Long Delay Timer Circuit


Posted on Feb 6, 2014

This timer was designed mainly to switch off a portable radio after some time: in this way, one can fall asleep on the sand or on a hammock, resting assured that the receiver will switch off automatically after some time, saving battery costs. R1 and C1 provide a very long time constant. When P2 is momentarily closed, C1 discharges and the near ze


Long Delay Timer  Circuit
Click here to download the full size of the above Circuit.

ro voltage at its positive lead is applied to the high impedance inputs of the four gates of IC1 wired in parallel. The four paralleled gate outputs of the IC go therefore to the high state and the battery voltage is available at Q1 Emitter. When P2 is released, C1 starts charging slowly through R1 and when the voltage at its positive lead has reached about half the battery voltage, the IC gate outputs fall to zero, stopping Q1. This transistor can directly drive a portable radio receiver or different devices drawing a current up to about 250mA. Connecting a Relay across the Emitter of Q1 and negative ground, devices requiring much higher voltage and current operation can be driven through its contacts. Pushing on P2 for 1 to 5 seconds, the circuit starts and then will switch off after about 35 minutes. This time delay can be varied by changing R1 and/or C1 values. P1 will stop the timer if required.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Water Level control and monitor with PIC12F675
    flashing-light-uses-triacs.html
    how to make remote control circuit from
    converter lhc600a 40v
    Amp RC
    automatic garden light controller system
    Laser torch schematic
    Multifunction appliance protection circuit diagram



    Top