I'm using the output of an op amp (LM308) with a low pass filter (R=4700Ohm C= .01 uF if that helps) to control a SSR (D2w203F) which is controlling a string of Christmas lights. I was wondering if there is anything better than a relay that I could use. I've heard SSR are bad when working with audio signals.

The goal is the make the string of christmas lights pulse to the bass of a song. The input is from an audio cable plug into an iPod.

PLEASE provide datasheet references to components used - RM.


Datasheet D2W203F 280 VAc, 3.5A, zero crossing SSR

Datasheet: LM308 opamp

  • \$\begingroup\$ Maybe instead use a similar design like this, goldmine-elec-products.com/prodinfo.asp?number=C4530 I built one years ago and used it with Christmas lights, no relays used \$\endgroup\$ – jsolarski Aug 3 '11 at 23:37
  • \$\begingroup\$ That's an impressively minimalist looking design! Looks like it uses a few passives for gate drives (maybe DIACs too?). @jsolarski says it works - Buy it !!! :-) \$\endgroup\$ – Russell McMahon Aug 4 '11 at 0:08
  • \$\begingroup\$ I really wish they would give you a parts list or schematic....here is one that uses an SCR(silicon controlled rectifier) electronickitsbychaneyelectronics.com/… \$\endgroup\$ – jsolarski Aug 4 '11 at 1:36
  • \$\begingroup\$ @jsolarski That's perfect! it is a shame they don't add the parts list. If you make that comment into an answer I would make it best answer \$\endgroup\$ – Mike Aug 4 '11 at 16:32
  • \$\begingroup\$ Let me do my research, and give a more complete answer \$\endgroup\$ – jsolarski Aug 4 '11 at 23:57

Instead of using SSRs or relays you can use SCRs (silicon controlled rectifier). Simple Color organ schematic reference site

Most of the kits out there use 106B1 SCR or a Teccor S2003LS1 you can find a another take on the design with parts list here

I have personally built one of these and had it running for years with Christmas lights with out issue. You can easily modify the filtering circuit to have different channels activate with different frequency.

just remember to use an audio isolation transformer to protect your audio equipment, it would be bad to send 120AC into your ipod or or stereo outputs

  • \$\begingroup\$ I really like this actually... Whats the difference between a SCR and a SSR? \$\endgroup\$ – Mike Aug 8 '11 at 0:01
  • \$\begingroup\$ From my understanding A SSR is more like a solid state switch, its either on or off, SCR controls the current, and is controlled by the gate, sort of like how a transistor controls DC current. This is as far as my understanding goes. \$\endgroup\$ – jsolarski Aug 8 '11 at 0:20
  • \$\begingroup\$ @Mike - The SSR most often has a triac (rather than an SCR) as switching element, but instead of controlling the gate directly there's isolation between driver and triac, and you drive a LED. For best results don't use a zero-crossing switching SSR, but a random-switching one. \$\endgroup\$ – stevenvh Aug 8 '11 at 11:03

Your SSR isn't switching audio, which it would be bad for. It is switching the AC power to the lights, so that's fine. Since you are apparently switching the power on and off rapidly, a SSR is a good choice.

You are apparently using a audio signal to control the SSR somehow. That's also fine if it's done right. It sounds like you're just feeding the amplified audio signal into the SSR input. That will turn it on when there are large positive peaks, which will very roughly make the lights come on when the audio is loud. There are better ways to detect loudness. To avoid switching the SSR on and off too rapidly (could cause lots of radio interference), you should be using zero-crossing SSRs. These turn on and off at zero crossings, regardless of when the input signal goes on and off.

Of course zero crossing SSRs might not give you the visual effect you want. You'd have to describe what you really want the lights to do as a function of the audio signal for us to suggest a good method.

  • \$\begingroup\$ Probably looking for the classic triac color organ. The advantaged of a packaged device might (only might, depends on specs) be better safety when working with mains power. This whole idea may get interesting with LED lighting taking over... \$\endgroup\$ – Chris Stratton Aug 3 '11 at 21:39
  • \$\begingroup\$ The SSR chosen is zero crossing triggered so has a maximum response rate of 120 Hz which makes it tend to be bass responsive OR saturated instantly by higher frequencies. Use of a simple RC input filter (series R to opto input, capacitor to ground from opto input) may provide enough of a low pass filter to respond mainly to bass, especially when combined with zero crossing switching. Datasheet D2W203F 280 VAc, 3.5A, zero crossing SSR \$\endgroup\$ – Russell McMahon Aug 4 '11 at 0:11

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