93 lines
5.0 KiB
Plaintext
93 lines
5.0 KiB
Plaintext
Chuck #1 @9811
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Mon Sep 24 20:51:52 1990
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How to make an in-use light
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from the Night Owl AE
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This file describes the operation and construction of a device that will
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signal whether or not an extension of a particular phone line is off-hook. It
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does NOT indicate whether or not a phone is being tapped, and will light
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whenever any extension is picked up.
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The principle under which this device operates is that there is a voltage
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across the red and green wires of the phone line (the other wires are rarely
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used) that drops significantly when an extension is lifted. Though this
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voltage can be used to power a light on its own, the light would have to be of
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a very low power consumption in order not to keep the phone off-hook, and it
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would only light when the phone is on-hook.
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A simple way to get around the above problem is to use a low current relay.
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Radio Shack sells some nice 12VDC SPDT relays that work well for this purpose.
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Don't buy the reed relays or the subminis; though you want a low current coil,
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you also want the contacts to be able to handle a decent current. DPDT
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(double pole, double throw) will also work, you just won't use the other
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contacts.
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For a 12 volt coil, the voltage will have to be dropped so that the relay will
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function properly. The proper resistance is around 10K ohms, but it is best
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to use a 5K ohm fixed resistor and a 10K ohm variable (standard values, any
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combination that can cover the 10K range will work fine). Adjust it to
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approximately 10K, or halfway for the combination above. Connect the
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resistors in series with the coil, and we'll adjust it later.
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Due to the nature of this device (or rather, its simplicity) it will operate
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without having to be plugged into a phone, or vice versa. In other words, you
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can plug it directly into a jack anywhere, and it'll work. You'll want to get
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a modular plug that terminates in spade lugs for this purpose. Connect the
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green wire to one side of the coil, and the red to the resistors (so that it's
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all in series). If you don't have an extra phone jack, then you will want to
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a) buy a Y connector so that two phones can be plugged into the same jack, or
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b) get another phone jack and install it in the same box with the in-use
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light, so that you can plug a phone into it. Just connect the spade lugs to
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their respective colors.
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For the light itself, you can use almost anything. Even a tiny light bulb and
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a battery will work fine, but after about 5 hours of phone use, you'll have to
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replace the battery. The best thing to use is a neon bulb powered by the 110V
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power available most places. Buy ones with dropping resistors, or use a 220K
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resistor for dropping. You should also get a panel lamp assembly to keep it
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steady and make it look pretty. Since the current is relatively low, you can
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use almost any power cord, or sacrifice an old extension cord. Connect it in
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series with the NC (normally closed) contacts of the relay (in series with the
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dropping resistor, of course).
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Your circuits should now look like this:
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/
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--------RED----!---- 5k --- 10k -------O O-------------------!-----110V
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/ | |
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coil NC /
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| |
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-------GREEN---!-----------------------O O-- bulb --- 220k --!-----110V
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Make sure that the phone circuit (left) and the lamp circuit (right) are
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totally 100% separate, and in no danger of touching. Use wire nuts for all
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connections in 110V that are not to a terminal post, and tape them. For all
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wires that are exposed, use electrical tape or shrink-wrap tubing to insulate
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them. Glue the relay to the box or mount it on a stable PC board.
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If all looks well, hook it up. It should work immediately, but there are
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three things that can go wrong: 1) The relay keeps the phone off the hook.
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To remedy this, lower the resistance until it doesn't. If you can't lower the
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resistance enough, then you are using a resistor with a high current coil and
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you'll have to get one with a lower rating. 2) The relay won't close. The
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solution for this is the same as number 1. 3) The relay stays closed. Raise
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the resistance with the phone on hook until the light goes off.
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When all is working, the lamp should be on when one or more extensions are
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off-hook, and will be off when all extensions are on-hook. It will blink when
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the phone rings.
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This is a parts list:
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1 box. Make it a nice one, preferably one with feet.
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1 phone cord with a modular plug at one end and spade lugs at the other.
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1 phone jack or Y adapter (optional).
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1 power cord or old extension cord.
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1 low current coil relay, double throw.
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1 5K fixed resistor.
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1 10K variable resistor.
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1 neon bulb with dropping resistor.
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1 panel lamp assembly. Some come with bulbs.
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That's it. You may trade this file however you wish.
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1N ........................ . ... ...-.... 1200 N81N ........................ . ... ...-.... 1200 N81N ................... |