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transistors motorcycle alarm.


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hellonwheelz 
Member - Posts: 2
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Joined: September 16, 2014
Location: New York, United States
Posted: September 16, 2014 at 2:51 PM / IP Logged  
I have a gps103a that has + and - door trigger inputs.
I'd like to use transistors to have a "wire cut" trigger on the neg door input.
I'm putting a big loop of continous wire on the motorcycle cover and I want my alarm to go off if the circuit is broken.
I don't want to use relays, because I need to keep the power consumption to the bare minimums. MC battery is very short on juice, and the GSM and GPS alarm are already pushing it.
Thanks 12v!
oldspark 
Gold - Posts: 4,913
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Joined: November 03, 2008
Location: Australia
Posted: September 16, 2014 at 6:33 PM / IP Logged  
Any FET or MOSFET or transistor inverter circuit.
The grounded or +12V connected loop keeps the transistor off; when the loop breaks a pull-up or -pull-down resistor (to the opposite ie, +12V or GND rail) turns on the transistor, or vice versa if desired (door inputs are usually a -ve going or GND trigger, nit a wire cut).
Make it DC sensing (a low pass filter) to prevent RFI triggering.
Ween 
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Joined: August 01, 2004
Location: Illinois, United States
Posted: September 16, 2014 at 6:58 PM / IP Logged  
Or a DEI 502T for the less glamorous solution.
hellonwheelz 
Member - Posts: 2
Member spacespace
Joined: September 16, 2014
Location: New York, United States
Posted: September 17, 2014 at 3:49 PM / IP Logged  
Oldspark thank you, do you have an example circuit i can wire up?
Sorry for asking to be spoon fed.
KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: September 17, 2014 at 4:12 PM / IP Logged  
Is the transistor even necessary? Use a high value resistor (>10K ohms) to tie your (-) door input to ground. Then, connect your loop through (+) voltage. You may want to add a 10K ohm resistor in line with the (+) feed as a current limiter but you may need to play with the values to get them to work together and trigger properly.
Kevin Pierson
i am an idiot 
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Joined: September 21, 2006
Location: Louisiana, United States
Posted: September 17, 2014 at 8:41 PM / IP Logged  
x2
Ween 
Platinum - Posts: 1,364
Platinum spacespace
Joined: August 01, 2004
Location: Illinois, United States
Posted: September 17, 2014 at 9:56 PM / IP Logged  
I think you want to use the pull-up resistor on the (+) trigger input.
The wire loop is used to connect this input to ground. Cut the loop, +12 volt flows through resistor triggering input, not to ground. Your standby current draw is the battery voltage divided by pull-up resistor value...ohms law.

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