I guess I can ask here first.

I've a small PCB from a printer apparently. It has a sensor on it, but Idk what its supposed to sense. Would that be an appropriate question on the main EE site? I've created a schematic and found info on the only IC on it, but I can't figure out what the sensor itself is supposed to do

@machineman311 Post the picture of the PCB in this chat first. There's a good chance that we can answer your question in the chat.

I dont have the reputation to be able to post pics here

@machineman311 Could you upload it somewhere (flickr or such) and post a link?

Yes. Dropbox.

dropbox.com/sh/0n1ixtkjtwkv4wo/AACXXQiQ7VU8T8q0GBt64W5ma?dl=0

The sensor and connector are the only things on their side of the board, and the sensor has a vented cover with a little strip of Styrofoam lining it.

I've no clue what values should be pumped through this thing, but I think 1 is Vcc, 2 data, 3 Gnd, and 4 data. Maybe?

I found the board online but its only referenced as hex inverter, or simply "sensor." But not what it should be sensing :/

Looks to me like it could be a capacitive moisture sensor. The 7404 is a hex inverter; likely two or three are used to form a primitive oscillator, with the capacitor defined by the moisture detected. But why a regular inverter and not a Schmitt-trigger inverter? Maybe you have some ideas @NickAlexeev

pictures uploaded to chat on behalf of @machineman311

Thank you @NickAlexeev.

I labeled my pins wrong.

I think its 1 data, 2 Gnd, 3 data, 4 Vcc

The diode and transistor are my best guesses based on Google

If you measure 0 Ohms between J1 and J2, then the far-right capacitor (smallest component) is actually a ferrite bead inductor.

I think the pins are 1 = chassis ground, 2 = Vss, 3 = pulse freq out, 4 = Vdd (5v). I'd apply 5v, through a 1k resistor, between 4-2, and use a multimeter or oscilloscope to see what comes out of 3-2.

The output frequency should be dependent on heat or humidity.

I read around 8Kohms between J1 and J2. And it slowly decreases, about 10ohms/sec (average guesstimate)

I'll set up the test this evening. Just to be sure, +5v on J4 and 0v on J2. One scope channel between J2(0v) and J3(signal)?