Giant bulb VU meter


The latest Inventgeek project is a 12 outlet control box. They decided to demo it using a giant bulb based VU meter. The control box has 12 individual outlets hooked up to two layers of six solid state relays. [Jared] notes that SSRs can be very expensive, but he purchased his on eBay for ~$10 each. Wiring and installation on this project is incredibly clean and they plan on using the control box for future how-tos. The simple audio circuit used for the VU is based on the LM3915. You’ll find full plans on the site or you can watch the overview video embedded below.


  1. macegr says:

    It doesn’t look like the VU effect is working at all…his explanation that the LM3915 is too fast doesn’t really explain the way it looks. It’s probably just wired wrong.

  2. JoeBlo says:

    Obviously the light bulb filiments are slower than leds, but it appears that they have it set to dot graph instead of bar graph. The green ones should remain bright while the yellow and red are coming on.

  3. jayson anders says:

    Yep, dot for sure. but the yellow bulbs are so bright they are messing with the camera a bit. reguardless. its a cool project!

  4. Stunmonkey says:

    SSR’s can indeed be hellishly expensive if purchased retail, but I have always had good luck finding boxes of new ssr’s left over from industrial surplus. Nice thing is they are usually only 3-10 bucks each and can usually be found in reasonable to even large numbers of matching units.

    There is no end of mayhem that can be accomplished with the careful abuse of a few of these!

  5. jayson anders says:
  6. alex says:

    i actually really liked the slurred responsiveness on the meter…. it gave it a little character rather than lights strictly going up and down

  7. I found some SSR’s for $4 each on eBay when I needed them for my smaller version of something similiar to this for my computer automated grow box.

  8. jayson anders says:

    Ok, i get it now. it looks like if he used somthing to control the sample rate he would get a cleaner look to it using standard lightbulbs. the circuit is very basic he used for the example.

    check this version out. much better…

  9. M4CGYV3R says:

    *maniacal Pee-wee Herman laugh* AAAAAh! Arduino! He said the magic word!

  10. agent420 says:

    solid state relays seem a bit overkill for driving lamps… it would be much cheaper and more compact to use plain old triacs…

  11. Glen says:

    Agreed i’ve seen circuits for this sort of thing in the past and they were always triac based. why use SSR if they are so expensive ?
    Imagine the price of trying to put together a proper VU set of say 10 strips all tuned to different frequencies.
    it could cost you a small fortune

  12. agent420 says:

    i also question the author’s comment on not using mechanical relays because they broke in a couple of days… he obviously did not use the appropriate relay for the task. in many cases, relays can be more rugged than solid state equivalents. mechanical relays also have lower contact resistance and capacitance, allowing them to better switch high current or high frequency circuits.

    point being, mechanical relays still have a place in modern designs and won’t be going away any time soon. good article here:

  13. agent420 says:

    While we’re on this subject, how about this spectrum analyzer that uses water pumps for a fountain like display. Probably nice for singing in the shower ;-)

    or air bubbles:

  14. JayOC1 says:

    I agree both relay types have there place. but it would be stupid to make this with mechanical relays with the rapid switching rates that a SSD can handel.

  15. JB says:

    Agree with agent420. I did something like this using triacs back when i was in college (long time ago). Cool project though. Nothing beats a VU meter using line powered high wattage bulbs :)

  16. draeath says:

    … not to mention the sound.

    Imagine the noise all those mechanical relays would make switching on and off so quickly?

  17. Doug says:

    When it comes to dressing up the display, a cabinet with rectangular, would be one way to go. For something different a cabinet constructed in an arc with segments rather than rectangular ones, to simulate an analog meter would be far out. mechanical relays would be reminiscent of tagging along with mom to the telco office to pay the bill, and hearing all that clicking coming from the back of the building. Yea I’m a grey beard.

  18. Bill Hates says:

    looks like a really complex color organ

  19. ahvv says:

    you could have used $2 1amp SSR’s that have have enough power for a 100 watt lightbulb

  20. The wiring IS clean. Good job guys – Just because it’s a hack doesn’t mean it can’t look professional.

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