Following the first mock test performed on 2/20/2023, I was tasked with resolving an issue related to the weak signal seen by the Pico ADC from the IR sensors.
We expected upwards of 1V to 2V at the ADC from the photodiodes, but were only getting values between 30mV and 40mV. Initially I had assumed that this was due to a current issue from the 3v3 pin of the Pico which could only supply up to 300mA.
Simulating the circuit in Multi-Sim, including the Thermistor Circuit which is also attached to the 3v3 pin, I was able to confirm that the maximum current draw using our circuit was only 124mA at most which primarily comes from the driving of the IR emitters which each require 20mA to 30mA each to create a strong signal.
After confirming this, I set up a mock circuit on the breadboard which made use of a single IR emitter and photodiode to ensure that functionality should work as intended. Initial findings indicated something similar to what we saw during the mock test wherein the signal at the output of the photodiode was quite weak, only reaching ~200mV maximum. Separating the emitter from the photodiode resulted in the signal at the photodiode hopping to over 2V. It was at this point I realized that the close proximity to the emitters were saturating the photodiodes resulting in a nearly unreadable signal. The solution was simple, a divider would need to be placed between the emitter and photodiode to ensure only signals bounced back by an object would be received by the photodiode.
Next, this solution was tested on the vent visors themselves and confirmed to resolve the issue. During this testing, it was found that the sensor at window 1 was experiencing issues as the emitter was not functioning despite receiving the necessary voltage required from the 3v3 pin of the Pico. Testing the signal across the IR emitter using an oscilloscope, I was able to confirm that the emitter was wired in reverse, the voltage across the emitter was a negative voltage thus impairing function and will need resoldered.
Lastly, to further confirm, a secondary emitter was wired to a 3 Volt supply to ensure the photodiode of the window 1 sensor was functioning. The code used for the IR sensors takes a difference between the signal at the ADC when using only ambient light (which typically spikes to 1.2V to 2V) and compares that to the signal when using IR light. Typically this results in a difference of 1V to 1.8V indicating that the window is up. Due to the emitter being wired in reverse, the signal sent to the circuit results in a negligible difference meaning that, despite the photodiode working, until the emitter is replaced the sensor will not accurately determine if the window is up or down.
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