In 2007 I purchased a new prop from Menards. It was marketed as a “Haunted Hedge”. It consists of a set of light up eyes, and a separate box that contains a motor with a wobble weight on it. When the prop is triggered it shakes the bush you place it in, moans, and lights the eyes. Out of the box the prop is supposed to be triggered by sound. Frankly I find the sound triggers unreliable, and in addition, there is never a re-trigger delay built in. This means, as soon as the prop is done making noise, it can be re-triggered by more noise. This makes it really easy for kids to stay in one spot triggering, and re-triggering the prop. The “Haunted Hedge” like so many Halloween props out there, comes with a “Try Me” button. Hold the button down and the prop runs, release the button and it stops. This makes for a simple method to interface the prop with my own controls. Read on for my solution.
I looked around on the net and found a circuit similar to what I needed here, but after reading it over I made a few modifications. The original design left the reset pin on the second timer floating, a state not recommended, my modified version corrects that. The original version also called for a mechanical relay to trigger the props. I was trying to go for a fairly small sized device, and I so I swapped the mechanical relay for a solid state relay, a CPC1510.
I had originally planned on powering my version off of 4 AA batteries, since almost all of my props use them. Because of this power change I had to change the value of the capacitor on the trigger line of the 2nd timer. In my actual implementation, I ended up switching back to the original 9V battery for size. I left the capacitor change in place, and it doesn’t seem to be having any adverse reaction. The new schematic is below.
I constructed the circuit inside a small project enclosure I bought at radio shack. I used a 1/4″ phono jack / plug to allow for easy attachment, and detachment of the external trigger switch. For triggering this prop, I will be using a mat switch I picked up years ago when the library disposed the old security gate system. The connection to the prop is made using the “Try Me” buttons own 2 pin 2510 Molex connector.
After construction was done, I set it up and I am happy to report it works perfectly, not a single problem with it. It survived it’s first Halloween night working perfectly. I’m a little shocked to be honest. 🙂
I have included my schematic file, and a PCB file for use with ExpressPCB. As of this posting, I have not actually ordered the board from ExpressPCB and cannot guarantee that it is correct. If you use these files, or find the timer useful, comment below please and let me know.
John's Musings 