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  1. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi George, I've been busy with other things the last few days - like doing my share of the housework instead of playing around with pieces of wire and resistors! Here's a link to a site that seems to have a different take on how a timer might be constructed...
  2. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Ah! I see, I'll have another go at the circuit - it's my novice status showing me up here! Thanks for your patience.
  3. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Fleck and I trust you are well. I've studied your posts and simulated your circuit as best I can (see below). The closest I can get to a 4020 in the Circuit Wizard simulator is the 4024 which is, I think, pretty similar to the 4020 except it's a 7-stage counter; and even then the Circuit...
  4. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Guys! great job on the circuit and it's going to take me a day to work through all your posts! I'll assemble a circuit that, hopefully, will reproduce your work using component values as close as I can get to your spec on circuit wizard. I'd be so excited to see how this goes.
  5. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Really sorry to have mislead you there guys!! Oooops! - all embarrassed now! :rolleyes: - I hadn't realised I'd confused things by mentioning the lamp - don't know what I was thinking at the time! I hope you're okay with the description I've given about a room heater needing to switch itself...
  6. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Just to be clear about what I want to achieve: A room heater (a simple resistive load of ~3kW) needs to switch on for a period of approx 1 hour and then switch itself off and stay off until the next time I give it a signal current to turn on again. Because this room heater is at my office 13...
  7. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Okay, I'll see if I can piece this new info together but I'd need one of your magic circuits diagrams :confused: if poss please? and I hope I haven't confused things by not giving a simple explanation of what I need to be able to do.....
  8. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Good morning George! I trust you're feeling better? Yes, the manual switch causes the relay to be switched off - obviously this shows that if the 4020 sends Q14 high enough they will switch off the relay as intended. This bit, though, doesnt happen. I've tried various outputs from the 4020 -...
  9. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    I've searched youtube and found this link that seems to do the sort of thing I'm looking for. this looks a bit beyond me at the moment!
  10. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Ah! yes, it does, when I bridge the 12V rail and the base of the 557's. I guess that extra volt (12..22 - 11.34) is sufficient to turn off the 557's?
  11. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Fleck, sorry for the delay in getting back to you. With LED's and 150Ώ to several outputs including Q14 (which is the one I've connected to the the 557's) All of them start flashing as soon as I apply power to the 12V rail. As suggested, I've removed the 1k's from the bases of the 557's and...
  12. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Fleck, thanks for letting me know how to use output 1 to show that the 4020 is counting. With reference to the BC547, it's there because, without it, the relay didn't seem to have enough power to operate so, I appreciate that this is overkill but please bear with me on this one until I get to...
  13. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    I'll check this out too soon, but first I want to get this 4020 working if poss.
  14. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Ah!, okay, I notice your earlier wiring diagram for the 555 shows pin 7 connected to the 12V rail via a 4.55M resistor. I would've followed that had it not been for Fleck's diagram that shows it to be unconnected (as is pin 5 on his diagram too).
  15. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Thanks for the amendments and, as you can see from the diagram below, I've put the relay back in for the time being (I like to hear something go click, I think!). As for the circuit, Fleck, you were right the 557 had blown and, since applying your suggestions, that part of the circuit works but...
  16. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi George, please join in - ideas welcome and I had no idea as to the low current transistors can respond to! there is a remote possibility that this circuit might just be working! I've assembled it as per the diagram below and I'm testing it right now, waiting for the 4020 to turn off the diode...
  17. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Fleck, thanks for that and I have gone ahead and built your design and rechecked all the connections. Before you suggested the extra 1k resistor, I got the 555's LED flashing happily away but there didn't seem to be a whole heap happening with the relay (it didn't switch on) until, that is, I...
  18. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Thanks Fleck, does that mean there'll be a total of 2K ohms between the two PNP transistors, with the connection with Q14 coming between the two 1k resisitors?
  19. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Ah! Following on from what I've just said I've re-read Fleck's earlier comment: - "When output 14 goes high it switches off both transistors, which disconnects the clock pulses and switches off the relay coil" So that might answer my own question even though I don't understand the properties of...
  20. Tim Metford

    Timer circuit that can ignore a persistent trigger current.

    Hi Fleck, I’ve been trying to work out how your diagram is supposed to work – I’m sure it’s my lack of electronics knowledge that's the problem so I’d really appreciate your help here! Puzzles 1. Your diagram shows both PNP transistors connected together via their bases (with a 1k resistor in...