Holding circuit for pulse signals

Discussion in 'General Electronics Chat' started by hspalm, Jun 18, 2012.

  1. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Hello,
    I have an rf receiver module. It has a signal regeneration chip on it, with one data line per remote control button (rf signals not the issue).

    The receiver module has four outputs, D0-D3 + VT (valid transmission). When I press a button on the remote the VT pin goes high until i release the button, but the corresponding data pin just blinks (high 100ms each 500ms) from VT goes high (button press) until it goes low (button release). I want the data pin to act like the VT pin, constant high signal while button is pressed.

    I've attached timing diagram of how it is today. I considered a one-shot 555 timer to trigger on data pulse and re-trigger for each pulse. But then I could have a transmission delay of nearly half a second which is not good when I'm using the remote to fine tune a lid with a motor on the output. So I need to take advantage of the VT pin somehow.

    Only using two data pins, each will trigger a relay (motor will spin fw/bw). So if I could latch the relay on data pulse, then release it when VT goes low, would be perfect. I've tried to come up with a solution, and I know what kind of chip I want, but don't know what it's called.

    The chip I need has 2 or more data inputs and outputs. When one input is pulsed the corresponding output is latched. The chip will be powered by VT pin, so the latch is released upon button release.

    Thanks for reading my post :)
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    It can be done with four CD4011 quad NAND gate ICs, one per output (See attached which shows circuit for two outputs). Two of the gates are configured as a SR latch and the third gate is configured as an inverter. You need a DC voltage to power the gates (5V-15VDC).

    You may need a transistor buffer on the gate output if you want to drive a relay.

    Edit: The DC voltage power to the gates should be equal to the input pulse voltage from the receiver.

    Pulse Strecher.gif
     
    Last edited: Jun 18, 2012
  3. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Thank you! I am a little worried about using two ICs for this "simple" task. Is there some aspect of this solution you see that I don't? I got an idea. Will this attached circuit work as a latch?
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    What are you "worried" about? ;)

    Your circuit tries to act as a latch the circuit by having the DATA signal overpower the output drive of the CD4050. But when the DATA signal goes low it will again overpower the output (if it has sufficient drive capability) and pull the latch back low. To make that circuit work reliably you would need to add a diode at the input and a resistor in the feedback connection.

    A circuit with two chips could be done with one CD4043 quad latch and one CD4009 Hex Inverter.
     
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