Voltage trigger?

der

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Looking for some help with electronics. I'm trying to power a microcontroller with a solar charged super capacitor (and then power LEDs from the mc). I'd like to switch the micro controller on once the supercap reaches a target voltage and then switch it off again when the voltage drops below another level. Would something like an mcp112 do this? Looking for a simple easy and efficient solution to this one!
 

archimedes

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Not sure if this topic is more about Flashlight or Non-Flashlight Electronics, rather than "LED" as such.

If you want your thread moved at some point, just let staff know.
 

der

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Sorry if I posted in the wrong place. Please feel free to move if appropriate.
 

DIWdiver

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Yes, that's exactly what an MCP112 is designed for.

You have certain fixed voltages to choose from, and no control over the hysteresis (difference between 'on' and 'off' voltages). If you need more precise control of the voltages, you can build your own with a handful of parts. The tradeoffs would be higher parts count, cost and current load.
 

der

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Thanks! I just ordered some. I'll let you know if it works!
 

MeMeMe

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Thanks! I just ordered some. I'll let you know if it works!

I think it will go poorly. Something like the MCP112 is designed for a rapidly increasing power supply that will stay well above the trigger point once it has passed.

Your slowly increasing solar supply will come out of reset, start draining the capacitor, and then assert the reset again ... not really what you want. You have several things you need to do:

- Hold the part in reset when the voltage is too low to safely operate (MCP112 can do this one function)
- Go to sleep when the voltage gets low (usually that function is built into a properly selected micro)
- Start operation at a given voltage (comparator)

You may be able to use the MCP112 to get the part started .. maybe, if the first thing that happens if you put the micro to sleep until it gets an interrupt on a pin that indicates the voltage is high enough, which you can do with a low power comparator or another power supervisor. Then you use a brown-out detect built into the micro to shut it down as appropriate.
 

DIWdiver

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Now that I think about your application a bit, why not turn on the LEDs when it gets dark and off when it gets light? With a supercap there's no problem with over-discharge, so what would you even need a micro for?

With your plan you'd likely waste a lot of power running the LEDs when it's still light out.
 

MeMeMe

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Now that I think about your application a bit, why not turn on the LEDs when it gets dark and off when it gets light? With a supercap there's no problem with over-discharge, so what would you even need a micro for?

With your plan you'd likely waste a lot of power running the LEDs when it's still light out.

Could do it just for a number of hours after dark, but we are assuming a general lighting application.
 

der

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Thanks to everyone who helped! In the end I lowered the clock speed of the microprocessor and ditched the voltage trigger altogether. Seems to work well! You can see what I made here - https://youtu.be/ON9UrY1VQQM
 
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