I am working in a project where my sensor nodes are powered by a 18650 shield holding four batteries. I think of hocking up two solar panel to each node, for two reasons : 1- charge the shields and 2- A wake up signal to the arduino when the output of one of the panels drops below the other
the design :
This is my first project and I am clueless, so any suggestions will be very much appreciated . so far the node sensor contains a radio module and a sensor.
what should Nano do?
Are you aware the processor has its own comparator you can set up and use?
I'm not sure the comparator will work with solar panels. I think of solar panels as current generating devices. So long as there is enough sun on the darker panel that its open-circuit voltage is at least as high as the voltage the brighter panel is currently operating at, then the two panels will have the same output voltage, but one will be producing far more current than the other. If that's correct, then comparing voltages won't really work. In fact, variations in the output diodes might result in the panel in shade having a higher voltage than the one in sun.
Edit: However, the fact that the forward voltage drop across the diodes increases with current may allow the circuit to work.
Can you explain what the Arduino will do differently depending on which panel is in shade?
I don't know about the OP, but I certainly didn't remember that at all. I guess that's because the Arduino designers didn't include anything about the comparator in the IDE lingo. Anyway, thanks for posting that.
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Send a radio signal to update it's status
radio module not shown
I am interested in 1) A way to compare the output of the two solar panels when one of them is shaded, and send a wake up signal to the nano when the output dips under a a certain threshold, apparently current is effected more by the change in light, so i am trying to find a way to measure the two currents. 2) How to charge the battery and power the nano at the same time. i am trying to optimized the nano to activate and update its status by sending a message to the master node. the mechanism would be as follows : one solar panel output drops below the threshold -> using the comparator circuit to send a wake up signal with the pin change, the sensor will work for a while and radio will update its status by sending a message to the master until it gets an acknowledgment.
if it matters i am using a sx1278 radio :
Can i used it to compare the two currents coming from the solar panels ? and any other middling components should there be to regulate the connection ?
What you said is factual, current seem to change much more drastically than voltage in shade. what i am trying to do is utilize the solar panels as 1. Powering source for the circuit to charge the batteries, which in turn power the nano. 2. as a sort of car detection method, a plan A if you may, where when a car enters a parking slot, where the sensor node would be placed (under the parked car), the solar panels are placed such that the car entering would cover one of the solar panels before the other, dropping its output significantly compared to the other, for which the comparator circuit detects and sends a wake up signal to the arduino where another sensor would confirm the presence of a car and send a radio signal to the master node
Run the inputs to the Arduino as you would to the discrete comparator. You'll need to insure neither goes above Vcc or the inputs will be damaged.
@ShermanP's post #4 still applies.
I'd build a test circuit to find out if this will work. Connect the voltage dividers as you would if the comparator was in the circuit and measure the DC voltage at the taps when the panels are shaded/lit.
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