Handbrake bypass switch

I bought a Pioneer radio and wanted to bypass the brake detection circuit to watch DVD’s. The unit has a wire that needs to detect nothing on the wire when you turn the vehicle on, and then a connection to Ground (handbrake on) before enabling the DVD player.

On the internet you can find a circuit where they use a relay to bypass it. The circuit looks like this:

Relay handbrake bypass

 

It works as follows:

  1. When you turn on the vehicle, there is no power on the Blue (Amp/delayed power) wire, so the relay is not energised and the Green (handbrake detect) wire detects nothing (connected to the Normally Open pin of relay)
  2. A short while later, power is delivered to the blue wire, energising the relay (switching it on)  and now the Green wire detects ground.
  3. The Blue wire is now permanently powered (that is, until you switch the vehicle off), so the Green wire keeps on detecting Ground (handbrake connected)

This circuit works, but for me the relay solution looked too clumsy and wasted unnecessary power keeping the coil energised, so I made the same circuit with a transistor.

Transistor brake bypass

This circuit works basically the same:

  1. When you turn on the vehicle, there is no power on the Blue (Amp/delayed power) wire, so the transistor is turned off and the Green (handbrake detect) wire detects nothing
  2.  A short while later, power is delivered to the blue wire, switching the transistor on,  and now the Green wire is connected to  ground.
  3. The Blue wire is now permanently powered, so the Green wire stays connected to ground (handbrake connected)

The transistor circuit is much smaller than the relay circuit and consumes  almost no current!

 

6 thoughts on “Handbrake bypass switch”

  1. would this work for the pioneer avh1450 dvd ? doesn’t the radio look for pulses in the handbrake circuit ?

  2. This circuit only switches on after it detects power on the blue wire, thus it looks like a pulse to the radio. (as if the hand brake was lifted after the vehicle started). It should also work on the avh1450.

  3. I bought one of these that people make off of eBay. But on mine when you pass 12v over the blue wire and connect the black to ground it starts to put out 9v on the green. 🙁 I’m guessing mine is broken.

    1. That does not sound right. First make sure you’ve connected everything correctly, if it still does not work, it’s probably broken.

  4. This is exactly what I thought it would be but could you provided details on the 10k resistor and NPN Transistor?

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