While these little dudes don't come under the heading of 'home repair', I thought I'd mention them.  Remember all those fancy electronic gadgets and things in the old TV show 'Mission: Impossible'?  Well, while certainly much of that was just Hollywood being Hollywood, much of it was also quite real. 

Let me present a few scenarios to put on display how cool it is to control the electro-mechanical realm: 

I used to live in a fairly rural area, and I owned a real expensive stereo set.  As such, I wanted to install some kind of burglar alarm.  I'm a big fan of actual deterrence, though; deterring them from entering in the first place, so here's what I did:

  

The property was fenced, with two small gates across the driveway.  They're very common, with the little spring-type latch in the middle.

  
They're also metal. 
  
I cut up a plastic flower pot and placed the pieces of plastic between the gate hinges and the post, isolating the actual gates from ground.  I then ran a wire from each gate underground up to the house.  A tiny 1-volt current ran through them, keep a tiny relay closed.  Basically, the gates were acting like a big switch.  Should someone open the gates, the relay would open, thereby sending current to the rest of the alarm system.   
  
Most people, at that point, would have a bunch of big flood lights go on — but that would be telling the intruder that he'd tripped the alarm by opening the gate.  A mistake he's not likely to make the next time. 
  
Using a "delay-relay", I waited 15 seconds before turning on the floods.  This way, he's silently sneaking through the gate, down the path, when suddenly... FLOODLIGHTs!  The impression you get is that you just tripped a laser beam, or set off an ultrasonic alarm.  The gate is long behind you and forgotten. 
  
This person will probably not be coming back. 
 

I lived for a while in an uninsulated loft that got freezing cold in the winter.  Twenty minutes before bedtime, I'd crank up electric blanket to 'Cremate', then jump in and turn it down to low.  I'd usually get up in the middle of the night to hit the bathroom, and I'd jump back in bed and be just dying to turn the electric blanket up — but you can't, simply because you'd have to stay awake for 10 minutes in order to turn it back down.  So here's how I solved this mighty poser:

  

I went to the electronic store and bought a book on simple wiring diagrams and a bunch of parts, such as various sizes of resistors and capacitors, some 555 timer chips, some little testing blocks where you can plugs components in and test them, and some PC board for the final project.

  
The 555 timer chip activates after a certain period of time depending upon the values of the resistor and capacitor used in the (very simple) circuit. 
  
So, I wired into the electric blanket's control and had a relay bypass the control setting.  When the relay was on, the electric blanket was on full.  The relay was controlled by the 555 timer chip. 
  
I'd wake up, hit the button and the circuit would turn the electric blanket to 'High'.  I'd come back from the bathroom, jump into bed just as it was warming up, and drift happily back to sleep.  A few minutes later, the timer chip would activate, the relay would open, and the electric blanket setting would go back to whatever I had it set to. 
  
What price, bliss? 
 

How about making something operate by remote control, but on the cheap?  Back in the Dark Days of 8mm movie cameras, I was into wildlife photography.  The movie camera had a jack where you could plug in a wire and operate it by remote control, but I wanted to be able to operate the camera much further away, and wirelessly.  But nobody sold "wireless movie camera remote controls," of course, and it would have cost of fortune if they had.  So here's what I did:

  

I cruised into Radio Shack and bought one of their cheapie remote controlled cars.  I also bought some of their empty 'experimenter's' boxes, as well as some batteries and battery holders.

  
I disassembled the car down to its basic parts.  I found the wires that were being activated when the remote control button was pressed.  In place of the car motor, I used a small relay.  When activated, the relay would close the connection to the wire leading to the camera and turn it on. 
  
I jammed the guts of the transmitter and receiver into the two boxes, used real telescoping antennas instead of the cheap car stuff, and stuffed in a bunch of batteries so nobody would run dry. 
  
Sucker reached for half a mile! 
 

I was once living in a house with a nice landlady, and suddenly somebody started stealing our morning newspaper.  Rather than get up a 5 AM to try and catch the guy, here's what I did:

  

Late the night before, I took an 'unopened' newspaper and placed it on the front doorstep, where the paper was usually left.  I figured I had a 50/50 chance he'd grab mine.

  
I attached an invisible piece of fishing line to the newspaper, which ran under the front door and was attached to a small piece of paper. 
  
The piece of paper was all that was standing between two relay contacts touching each other.  The second the newspaper was picked up, the piece of paper was yanked away and the relay sent a 'go' signal to my 3-million-watt flashgun for my camera which was conveniently placed in the front window facing outwards. 
  
For one split second there, in the still of the early morning dark, with his trembling hands greedily clutching his prize, it must have looked like the sun blew up. 
  
Needless to say, he... well, needless to say. 
 

Another 555 timer chip story.  I had a neighbor who was a terrific guy, and we'd play table games all the time, like dominos, cards and Scrabble — but jeez, was this guy slow.  So I did what any clever gadgeteer would do:

  

I experimented with different resistor and capacitor values to arrive at 1, 2, 3 and 4 minutes.  I ran them through a selector knob on the box and labeled them.

  
On the box I put an amber light and a red light.  15 seconds before the time was up, the amber light would start slowly flashing.  When the time was up, the red light would go on and the player had to make a play or pass.  He then hit the button on the box to start the timer over again. 
  
That solved that little problem.

  
I guess the overall point is that one should take control of one's life, given the tools.  And many people simply don't know these great little tools exist.  Here's a brief description of the basic parts in the gadgeteer's universe: 

Relays are small electro-mechanical devices that are basically switches for yet another device.  Where they differ from a 'switch' is that the part that turns them on and off is independent of what's going to the thing being powered.  That way, a small 6v relay can operate a big 120v appliance, because the contact points are big enough to handle 120 volts.

  

Delay-relays, the old type, looked like the old vacuum tubes, with a set of contact points inside that were either normally open (circuit broken) or normally closed (circuit made).  When juice was applied, the arms of the contact points heated up over a specific period of time and eventually broke or made the connection.  Newer delay-relays are digital, where you just set the time on a dial.

  

Gearmotors are small motors that have a built-in gearbox so they can spin around fast and have a fair amount of power, but the actual axle is turning slowly.  If you turned to your computer and said, "Close curtains, please", the computer's voice recognition system would activate a small gearmotor around whose axle the curtain cord is wound.

  

Solenoids are small devices in which a plunger moves when electricity is applied.  A classic example are doors where somebody has to press a button to unlock them.  That big BZZZT sound you hear is the solenoid pulling back the plunger from the door jamb.

  

Photocells react to light and dark.  Parking lot lights that go on at dusk are controlled by photocells.  They can also be hooked up to relays, of course, so if you wanted something to operate when it got light or dark (inside or out), that's how you'd do it.

  

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