Wiring in a monostable 555 timer trigger to a car ignition

J

James

New Member
#1
#1
I have made a monostable 555 timer circuit that will light a 12v LED for about 5 seconds and then turn off.

The only problem is I don't have a trigger. I want the circuit to activate when I get 12V on one of my ignition wires. Is there a simple way to do this?

Thanks any thoughts are greatly appreciated!
 
F

Fleck

Member
#3
#3
Ive never made a monostable but I think you're on the right track with a transistor.

Try this: connect a 10k resistor between pin 2 and the supply, then connect a BC547c transistor collector to pin 2 with the emitter going to ground. Base goes to 12v ignition via another 10k resistor.

The only thing is the trigger pulse stays on so I don't know if that will make the output perminantly on. Try it anyway.


Rich
 
J

James

New Member
#4
#4
I managed to get a relay from Maplin. It temporarily touches when the ignition is turned on, effectively acting as a push button switch. Works :)
 
R

ryanh1008

New Member
#5
#5
James said:
I managed to get a relay from Maplin. It temporarily touches when the ignition is turned on, effectively acting as a push button switch. Works :)
Click to expand...
This sounds like what I'm looking for. When I unlock my car I want the rear lights and head lights to come on. I will have a 12 supply and the trigger will be taken from the central locking so when I unlock the car it will be high for a second and then go low. I'm wanting my lights to stay on for around 10 sec, have you just used the basic monostable circuit?
 
D

DeanK

New Member
#6
#6
I am very interested in the circuit as I am building a "Custom" Body Control Module for my 67 C10 truck. What details can you supply regarding the realy from Maplin? I am using an aftermarket keyless remote with a simple "On" or "Off" state. To keep parasitic drain low, I want the keyless relay to be the only drain that tested at 0.040mA thru the coil when on. Total functions, Lock, Un-lock control, Theft with ground input triggers, Light control - blink when locked & un-locked using MOSFETs (Diodes on each circuit) and 555 timer. I am considering an active 5Vdc regulator to drive sheilded LED to LDR to allow different modules to remain off until needed. Retired ASE Master Tech with strong electrcial diagnostics skills, but this is first time building electronics. Any suggestions welcome. Thanks!
 
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