OT: Question for electronics guru: Replace pressure sensor with light sensor?

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DogChainX

[H]ard|Gawd
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Offtopic, sort of.

So, I have this little project:

My wife and I have a newborn little baby boy. We bought a baby monitor setup, however, it REQUIRES the pressure plate, which the baby sleeps on, to be plugged in. I don't want this plate having to be plugged in all the time. The pressure plate plugs into the main monitoring unit via a 3.5mm TRS connector (think headphone/speaker/audio jack).

I have a spare 3.5mm audio cable, and cut it in half. I was hoping just having the wires unshielded at the end and have them near the radio antennae it would generate a signal close to what the pressure plate/sensor can generate. I'm wrong (i have no idea what i'm doing, just shooting in the dark).

So, I was thinking maybe I can hook up the end of the spliced audio cable to a light sensor?

Anyone have any suggestions on how to solve this problem?
 
The question is what kind of device the pressure plate is.

If it's just a switch, requiring being plugged in would mean it closes when weight is on the switch.
If it's a resistor with the resistance varying based on weight, it has to decrease resistance with increasing weight over the sensor.
If it's a capacitor... hell if I know. That's expensive to implement and is unlikely.

It's probably just a switch. Some suit who doesn't want to miss out on a Cuban cigar worth of profit would never take a variable resistor where a switch is "good enough".
 
MisterDNA said:
The question is what kind of device the pressure plate is.

If it's just a switch, requiring being plugged in would mean it closes when weight is on the switch.
If it's a resistor with the resistance varying based on weight, it has to decrease resistance with increasing weight over the sensor.
If it's a capacitor... hell if I know. That's expensive to implement and is unlikely.

It's probably just a switch. Some suit who doesn't want to miss out on a Cuban cigar worth of profit would never take a variable resistor where a switch is "good enough".
Click to expand...

For some odd reason, I KNEW you were the one that was going to respond to this. I should have just PM'd you the question. :D

I did hook up the red/green/bare wires within the audio cable to hope that a return voltage might work. Nope, so the switch idea isn't working. I'll have to break out the voltage meter to see if there's any power acting as a circuit.

From what I've read, pressure sensors actually produce their own signal and act as a transducer. So i'm not sure how I can replicate this unless I can pinpoint that signal, which is beyond any electronic tools I have available, nor the background in electronics to figure it all out.
 
It might be a capacitive pressure sensor--even cheaper than a switch. If it is, the monitor senses the change in capacitance when you put the baby on. in which case you'll need either a large assortment of capacitors to test in its place, or an LCR meter to figure out what the capacitance is.
 
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