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Thread: HELP 2 flashing led circuit

  1. #1 HELP 2 flashing led circuit 
    Forum Professor captaincaveman's Avatar
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    Jul 2006
    help, hi guys looking for a circuit that will alternate two led's and be controllable to set the flash rate, also to be able to be switched with a ldr or equivalent. Also to run off one or two(paralleled) pp3 batterys.

    How long would a circuit be able to last of two pp3's in parallel? looking for as long as possible

    what i'm trying to do is set up a dummy alarm box, got the box, which is slim line with a blue plastic bottom for strobe, but normal mains alarms have two alternate led's flashing when in operation

    any help would be appreciated

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  3. #2  
    You are looking for a circuit called an 'Astable Multivibrator' the length of life will depend on the current draw by the LED's.

    If you want alternate flashing then the battery will last about 10 hours for every 100-maH the battery is rated (Nicad rechargeables will give about 12 hours).

    One of the resistors in the base of one of the transistors will need to be split into two series parts (1 part a constanct resistance, the other a variable resistence). THe LED(s) should be inserted in circuit between the collector of each transistor and it's load resistor.

    Off to the public library, send me the details of the componant values and I will tell you what to change them to.

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