Wuben        
Results 1 to 10 of 10

Thread: Voltage trigger?

  1. #1

    Default Voltage trigger?

    Looking for some help with electronics. Iím trying to power a microcontroller with a solar charged super capacitor (and then power LEDs from the mc). Iíd 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!

  2. #2
    Moderator
    archimedes's Avatar
    Join Date
    Nov 2010
    Location
    CONUS, top left
    Posts
    13,386

    Default Re: Voltage trigger?

    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.
    ... is the archimedes peak

  3. #3

    Default Re: Voltage trigger?

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

  4. #4
    Moderator
    archimedes's Avatar
    Join Date
    Nov 2010
    Location
    CONUS, top left
    Posts
    13,386

    Default Re: Voltage trigger?

    Here is fine now, but if you get no response(s) , please remind me after a few days.
    ... is the archimedes peak

  5. #5
    Flashaholic* DIWdiver's Avatar
    Join Date
    Jan 2010
    Location
    Connecticut, USA
    Posts
    2,464

    Default Re: Voltage trigger?

    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.

  6. #6

    Default Re: Voltage trigger?

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

  7. #7

    Default Re: Voltage trigger?

    Quote Originally Posted by der View Post
    Thanks! I just ordered some. Iíll 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.

  8. #8
    Flashaholic* DIWdiver's Avatar
    Join Date
    Jan 2010
    Location
    Connecticut, USA
    Posts
    2,464

    Default Re: Voltage trigger?

    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.

  9. #9

    Default Re: Voltage trigger?

    Quote Originally Posted by DIWdiver View Post
    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.

  10. #10

    Default Re: Voltage trigger?

    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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •