I am creating a propane "regulator" which allows the user to connect a speaker output to control a valve (0-10V max:0.185A) which opens more with higher voltage.

Here's a video of it operating (WARNING VERY COOL).

This is the valve.

It also has a bypass past the valve to allow a steady flow when no music is on.


The valve opens the most with high bass input because the voltage is higher across the subwoofer input line and the valve is opened for longer because the signal is lower frequency giving a very nice bass effect. The valve opens on either positive or negative signal but does so quickly (but not as fast as the 20-20k hz signal it's getting so I also installed a Rectifier so that the valve doesn't have to adjust open-to-close-open it can just stay in the open state as long as the wave is still occurring).

I'd like to:

a) make it more sensitive to other frequencies (I'm getting a different valve that allows me to vary the gain of the valve). But other ideas are welcome.

b) add some way to increase the voltage to just the valve so that the music volume or bass gain doesn't have to be high in order to get a good effect of propane release. I think that ideally a user might be able to adjust a potentiometer that would control the gain or even adjust it with an app on their phone. One concern is that the voltage doesn't get over say 12V or it might damage the valve, so I assume I might need some sort of regulator in case the settings are off.

c) know which type of input I should use for controlling the valve/circuit to make it most universal for users to hook the system up to any stereo system they like. I'm currently just using the spring clips for speaker wires but I was thinking that some way to hook up to the preamp output signal would be great (but that's very low voltage and would certainly require some voltage multiplication or something)

I've filed a patent over the basic structure in case anyone's worried that this would constitute public disclosure (I love this community for being so happy to help by pointing out things like that in the past).

Thank you in advance. This has been a stumbling block for me.

  • 1
    \$\begingroup\$ First of all you get my +1 because your project is awesome. Then I'd suggest you to contact a professional to help you because of two reasons: 1) "I filed a patent" -> you probably want a product, new difficulties will rise and 2) your question is big, meaning that a full answer will require hours of design to make a proper thing. It's not likely someboedy is going through all that just for fun. I suggest you think of some specifications and contact some tech guy, also around here. \$\endgroup\$ Commented Aug 7, 2014 at 22:07
  • \$\begingroup\$ Thank you! I'm happy to do more of the leg work, but this question is just to find out which type of components to look at and to give me a good start on what to adjust. Basically my focus on what type of Voltage Multiplier (or another component I don't know about) to look at and play with. Thank you again. \$\endgroup\$
    – Ryan Ellis
    Commented Aug 7, 2014 at 22:10
  • 3
    \$\begingroup\$ So you patent a Ruben's tube/Color Organ? Lol \$\endgroup\$
    – Passerby
    Commented Aug 7, 2014 at 22:34
  • \$\begingroup\$ A Ruben's tube operates totally differently, is more expensive, and is less safe. I know, because that's how this started. \$\endgroup\$
    – Ryan Ellis
    Commented Aug 7, 2014 at 23:04
  • \$\begingroup\$ A Ruben's tube is acoustically coupled. This is electronically coupled. And you simply took a color organ, and replaced the bulb/led with a solenoid. What's the difference between this and a music-controlled relay? Or any christmas lights audio controller? There is so much prior art that your patent can be quickly invalidated, or you can be sued for infringing on other patents. \$\endgroup\$
    – Passerby
    Commented Aug 8, 2014 at 1:38

1 Answer 1


You want something basic, have a look below.


simulate this circuit – Schematic created using CircuitLab

That's just a block scheme I believe you already had in your mind, it's there only to help me tell you my ideas.

Let's start from the valve drivers. Of course you can have as many as you want. These little guys accept an input say from 0 to 5V or whatever is reasonable and scale it to the valve dynamics. They also adapt the impedance, i.e. that the box driving them will not need to source current: that's the driver's job. Inside these boxes there is an amplifier. I've just looked your valve spec, the current is not that high, you might get away with just an operational amplifier. Just look it up. The drivers may (and should) include some limiting (and safety!) devices to be extra sure to keep the output in the valve range and above all to be sure that if the system fails, it fails gracefully, i.e. you don't want the valve to be wide open. The driver will need some high voltage, somewhat high current power source (marked PWR).

Now to the bigger guy. You have only a line in input (you can hook it to the headphone output of any device) in addition to the power input (marked low voltage). The filter bank takes your signal, processes it and produces the voltages needed for the valve drivers. What happens inside the filter bank? You tell me. You may take a portion of the signal with a bandpass filter, reveal its envelope, multiply it for a fancy gain then send it to valve one. Valve two may be wide frequency driven, but only from signals above a certain treshold. Valve n may be driven by whatever, and so on. That's part of the specification. What is inside the filter bank? Well, somebody will eventually tell you. You might implement all the functionalities with analog filters and op amps, but especially if you want it iOSomething powered you better throw in a microcontroller, that will require an ADC to read the line in and some knobs and a DAC for the analog front end. That is the though part and nobody around here will tell you more than bandpass filter or envelope detector. That is huge, believe me. For the records, the filter bank is the thing with all the fancy knobs and lights on it.

Yes, filter bank is used in the broad sense of the word.

  • \$\begingroup\$ A few options for the "filter bank" described in this answer would be: 1. Something like the filters + envelope detector used in these glasses, 2. An MSGEQ7 IC and a microcontroller, 3. A microcontroller with an ADC and sufficient power to perform an FFT and envelope following algorithm. There's plenty of other sound driven projects around to influence you! \$\endgroup\$
    – LeoR
    Commented Aug 8, 2014 at 10:38

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