Tuesday, June 18, 2013

Shotgun Bulb

Last week I went to visit my old high school auto shop. They where mounting an electronically (or handcuff key) locked shotgun mount. For some idiotic reason this mount which was designed for cars was also designed to take 5 volt DC power (cars use 12 volt DC). To reduce the voltage across the solenoid in the mount they had mounted a resistor in series with the mount, however after they did this the solenoid no longer actuated. I thought to check the resistance on the solenoid and found it to be about 4.5 Ohms, the resistor they were using was a 1 kOhm resistor. What this meant was that there was almost no voltage or current across the solenoid. I did some math and determined that what they needed was a 10 Ohm resistor to get 5 Volts across the mount. However 10 Ohm resistors tend to be far more pricey and bulky than regular resistors because they tend to have to deal with far more power than most resistors due to V=IR (so if the resistance gets smaller and the voltage stays constant much more current is drawn), also we didn't have one. What we did have was an old tail light with resistance close enough for our purpose. So now whenever the switch is flipped to open the shotgun mount a light will turn on.

 The switch.

 The lightbulb on.

 Shotgun mount closed.

Mount open, it is designed so that you can simply flick the switch and pull the gun out.

If you ever wondered what was in a cops trunk. The red and blue lights flash whenever the trunk is open.

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