Leading & Lagging edge pulse generator

Discussion in 'The Projects Forum' started by zirillo, Mar 24, 2014.

  1. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    Would like to use a 24 hour on/off timer to generate a 1 or 2 second pulse to operate a remote control device. The timer is off for daylight hours and on for sunset hours. Would like a circuit to generate a 1 to 2 second pulse whenever the timer changes state. It seems that a circuit that generated a pulse for leading edge and trailing edge is required. Any ideas?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Missing a few details.

    What is the remote device and what are its control requirements? Voltage, current, open-collector, AC relay contacts - what?

    What is the power source for the timer and for the device? AC, DC, battery, etc.

    This can be pretty simple if the details are in your favor. I'm sure there are industrial cycle timers that will do this ($$$), but there are other ways. If all you need is a 5V pulse, for example:

    Cheapo lamp timer from WalMart gets you the on/off cycle. Plug in a universal cell phone charger, the kind with a mini-USB connector. This gets you +5VDC, all UL rated and short-curcuit protected. Next comes a simple circuit that generates the 1-second pulse at turn-on and turn-off. The circuit would have to have a small hold-up capacitor to power the pulse circuit after the DC supply is turned off by the timer.

    ak
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,148
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    Of what? Something like 12v DC?

    Oops, AK beat me to it.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Thought about the circuit. Depending on your requirements, it might fit in one 16-pin device, and run on anything from 5 to 24 VDC.

    ak
     
  5. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    1. The remote device is a hand held transmitter that requires a pulse to trigger. Will use the pulse to control a small 12 volt relay.
    2. The power source is 120 VAC. Its a photoelectric device that will be used to control lights at 3 remote locations I will use a power supply to use this to drive the pulse circuit.
    3. Only need the pulse, will design other circuits. You mentioned capacitor holding the charge at times the cycle might be around 12 hours long. Is there a circuit for this? Will be will to try it out.

    Thanks for the help.

    There is a commercial X-10 system available but is time dependent and not photoelectric.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Again, a pulse of what?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    A pulse up to 15V (equal to its supply voltage) can be easily generated by a CD4070 XOR gate. Connect the voltage that changes state directly to one input and through an RC delay (series R with C to ground) to the other input. This will generate a pulse on both the rising and falling edges of the input with a pulse-width of about 0.7*R*C (for example R= 200k and C= 10μF for a pulse width of ≈1.4s).
     
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  8. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    Around 12 VDC for1 or 2 secs. Enough to drive a small relay
     
  9. crutschow

    Expert

    Mar 14, 2008
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    You would likely need to add a transistor (e.g. 2N2222) driver to the XOR output to drive the relay. What is the relay coil resistance?
     
  10. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    Coil R= 600 Ohms
     
  11. crutschow

    Expert

    Mar 14, 2008
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    So you do need a buffer amp.

    You could use a 2N2222 or comparable transistor. Connect the emitter to ground, the base to a 10k resistor, and the collector to one of the relay coil connections. Connect the other end of the base resistor to the XOR output and the other side of the relay coil to +12V. Connect a diode (1N4148 or comparable) across the relay coil (cathode to +12V side) for spike suppression.
     
  12. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    Thank you for your help, had to order the CD4070BE from Digikey. This will take a few days. Will have to order an astronomical timer to drive a 120vac power supply to supply low level input (5v thru 200k resistors) to the inputs of the 4070BE.
     
  13. crutschow

    Expert

    Mar 14, 2008
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    CMOS circuits require an input voltage equal to the supply voltage for the logic high. So do you have 5V to power the CD4070 and 12V to power the relay? Or else power the CD4070 with 12V and generate 12V for the input.
     
  14. zirillo

    Thread Starter New Member

    Mar 24, 2014
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    Did not know one could go as high as 12V for the logic input. Will use the same 12v supply for the input logic, relay drive and 2N2222.
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Playing around with a different approach, based on a logic circuit I did long ago for an ambulance company. The ULN2004 is an array of seven darlington transistors complete with base current limiting resistors and input pulldowns, 50V, 1/2A rating, and transient suppression diodes for driving things like...relays. With one chip, one SIP resistor network, and two timing caps get you all of the logic, relay drive, and an auxilliary output.

    Timer U1A makes a pluse when the lamp timer comes on. Timer U1EFG makes a pulse when the lamp timer turns off, powered by the two large holdup caps. U1B and D OR the two timer pulses into the relay coil.

    ak
     
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  16. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Looking at the schematic this morning, it hit me that I don't need a separate turn-off pulse generator because the relay coil discharging the holdup cap is a time constant. That eliminates three inverters. Hmmm...

    OK, Monte, I can name that circuit in one transistor (and two diodes). I hope Bucky is smiling.

    ak

    "Doing more with less." - R. Buckminster Fulller, architect, futurist, minimalist, namesake of the "Buckyball" carbon molecule
     
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  17. waran1

    New Member

    Apr 24, 2016
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    Hi,
    the pulser-2 circuit does not show where two inputs that comes from the timer device, please enlighten me, i need this circuit for slimier application.
     
  18. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    It's right on the schematic. A standard lamp timer plugs into a wall outlet, a standard small plug-in power supply (a wall wart) with a 12 V output plugs into the timer, and the 12 V output powers the circuit.

    Note that this circuit is not rated for *slime* applications.

    ak
     
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