Audio activated switch/lightning machine…CHEAP!
I spent quite a while looking for a switch that would activate whenever it got an audio input. I found several that used one of those cheap microphone inputs, but nothing that took a line level input. You really need a line level input so you can send the output from a CD player, the output from an audio mixer, Tape Deck, computer sound card or just about any other source.
You don’t want other random sounds setting off your prop like the sounds from other props, or noises made by TOTers. You can use this method to set off props or synchronize lightning to thunder sounds. Even have the lightning first followed by the thunder a second later. (That’s what I do) You can use this to control any size prop with any power requirement. I’ll show you how.
The first thing you need is an LED VU meter kit. If you buy a stereo version, it will give you 2 controllers. For this illustration, I will show the mono version. This will make 1 controller.
I built several and mounted them all in one project box from Radio Shack which gives me control over 6 separate props in one box.
Let’s get started. Buy the kits you need. The mono kit looks like this:
It is kit #CK-104 http://www.canakit.com/5-led-vu-meter-kit-ck104-uk104.html
Converting this kit is REALLY simple. Build the kit according to the instructions except where it comes to the LEDs. Here’s the part I can’t remember, and the ones I built are all packed away at the moment. I forget which end is the Low volume end and which is the high volume end. Meaning which LED lights up first with the lowest volume level and it goes up from there. From memory I believe it goes from right to left, but I may have it backwards. The easiest way to tell is to put long wires where the LEDs normally would go at each end. Making sure to keep the polarity right, hook an LED to each set of wires and run the kit by putting an audio source to it. The LED at the low end will light first with the quietest sound, and the one at the high end may not light at all unless you are really blasting the input. Then you will know which is which. I also actually do hook up the second relay in the series just so I have visual indicator that shows me when the switch is ON. I mount the second LED on the outside of the project case where I can see it. You don’t need to do this part, but I like to have that visual cue.
Once you have done that, cut off the wires at the high end leaving the long leads at the low end in place. The wires at the low end are going to connect to the control wires of a solid state relay that looks something like this:
Again, be sure to observe the polarity and hook the two leads that would normally have gone to the first LED in the array to the control leads on this solid state relay. (The bottom two leads on the Relay). I use this particular brand, but there are many variations to it. You can choose to buy solid state relays that can switch up to 10 amps or more or as little as 2 or 5 amps depending on your application. You can find these all the time on eBay. Just type in “Crydom solid state relay”. The ones I use will switch on when the control voltage is between 3 to 30 VDC. The one pictured takes 3.5 to 15 VDC, but that would be fine as well. I forget the exact output voltage that goes to the LEDs, but it is in the range needed to run these Solid State Relays. Here are the Specs
for a Crydom Solid State Relay that will work. You can of course use other brands with similar specs if you wish. Just find the best deal.
You will need a power supply to run the VU meter Kit. I used a 9VDC supply and it was fine. It can use a voltage range from 4 – 14 VDC at 100mA. If you are going to run 2 kits from the same power supply, make sure it is at least 200mA. 3 kits/300mA and so on.
The solid State Relay (As far as I can tell) Only Switches AC voltage. If you want to turn on or off a DC powered prop or speaker wires to turn on or off a sound or strobe light control wires (like I do) to control a lightning effect, then simply buy a standard Relay with a 120VAC coil similar to these on eBay HERE
. Let the solid state relay turn on and off the standard relay, and use those contacts as a switch for whatever you want to control. For DC powered props, you can use a wall wart power supply that plugs into 120 VAC and provides you with the proper DC voltage and switch the power that goes into that wall wart on or off with the solid state relay.
Now for the part where I control the props and synchronize lightning and so on. You can split the output from your CD player or other source and feed half of it into this kit and the other half to the amplifier or amplified speaker. That would work….BUT…here’s the problem:
If you want a prop to be activated or lit up or to do whatever you want it to do continuously while you play your sound effect, you may not get that result by simply playing your sound into this audio switch. If your sound changes in volume or has quiet parts in it, the switch will go off when the volume level drops below a certain point. In some cases, that may be the effect you want, but in others, you may want the prop to be activated the whole time that the sound is playing or maybe even longer.
Here’s how I handle that. I use audio editing software to create my audio files. I use Sound Forge and Adobe Audition, But Audacity should work fine for you, and it’s free. I create a stereo sound file . Actually, I should say 2 track because the exact same sound is on both the left and right channel. Dual Mono is probably more accurate.
If you want to have your prop react exactly to the variations is the audio file you create, simply send one channel to the VU meter kit that you modified, and the other channel to your amp and speakers.
If you want the prop to turn on for a pre-determined length of time no matter what your audio file does, then you need to create a special audio file. I use a constant audio tone that you can download HERE
(You may have to right click on that link and all other sound links and choose "save target as' to download it)
I have that run in one channel for as long as I want the audio sensitive switch to keep the prop on. The other channel is the sound that I am sending to the amp and speakers. You can download an example of the file I made HERE
. That file is one I use for a banging coffin. I have a motor inside a full sized coffin that is half buried in the ground. There is a red light and a speaker inside that coffin. I want the sound to play, and the motor and light to be activated the whole time, banging the lid slightly up and down while the red light is on. I want the light and motor to stop just before all the sound trails away. As you can see in the audio file I created, the tone starts just after the initial sound, then stays constant until it shuts off a few seconds before the last sounds trail off. Since the volume level of the sound effect I made goes up and down a lot, the switch would have turned on and off several times which was not the effect I was looking for there. Using different audio on the two tracks solves that problem completely.
To create the effect of lightning flashing before the thunder I create another special audio file for each different thunder crash sound effect I have. You can download one of these files HERE
to see how I did it. Another way to do this without using the 'tone' method would be to shift one of the channels of audio a second ahead of the other. Send the channel that plays first to the switch, and the duplicate channel that is slightly delayed to the amp and speakers. Then your spotlights and/or strobes would flash in the same pattern as the sound, but would happen a second before you hear the sound. If you were to play a track like this in headphones, it would sound like an echo, hearing the sound first in one ear, and then a second later in the other ear. You can download an example of this audio file HERE
Again using tones, I decide when I want to activate the prop, in this case the audio sensitive switch is controlling a relay that switches on 4 large 1000 watt strobe lights which I use for lightning. The other channel of the audio file goes to my 950 watt amplifier and speaker which is in a second story window in my house. I start the tones about a second before the sound effect starts and use several short bursts to simulate real lightning, rather than just having the strobes on constantly. This will work just as well if you are using bright spotlights for your lightning instead of strobes. You can control the spotlights directly from your solid state relay without having to use a secondary relay.
Anyway, I hope I have explained this all well enough. If you have any questions, don’t hesitate to ask them here.