Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automaticly shorting circuit

  1. Apr 5, 2012 #1
    hi everybody. i need a circuit which will short 2 cables for 0.5 seconds every second. let me explain like this:

    (+2.4v) | | (0)
    -----------| |--------------
    | |

    in the ugly drawing above you can see two wires with a potential difference of 2.4 volts connected to a box. the box just represents the circuit that i want to make with your help.
    this box must have zero resistance for 0.5 seconds and infinity resistance for 0.5 seconds. so its like a pulsating current with 1Hz across this two wires. Can you guys help me with this ? i have circuit elements like resistor, capacitor, leds, transistors(only BDX53C, BD243C, TIP41C and BDX54C), and etc... The timing doesnt have to be so strict, 0.5s+-0.05 is fine. The current that will be drawn during shorting is not high, not higher than 100ma. I need the simplest and most efficient circuit that you know :)
  2. jcsd
  3. Apr 5, 2012 #2
    sorry about that drawing, it didnt come out like i wanted. here is correction:

    2.4v ----------------|BOX|--------------- 0
  4. Apr 5, 2012 #3

    Put BD243C npn transistor across those cables(collector to 2.4V side). Use a 555 timer for sending square wave pulses to base.

    http://pokit.org/get/img/107e57d75a27c44c658941c60d53b2b7.jpg [Broken]

    Here are the values for 555 timer.
    Last edited by a moderator: May 5, 2017
  5. Apr 5, 2012 #4
    You could always drive a little reed or telecom relay if desired. Those are pretty quick and will give as close to a dead-short as you can get.
    The 555 timer circuit above should be able to drive one of those without issue.
  6. Apr 6, 2012 #5
    If you suspect you may need to alter timings etc and dont mind spending a few extra pounds you con get a simple logic controller with relay outputs, a basic logic programme will give you an unlimited output function with easy alterations and time scaling down to the thousands of a second.
    You can get a starter kit and i promise you, you'll have programmed it within the hour even with no experience, the best thing is you can save the programme and load a new one for your next project.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook