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Pulse circuit

Discussion in 'General Electronics Discussion' started by Pedro, Jan 17, 2015.

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  1. Pedro

    Pedro

    2
    0
    Jan 17, 2015
    I have built a time-lapse circuit for a camera, the output of which is a pulse (to take a picture) which can be repeated from seconds to days depending on the setting.
    The problem that I have is that on the longer time-lapse settings,the pulse gets wider and turns my camera off rather than take a picture.
    I need a circuit to take these pulses and outputs a short (narrow) pulse regardless of the length of pulse on the input.
    I would be grateful for some ideas!
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    Sounds like you need a type of mono-stable circuit. This can be easily made using logic gates and some timing components. Do you know what the minimum pulse is for triggering the camera? Also is the pulse active high or active low.
    Adam
     
  3. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    This might work. You may need to adjust the capacitor and or resistor values if the timings are not quite right. The voltage you use for the HEF40106 should match the output level of your controller. The capacitors for the supply of the HEF40106 should have a rating that is greater than the supply.

    If you choose ceramic capacitors then you shouldn't go much higher than the supply voltage. So if your supply is say 12 Volts go for the next value which would be 16 Volts. But if it's electrolytics or Tantalum then it doesn't matter.

    The circuit works like this, when a pulse appears on the left hand side of say the active high input capacitor C1 this high appears almost instantly on the other side. This high pulse triggers the Schmitt trigger inverter gate U1-1 and it's output goes low.

    This then feeds one of the outputs but also goes to another gate U1-2. This gate then goes high giving you a high output option. The resistor R2 discharges the capacitor C1 which when its voltage reaches the low level input threshold of the gate, the gate changes state and switches high.

    This then causes the other gate U1-2 to also change state and go low. The diode SD1 protects the gate of U1-1 from too high a negative voltage which happens when the input change back to its original state.

    The second circuit does pretty much the same thing but for active low inputs.

    Adam

    Camera trigger.PNG
     
    Pedro likes this.
  4. Pedro

    Pedro

    2
    0
    Jan 17, 2015
    Thankyou for your reply - it's very much appreciated.
    I'll breadboard a circuit and see what I can do.
     
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