Autosport Labs

I am planning on hooking up an analog input from the brake switch on my car, however that is a 12 volt signal. How do I properly hook this up?

If you hook it up to an analog input, it would read 0 volts when no brakes are applied and 5v when brakes are on. Voltage limiting circuitry in RaceCapture/Pro will clamp the input voltage to 5v, even if you apply 12v on the terminal block. Inputs are protected up to 40v.

Give it try and let us know what you find out!

Okay, I will give it a try. I was hoping that was the answer, but I wasn't sure if it would go into some type of protection mode or not.

I assume you'll get a "1" on the brakes if you hook up the 12 volt signal to the digital input, correct?

You can also connect it to the digital input. The digital input has a pull-up resistor; so the behavior is:

input disconnected: reads as "1"
input grounded: reads as "0"

It just depends on how the brake switch is designed. If it grounds the circuit in order to illuminate the tail lights, you can hook it up to the digital input.

If the brake switch provides +12v to the lights when the brakes are pressed, then in order to use the digital input, you would need a *pull down* resistor on the input so the input sees zero voltage when the brake switch is not on. This pull down should be about 180 ohms to override the internal pull up resistor.

Come to think of it, the brake switch is likely switching ground, so using the digital input might be the better option, and saves an analog input port.

My brake sensor switches to ground and that's how I've hooked it up - to a digital input.

My brake switch does indeed provide 12 volts, so I hooked it up to Analog2, and set the value to be 0v = 0% and 5v = 100%. Analog2 works great, but for some reason Analog1 also shows 100% when I pres the brakes. Analog1 is hooked up to TPS. I tried Analog3, Analog4 and Analog5 for the brake switch but I had the same result each time, Race Analyzer showed Analog1 as 100% when I applied the brakes.

I did a log but I don't have an SD card reader (I'll stop and get one on the way home) so I can't say what the hardware is logging. Hopefully this is just a problem with RaceAnalyzer.

Hm. I would try hooking it up to a digital input; use a 180 ohm pulldown resistor between the input and ground. If you need help with this, I can draw a diagram.

Hi Brent,

I would appreciate a diagram. Is a "pulldown" resistor a special type of resistor, or can I just got to RadioShack and get a 180 ohm resistor?

180 or close to it fine. Use a 1/2 watt resistor from Radio Shack.

Basically the pull down is wired between ground and the digital input. then, the brake sense line is connected to the input.

PS. You really want this:
https://www.facebook.com/photo.php?fbid ... 230&type=1

so you can see brake data like this(scroll down)
http://www.race-capture.com/events/lemo ... ur/summary

it's worth getting the $100 sensor

Oh yeah I have plans to get one of those with a combination brake proportioning valve...it's a big job though so that's for next year.

! What is that diagram for?

I'm not sure I follow where the resistor goes. I am a simple software guy, I need to be spoken to very slowly.

That sensor is cool, but I'd rather not add another potential point of failure to the brake system. Just an indicator as to whether or not I'm on the brakes or not is enough for me. I'm more of a weekend warrior as opposed to someone trying to squeeze every last fraction of a second out.

No need to explain the wiring. I just hooked up the brake switch to a digital input and it just worked. No brake is 0 and touching the brake pedal is 1. This will work great for what I need!

\o/

Excellent! Glad it worked for you.