I was looking at a catalog, and they had a home alarm kit with a key pad.<p>In this neighborhood, an alarm would not be any use, as no one would hear it.
I do have a problem with missplacing keys, however. I like the looks of the thing, and I was wondering if it would be possible (long time down the road) to instead of making an alarm, making it into a keypad for a lock with a deadbolt, where the quarter inch deadbolt would be moved by the project.<p>I imagine, however, that a quarter inch deadbolt would be to much to run off a single nine volt, or that I would have to replace the battery offten. Would the bolt have to be run off a transformer from the house current, and the keypad off the battery? If the power goes out, am I stuck outside in the rain?<p>Thanks
If I put my finger in this light socket, will it straigten out my hair?
Good questions, Steven. Solenoids are rated by their voltage (and consequent current), length of stroke, pulling power (usually in ounces) and holding power (also usually in ounces). Since most home deadbolts have a one-inch stroke, it's out of the range for most solenoids to reliably pull as a straight bolt.<p>Years ago, I built an over-the-bed-rails toolbox for my runt pickup from wood. Rather than the traditional latch setup with exterior locks, I used eyebolts that extended into the interior of the box at the outer edge of the lid. Inside, two long pins connected by a long rail engaged these eyebolts. Outside, I pulled on a handle to pull the pins from the eyebolts, unlocking the lid. But to keep outsiders out, this handle that I pulled had a catch on it that ran into the plunger of a small solenoid. You had to push a button inside the door of the truck to engage the solenoid to pull the plunger out of the way of the handle catch. Didn't take much solenoid power for that since the pulling of the handle did all the work of unlatching the lock. But if that solenoid wasn't engaged, there was no way you were going to pull that handle past the solenoid plunger.<p>So, take that one step further. Figure out some way that you can modify the deadbolt so that there's a hand knob both inside AND outside the door. Put the solenoid inside the door frame where the solenoid plunger can engage a hole or notch in the TOP of the deadbolt latch. Grind the top lip of the latch so that it will push the plunger up and engage without you having to electrically pull the plunger back when you lock the door, much like the regular doorknob latch works against the strike plate.<p>As far as power going out? That's why you keep an emergency key to the back door in every vehicle and at a trusted neighbor's house.<p>The door locks at a U.S. Naval Security Activity operational building was a monster of a thing designed to keep the door from being rammed in. It was a BIG latch and was operated by an electric motor rather than a solenoid. A bit of an overkill for a household door!<p>Dean<p>[ January 17, 2003: Message edited by: Dean Huster ]</p>
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).
You Can always build a Ratchet Solenoid. <p>What it does is it pulls back on a solenoid one stroke at a time, pulling on a gear one tooth at a time, and at the end of each cycle it is controlled by a power switch turning it off, and with spring, it returns the solenoid plunger one more time to grab another tooth and move it just a little at a time, to then another ratchet device that pulls on the actual “throw” of the dead bolt, again one notch at a time. <p>Kind of like a clock inside, but instead of a pendulum the solenoid pulls and resets automatically on the gears, which in turn move the plunger of the dead bolt very slowly, perhaps a 1/16 of an inch at a time. <p>Great leverages of pounds can be accomplished by large diameter ratchets wheels. <p>I have a very neet one of these units on all of my Gyros that pull a dead bolt like device that releases the cradle from the park position that is used to store the gyro for transportation. <p>Its noisy as it clacks away but with very little power, its cyclic motion edge the dead bolt device open one small step at a time in just three seconds or less. <p>Lots of force can be applied with very little current because in essence it’s a high gain winch.
