Hi,
Posted back on 5/3/05 on the DIY kit #8 light alarm. Got four of the things for $6.60 each and built three of them. Got them from:
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they are out of stock now at that place. Might be available elsewhere. Yes, I know there are cheaper alternatives out there but I liked the clean off/on phenomena idea using the photoelectric cell. Just a little report as this BAR was able to get some use out of them and had some weird experiences with the devices. First off, used an N battery holder to cut down the size of the 9V power source. Second, I used Devcon plastic epoxy to glue the battery holder to the back of the circuit board. Setting the setpoint can be very sensitive and I have one unit that will not shut off completely. In the dark, it gives 5 beeps then pauses. When exposed to light, it beeps continuously. I use it in a radio rocket with a transmitter and I can hear when the recovery system has deployed by that change in the beep pattern! The other two shut off in the dark and come on in the light. Haven't built the fourth yet. I did use some N batteries that were partially worn down from using in some radio bugs I have been experimenting with. Using 12V didn't matter except I think it might have made the setpoint more sensitive. Thus the reason for using partially run down N cells. :) I suggest that one tapes in the battery for any beeper that uses an N battery holder. The importance will be apparent to the reader. The board has two holes where I tied some Kevlar for a lanyard by simply knotting the ends. I had threaded a number 3 Laker ball bearing snap swivel to the Kevlar before knotting for allegedly easy transfer to different models. These Laker swivels are 3 for a dollar so are not cheap. Out of three launch sessions I have lost the beepers off of the models THREE times! Four times if you include the ripping out of the plastic connection on the payload bay in a small model. (That one really doesn't count as a swivel failure.) Each time the snap swivel failed at the snap. Because the battery was taped in, the units free fell into the grass at the driving range I use to launch and I simply walked over to the area where I thought the model ejected. I found the beepers beeping away and were none the worse for wear after a free fall of between 700 and 1000 feet. I did recover the models too. I have since decided to use a long enough lanyard so I can thread the unit to the screw eye with a single slip knot. I have not had a loss since and I credit it with saving my Super Nova Payloader. Used an E30-7 today and the wind carried it to some tall grass. I had to sprint to get a visual fix and decided to walk straight to where I thought I saw it go down. Kept walking and started hearing the beeper. It was about 50' to my left from where I thought I saw it go down. Boy did that really help expediting the recovery. The other times the models landed on field and I really didn't need the beepers. The lesson here is to just use a slipknot to secure the unit and put tape around the battery. I did have the mass rip the plastic eyelet out of the payload bay of a small Nova Payloader so I wouldn't use it in a small model unless you modify the payload bay with a small scrap of plywood and epoxy so you can use a standard screw eye and epoxy it in. Have since done that to that model. One other suggestion is, if you have the room in the body tube, make a small roughly 3/8" cone to wrap around the Piezo. It acts as a megaphone effect and it sounds louder. This can be done with any beeper and I have done so with some of the simple screamers you can build from plans found and the Essence site. You can experiment with different size cones by cutting and forming the cone and holding it on the Piezo. When it sounds the loudest, CA it together and then to the Piezo. Check your body tube size first as with the cone you can't use it in the smaller body tubes. Wish I didn't have to find all this information out myself but it was fun doing so. Hope someone might find this useful.
Kurt Savegnago