the +3,3V from the output of the sensor to the I/O pins on the PCF8574, which is very low 2,5mA).
So, I don't know if it is due to the Sensor is not available to deliver more current and so the PCF8574 is not able to detect that as a HIGH state, or simply I am doing something wrong.
I have been thinking to then put in the middle some Reles which leads the I/O expander Pins to VCC when the corresponding PIR sensors activate them, but that would be against what I am precisely looking for (reduce the total consumption). I have understood that a Rele average consumption is around 90mA, which is totally out of the range I am expecting to.
Finally, why is this happening? Is it not supposed to be very simple? just connect the expander and then start reading the signals normally? I don't think this PCF8574 is that useful when using it as an INPUT PIN expander. am I doing something wrong? Shall I add pull-up or pull-down resistors to the I/O Pins?.
Well, let's see how we can start, I will not bother you guys with more details yet. If you want to see the code or some pics, just let me know.