Timer circuit that can ignore a persistent trigger current.
- Thread starter Tim Metford
- Start date
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 - their LED's all flash together but never achieve any sequence - i.e. they don't come on when it's supposed to be their turn, so to speak.
I've tried a new 4020 but the same result.
I cannot rule out the possibility of poor circuit connections though I've been over it several times and I pretty sure I've got it right (i.e. as per the diagram).
So, now that I've taken a look at a you tube video that shows a circuit doing what I want but uses some 4093's as well as the 4020, it may be that I shall need to get a little more sophisticated in the circuit and components used?
However, I can see the logic in Flecks diagram and I really like its simplicity - it'd be a pity to lose that by making a more sophisticated circuit!
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 - their LED's all flash together but never achieve any sequence - i.e. they don't come on when it's supposed to be their turn, so to speak.
I've tried a new 4020 but the same result.
I cannot rule out the possibility of poor circuit connections though I've been over it several times and I pretty sure I've got it right (i.e. as per the diagram).
So, now that I've taken a look at a you tube video that shows a circuit doing what I want but uses some 4093's as well as the 4020, it may be that I shall need to get a little more sophisticated in the circuit and components used?
However, I can see the logic in Flecks diagram and I really like its simplicity - it'd be a pity to lose that by making a more sophisticated circuit!
Hold on a minute lads, I've got a great idea. 
Use the 'normally closed' contact on the relay, then use an NPN transistor (bc547c) to energize the relay switching off the lamp.
Use the 'normally closed' contact on the relay, then use an NPN transistor (bc547c) to energize the relay switching off the lamp.
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 miles away I use an old mobile phone located in my office that I've adapted to send the current from its vibrator (when it rings), to activate a small relay that, in turn, connects a 12v dc circuit that then, in turn, powers on a 30A mains-rated power relay which supplies the room heater. This much is all up and working.
- However ......
- The timer circuit you've been helping me with is needed so that the heater turns itself off after about 1 hour.
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You turn on the heater by phone and just need a timer circuit to cut the 12v to the relay coil after one hour.
Have the 12v feed to the relay coil go through either a transistor or another relay with NC contacts to energize the timing circuit. After the time runs down the relay or base of the transistor is energized for just a second to cut interrupt power. Now it is back to its normal state waiting for you to call it on again.
I don't know if that is written so it can be understood LOL. I will draw something up tonight at work.
Have the 12v feed to the relay coil go through either a transistor or another relay with NC contacts to energize the timing circuit. After the time runs down the relay or base of the transistor is energized for just a second to cut interrupt power. Now it is back to its normal state waiting for you to call it on again.
I don't know if that is written so it can be understood LOL. I will draw something up tonight at work.
Really sorry to have mislead you there guys!! Oooops! - all embarrassed now! - 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 off and stay off etc,?
I like your idea, George about
I'll need to play around with how it might work and I look forward to seeing how my attempt compares with your's and Fleck's diagram when you're able to do them.
Thanks.
- 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 off and stay off etc,?
I like your idea, George about
I'll need to play around with how it might work and I look forward to seeing how my attempt compares with your's and Fleck's diagram when you're able to do them.
Thanks.
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