I need some help understanding a strange voltage drop...
I'm buiding a Motion sensor that when motion is detected will trigger a reset signal (single rising edge) on an ESP8266.
I'm using a AM312 as motion sensor itself that is powered by a 3.3V source and outputs a 3.3V logic signal for a couple of seconds when motion is detected.
The motion detector on itself is working great. I tested it before I soldered it to my PCB and I got a correct 3.28V output as expected.
When however I connect it to my PCB... suddenly the output voltage is barely 0.65V... This is not sufficient to be used as logical input... I don't understand why a 3.3V output when soldered to a pcb suddenly gives 0.65V... (yes soldering point are properly done, no bad contacts).
I'm providing you with the below schematic in case it helps.
Can anyone help me clarify why I get 0.65V instead of the 3.3V ?
What is the purpose of the connection to pin 7 = IO13?
Does it is an in- or output?
Well, you've got a capacitor on the output and with power off the voltage across it will be 0V.
When Vout goes "high" it will attempt to charge C1. C1's negative terminal is at 0.6V (B-E voltage drop across the BC547) and with the cap discharged so is the negative terminal. Now what I would expect is that Vout will then charge C1 to about 2.7V, but maybe it can't source enough current to do that, so it stays at 0.6V.
My first question is what is your "... I connect it to my PCB" ?
I tested it when the motion sensor was loose (fully disconnected, not soldered).
Then I tested it as well when it was soldered on my pcb.
my aim was to get 3.3V at output as well to ensure I got sufficent voltage to overcome the B-E voltage necessary to switch the transistor.
Do you think that with a smaller cap, I would reach the 2.7 or 3.3V faster ?
It's to read the status of the motion sensor when the chip comes on...
I've removed part of my schematic for readability, but I have other signals on my RST.
One of them is a diode to IO16. IO16 is a clock that periodically triggers a reset.
By reading the Motion sensor state on IO13 (pin 7) I can differnetiate between a periodic wake or a wake by motion.
I'd remove the entire assembly around that transistor. If what you want is a short pulse to reset the ESP when the motion sensor is active, then you should use a one-shot circuit.
Would be my guess as well... IF I needed a positive pulse.
The ESP needs a single rising edge at the RST GPIO.
Hence it is pulled HIGH at all times and momentarily put LOW using the transistor when motion is detected.
This is why I use the transistor in combination with the capacitor.
(Cap allows me to trigger the rising edge before the motion sensor goes to low again)
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