Hi,
I have a solar pump that has a built-in switch which one can set to which voltage it starts pumping, the power is supply by a 12VDC solar panel. I have managed to measure the voltage that the solar panel generates via a voltage divide (With help from this forum). Now I would like to know when the pump switches on and off, does anyone have any suggestion ? I suppose I could manually measure it, but I want to automate it, so if I change the start value in future it is automatically picked-up by the arduino.
I was thinking a measuring current, but I am not sure how to create such a sensor.
Hall effect sensor was my other idea, but I don't think that will work with DC.
It got me thinking, could I not use a relay, placed is series with the pump. When the pump switches on the relay should 'close', this will open the other circuit which I could supply with 5 V, then use a digital input pin on the arduino ? Or one of those opto-isolators ?
The pump uses the 12VDC from the solar panel. There is a dial on the pump which sets the voltage at which the pump starts. I have tried to get more information about the pump, especial the about the dial. One adjusts the dial to the according voltage that it must start and stop at. I suppose the dial is a type of variable resistor.
If you want/need to measure current, something like what Ran Talbott suggested would be excellent (although at $20).
If sensing on/off is sufficient you could try to locate the actual motor +/- terminals. A voltage divider (same as for measuring solar panel DC voltage level) across these terminals to an Arduino input pin will give you a high/low when motor is running/stopped. Note that this will only work if the motor minus terminal is permanently connected to ground.
It is also possible that the output voltage from the DC panel will drop/rise sharply (e.g. 1V or so) when the motor starts/stops. The ADC input you already have may allow you to detect these sudden changes. You would need to experiment with switching the pump on/off manually to see if it is detectable.
The key thing about the $20 board is that it measures mondo big Amps: the ones Sparkfun sells for $10 are only good up to 5A, and the 10-20A boards I've found elsewhere (e.g., phidgets) are even more expensive.
It's likely that a 12V pump will draw quite a bit of current, risking a burn-out of a lighter-duty sensor. And the Sparkfun board gives you a scaled voltage reading, which Gregg mentioned that he also wanted.
All in all, its rather spendy for volume production, but the cost trades off well against the hassle of making one or two at home.
I have been thinking about this and have come to the conclusion that monitoring when the pump starts and stop is wrong. What I should rather do is use the arduino to start and stop the pump, this will be a much better idea and moves the control of the pump to the arduino - where it belongs. So this will be my new path of exploration. Thanks to all who replied so far.