How to build a time delay circuit

Written by cassandra tribe
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How to build a time delay circuit
Time Delay Circuit Using a 555 Timer (

A time delay circuit is a programmable circuit that provides a delay in signal between your input source and output message. Time delays are used in everything from audio electronics to security electronics and computing. Building your own is an excellent way to learn more about the complex possibilities of circuits, once constructed, you can experiment with the effects of various time delays on the actions you are trying to initiate with your electronic device.

Skill level:

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Things you need

  • 555 Timer
  • 470K ohm ¼ 5% Resistor
  • 5 M ohm variable resistor
  • BC556 PNP Transistor
  • 22uf/25V Electrolytic Capacitor
  • breadboard
  • jumper wires
  • 12 volt battery

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  1. 1

    Place your 555 Timer on your work surface so the connection labels on the body are clearly visible with the output connection pointing to your right. Transfer the Timer to the centre of your breadboard. The edge of the breadboard that is away from you is considered the "top." You will notice that the "top" and "bottom" of your breadboard have a series of rows of holes that are slightly separated from the rest of the board. In performing the following steps you will only connect leads into these strips when it is specifically called for to connect to the "top" or "bottom" of the board.

  2. 2

    Attach your input leads to the left side of the board, they do not have to connect to anything, this is just to hold the lead wires from your input in place. Push your input lead wire into one of the holes on the board nearest your input. Connect the wire lead from the RST connection of your 555 Timer to the board. Now, using jumper leads or a piece of wire, connect both of the holes that you used to attach your RST and input. This forms a circuit path between your input and Timer.

  3. 3

    Attach one lead of the 470K ohm Resistor to your input connection by inserting it into a hole in your breadboard and then using a jumper wire to create a "bridge" between the two. Connect the opposite end lead of the 470K ohm to the board.

  4. 4

    Join the lead of your Resistor that is not attached to your input to your Transistor using jumper wires to form a bridge. Consider the edge of your Transistor that is away from you the "top." Use jumper leads to form a connection from the top of the Transistor to the CTL connection on your 555 Timer.

  5. 5

    Using jumper wires, connect the bottom of your Transistor to your 5 M ohm variable Resistor so the Resistor is located beneath the Transistor and the body of the Resistor is pointed towards top and bottom of the board (like a needle on a compass that is pointed North and South).

  6. 6

    Connect the bottom of your 5 M ohm Resistor to the bottom strip of your breadboard.

  7. 7

    To the right of your 5 M ohm Resistor, oriented in the same direction, attach your 22uF/25V Electrolytic Capacitor to the board. Make sure your Capacitor is attached to the board only and not to the Resistor. There is a (+) mark on one end of the Capacitor. That mark should be pointing toward the top of your board.

  8. 8

    Form a connection from the TRIG lead of your 555 Timer to your Capacitor. Then connect your Capacitor to the bottom strip of your breadboard.

  9. 9

    Join the connections that come into the top of both your Resistor and your Capacitor. You are not connecting the Resistor and Capacitor, only the wires that lead into them (from the Transistor and the Timer).

  10. 10

    At the top and bottom of your 555 Timer are leads. The marking for these leads is "GNDVCC." The "CC" part of the marking should be at the top. You will connect the lead from the top of your Timer to your 12 volt battery source. Form a connection from the bottom of your Timer to the bottom of your breadboard.

  11. 11

    Attach leads from the THR connection on your Timer into the lead connection you formed from the bottom of the Timer into the bottom of the breadboard.

  12. 12

    Lastly, from the right side of the 555 Timer you will connect one lead to your output, this will be the source you are controlling with a time delay. This connection is labelled OUT on the Timer. The remaining connection, DISC, can be run to a potentiometer to make it easier for your to experiment with various parameters in time delay.

Tips and warnings

  • Once your time delay circuit is built, test several different parameters with the time delay and then solder all the connections you formed with jumper wires.
  • Always test a newly built or experimental time delay circuit on input and output sources that are expendable in case there is a problem and the sources are damaged in the fine tuning of the circuit.

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