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I recently found an old part of a train crossing gate (semaphore) in the weeds and mud near a train crossing.

enter image description here

I cleaned it up, and want to make it flash when I get a notification, so I'll be using one of my Arduino Unos.

I have an old PC power supply that should do the trick for powering it, and it works, so I think I'll just wire the Arduino to control the power supply by switching it on and off using the on/off pins (14/15)

ATX Pinout

Anyways, would using the Arduino to rapidly (1-2 seconds) toggle the power for the power supply be safe or alright thing to do? Would it be over-taxing on the supply? It'd only flash until I clear my notification, though that could be hours' time, if I'm away.

jippie
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Austin Burk
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1 Answers1

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I'm assuming that your train crossing light uses 12V DC, but even if it uses some other voltage that your PC power supply provides, the same principle applies:

I would not switch the power supply on and off at a frequency of 1-2s. A PC power supply is simply not made to do that, and because of the self-test it performs which can take a few hundred ms.

Instead I would recommend that the power supply be continuously on, use the 5V output to power the Arduino, and the 12V output to power the flashing light through a relay or transistor which the Arduino controls. The current requirement of the bulb would determine whether using a relay or transistor is more practical, but if you need to use a relay, you will also need a transistor to drive the relay. Check out some other answers about switching a load on and off from digital output pins.

If you don't want to have a PC power supply running all of the time because of the noise, consider obtaining a different power supply which is passively cooled. Just make sure it can supply enough current for the flashing bulb. You can find dual output supplies that are 5V and 12V, or you can opt for a single rail with 12V only, and drop the voltage for the Arduino using a linear or switching regulator (buck converter).

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JYelton
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  • Also, be aware that incandescent lamps, unlike LEDs, have an enormous turn-on current surge, like 10 times steady-state. Depending on exact levels, your PC supply may get unhappy. – WhatRoughBeast May 10 '14 at 20:16
  • Thanks for the great answer! Not only did it contain a direct answer to the question I posed, but an explanation as to why it was so, and other alternatives to the situation I had. Time to take a trip to RadioShack! :) – Austin Burk May 10 '14 at 20:27