alarm door opener help

[kedgenz]

hi im work in car audio and communications

im currently installing hand brake warning systems into a ford ranger but they dont have door switch's and can't install new ones as it voids the warrenty on the car.

i have sort of solved the problem by using the dome light wire but now when the voltage raises when the door is closed the buzzer will change pitch with the voltage increasing down the wire

its a negitive feed system and need a way to make a circuit so when the dome light wire only goes to .5V or lower it will switch a relay or transister anything above .5v the buzzer wont go off.

or

i used a relay to see if i could get it work the way i wanted but the trouble is as the voltage increase across the coil the relay makes a funny sound so can i use transisters instead of a relay

in a relay configuration i would put 12v on 86 and use the doom light to activate the coil on pin 85 and then use 30 on ground and 87a on the buzzer side so when the relay see's a ground from the dome light it will earth out turning on the buzzer

any help be great

 

[john monks]

Why not drive the relay with a transistor?
Seems like you could use a voltage follower so that the relay does not effect the cars circuitry.

 

[mechtronics]

yes as long as you have the right pins on the relay connected the right way, but it sounds to me like the relay isn't getting enough current through its coil in order to activate. i presume it is a kit you are wiring in with some kind of control box on it? i was thinking maybe you could use some kind of voltage divider off of the dome light, that feeds a transistor.?

have you got any wiring diagrams on the handbrake systems that you have so we could have a look at that will help

 

[kedgenz]

all ready asked distributer if i can get a diagram but dont have any

its 3 wires

12v
handbrake wire grounds when off
door grounds when open

we have transisters made up for the seatbelt so may try one of these with a relay
these transisters swap the - triger from the seat belt and turns it into a possitive

basicly when the handbrake is off and door is open with a switch you get ground, and buzzer goes off constant and no delay. as i have it wired on the doom the wire is 12v with door closed and when you open the door the dome light fades on and the 12v drops to ground slowly making the buzzer sweep as the voltage goes down

so i only want the buzzer to see ground nothing else

 

[kedgenz]

in regards to the relay it does work but you can here the relay buzz befor it clicks so just need the relay to see a ground and nothing else so hoping a transister should be able to turn on when it gets a ground will try it in the morning

 

[mechtronics]

you could maybe use an inverter too to get over the relay problem that you are having

 

[CDRIVE]

handbrake wire grounds when off
door grounds when open

This circuit it based on the quoted statement.

 

[CDRIVE]

It just occurred to me that you probably won't need the relay any longer. Here's the same circuit with direct drive to the buzzer.