Need a 12v 2 pulse (only) circuit

Thread Starter

TeePee

Joined Nov 29, 2020
12
I have a caravan that is stored some way away from home and it is fitted with a 12v burglar alarm. I bought a cheap mobile phone and wired one of the keys to a relay that is operated by a pulse created by a 555 timer when the 12v supply to the burglar alarm siren is triggered. This works well EXCEPT I've discovered the mobile phone sleeps after a few minutes of inactivity and needs a brief pulse to waken it then another longer pulse to cause the phone to dial. I would also like this sequence to happen only once rather than it sending me a stream of messages. I have some 555 timers and veroboard, resisters and capacitors and can use a soldering iron. Any suggestions much appreciated.
 

ericgibbs

Joined Jan 29, 2010
11,551
hi TO,
Welcome to AAC.
Using two 555;s you need two Mono-stables, first one creates a pulse. when it times out it triggers a second monostable.
Use a couple of diodes as an OR gate as the output.
Do you follow OK.?
E
Post your present circuit diagram
 

eetech00

Joined Jun 8, 2013
2,162
I have a caravan that is stored some way away from home and it is fitted with a 12v burglar alarm. I bought a cheap mobile phone and wired one of the keys to a relay that is operated by a pulse created by a 555 timer when the 12v supply to the burglar alarm siren is triggered. This works well EXCEPT I've discovered the mobile phone sleeps after a few minutes of inactivity and needs a brief pulse to waken it then another longer pulse to cause the phone to dial. I would also like this sequence to happen only once rather than it sending me a stream of messages. I have some 555 timers and veroboard, resisters and capacitors and can use a soldering iron. Any suggestions much appreciated.
Turn off the sleep function.
 

Thread Starter

TeePee

Joined Nov 29, 2020
12
Thanks for the circuit Eric, just the sort of thing I was looking for. I'll build it and get back to you in a couple of days. TeePee
Just got around to building it Eric but I need a bit of help. I didn't make it clear that the 12v supply comes from the triggered burglar alarm i.e. power switches on when alarm sounds, so I had a go at altering your circuit as per attached but I'm not sure I got it right. Also, is that a capacitor in the diagram that I placed the question mark against and if so what value please. Finally, what sort of interval will I get between the 2 pulses and can I increase it if necessary ?
Many thanks for your help. Tony
 

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ericgibbs

Joined Jan 29, 2010
11,551
hi TP,
What delay period do you want between pulse 1 and pulse 2.?

Also are you requiring pulse 1 to occur when the 12V is switched On by the burglar alarm.?
I assume once the alarm is activated, the 12V is not switched Off until you cancel the alarm.?

E
 

Thread Starter

TeePee

Joined Nov 29, 2020
12
hi TP,
What delay period do you want between pulse 1 and pulse 2.?

Also are you requiring pulse 1 to occur when the 12V is switched On by the burglar alarm.?
I assume once the alarm is activated, the 12V is not switched Off until you cancel the alarm.?

E
Thanks for the prompt response Eric. Delay period say 1 to 2 secs after the first pulse which wakes the phone and ensures the dial out pulse is not confused and yes I want it to start when the 12v is switched on by the triggered alarm. The alarm will normally run for about 10 minutes then reset itself. If it triggers again, I would like the pulse sequence to start again. Hope I've made it clear. Once again thanks. T
 

ericgibbs

Joined Jan 29, 2010
11,551
hi TP,
This image shows a modified left side mono trigger.
The V1 represents the alarm trigger voltage supply,

Mono 1 triggers when the 12V is applied.

Let me know how long a delay gap you want between Mono1 and Mono2.

E

Update:

I see your reply, ie: 1 to 2 secs.
Would a 3rd 555 Mono be OK in your budget.?
If Yes, I will post a revised circuit.
 

Attachments

Thread Starter

TeePee

Joined Nov 29, 2020
12
hi TP,
This image shows a modified left side mono trigger.
The V1 represents the alarm trigger voltage supply,

Mono 1 triggers when the 12V is applied.

Let me know how long a delay gap you want between Mono1 and Mono2.

E

Update:
I see your reply, ie: 1 to 2 secs.
Would a 3rd 555 Mono be OK in your budget.?
If Yes, I will post a revised circuit.
I think I can run to a 3rd 555 Eric, thanks for your time and effort.
Tony
 

ericgibbs

Joined Jan 29, 2010
11,551
hi TP,
If you could accept say multiples of 1 second between pulses, we could use a CD4017 IC.?
Simplify the circuit and cost.
E
 

Thread Starter

TeePee

Joined Nov 29, 2020
12
hi TP,
If you could accept say multiples of 1 second between pulses, we could use a CD4017 IC.?
Simplify the circuit and cost.
E
I'll go for that Eric. Looks like the CD4017 is only a couple of quid so if that makes it easier, fine.
A delay of a few secs between pulses would be OK, first pulse about 1 sec second about 2-3 secs.
T
 

ericgibbs

Joined Jan 29, 2010
11,551
hi TP,
Look at this option, the outputs from the 4017 are on at 1sec intervals, use diodes on the outputs to get the combination you need.

E

Update:
If you want the pulsing sequence to happen just once, add this transitor modification.
 

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Last edited:

Thread Starter

TeePee

Joined Nov 29, 2020
12
While I was waiting for delivery of the CD4017 Eric, I thought I would have a go at the 3 X 555 solution. I took your 2 pulse solution and repeated the second stage on a third 555. It doesn't behave quite as I expected. The first 2 stages produce the output you predicted but the third stage produces an immediate output which then switches off when the second stage triggers and switches on again when the second stage completes. What have I got wrong ? Incidently the software you use looks great, is it expensive ?3PulseCircuit.jpg
 
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