Archive: Toggling with timeout

Discussion in 'The Completed Projects Collection' started by BladeSabre, Jul 29, 2006.

Thread Status:
Not open for further replies.
  1. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    I'm trying to design a circuit where a pulse on the input toggles the output, but if the output remains high for a certain time (e.g. 2 seconds) it will go low by itself. Low output remains low until another input pulse occurs. (Again I'm looking to use low-voltage ICs with a 3V power supply, if possible.)

    The best I've been able to come up with is something like this:

    input --> toggle stage -(final output)-> missing pulse detector --> feed back and combine with input

    It seems a missing pulse detector is done with a 555 timer; and the toggle stage could use the other 555 on a dual chip, which might save space. That's still a lot of components though, including an extra IC for the logic gate.

    I'm thinking it would probably be easier to do this with a microcontroller. But there might be a simple circuit that I've overlooked. (Perhaps there's a clever single-stage 555 setup that will do this.) Does anyone here know of one?
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  3. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    Thanks, but I already read that page. It helps fill out part of the design I posted, but I'm trying to replace that with something smaller, which I don't think this page covers. The first two circuits are basic missing pulse detectors, and the others only seem to detect the first missing pulse?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    I think if you look at the datasheet for a CD4047 one-shot, you will be able to get it to perform your function.
     
  5. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    I've been thinking about that very hard, and I'm afraid I can't see it. May I have a further clue?
     
  6. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
  7. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    OK, I re-read your question and perhaps you want the output to toggle unless there is a pause in the proceedings for more than 2 seconds, in which case you want the toggle to reset. A quick drawing of the good ol 4013 with the output also being diverted to a basic R/C time constant which triggers the Reset pin oughta do the trick.
    http://img.photobucket.com/albums/v474/pe9le9/timedtoggle.gif

    the 4000 CMOS series are supposed to work as low as 3volts, but thats right on the very edge of their specs. Component count is 4, plus you have a spare "D" flip flop to play with. I havn't worked out the values of C and R but use a low value Cap, and high value resistor then work on the finer details of the time constant. This is just outta my head, so I havn't tried it, but can't see why it wouldn't work.... btw, if size is an issue, all these bits are commonly available in SMD.
     
  8. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    Yes, that's what I meant =).

    I don't have the equipment for using SMD, so size is an issue in the large-scale sense. Also I'm trying to minimise the number of solder joints.

    Thanks! That looks possible. The usual story for me- I'm having quite a struggle finding the CD4013 in a small quantity for a reasonable price. There's one on eBay for £2.25 which I could buy grudgingly =(

    EDIT: Maplin have got the 4027 (JK flip-flop) which I think might be able to do the same thing. Not sure though...

    EDIT2: Yes, that should work. I think the equivalent circuit is obtained by removing the feedback loop from /Q, and tying J and K to power.
     
  9. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Yup, your onto it. Should be fine. Slightly larger chip (by 2 pins) but similar availability. I always carry some of each in my parts tray, along with the inverters, Nands, Nors etc etc etc.
    Updated circuit...
    http://img.photobucket.com/albums/v474/pe9le9/toggle2.gif

    The 4013 retails here at $1.00 NZ (I think thats 33p UK money....I assume there are 100p in a Pound nowadays...??).
    the 4027 is the same price. (less in quantity).
    There must be a hobbiest somewhere with em...
    Good Luck
     
  10. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    Yes, your diagram matches what I was thinking.

    I'm going to get a small number of 4027 from Maplin at 83p each (they don't stock the 4013). If/when I next want £30 of stuff from Farnell, I can obtain both ICs for less than 30p- but that is some time away yet. (The 4013/4027 look really useful for other things too.)

    Thanks for your help. Hopefully I'll be able to try this out soon and see how it behaves in practice.
     
  11. BladeSabre

    Thread Starter Senior Member

    Aug 11, 2005
    105
    0
    It's working great! Thank you very much!
     
  12. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    No Probs. Theres still the odd thing you can do without getting a PIC and programmer out.... ;)
     
Loading...
Thread Status:
Not open for further replies.