Quick Brake!

Ever been punted up the arse? OK, OK, we’re not talking about your sexual proclivities but instead about the rear of your car. Ever been subjected to a big rear-end impact – y’know, you’ve been braking but the guy behind wasn’t? Not much fun is it – they might always be classed as legally in the wrong but that doesn’t help you if they don’t have insurance... not to mention the hassle of having your car off the road, getting decent paint matching and all the rest.

But now we have a solution. Nope, not to take all the brain-deads off the road but instead to give them metres more time to react to the fact that you’re slowing down. You’ve heard how LED brake lights illuminate faster than filament lamps to give quicker warning? That certainly helps - but how about lighting the brake lights before you even hit the brake pedal? It’s possible to do this if instead of switching the brake lights on with the action of the brake pedal, you instead activate them when you first lift the throttle really fast.

It’s a technique unfortunately not suitable for manual transmission cars (cos the brake lights would light on every gear-change) but for auto trans cars it works beautifully.

But how does it work?

Delta Throttle Timer

The trick is to use an electronic module that’s always monitoring the voltage coming out of the throttle position sensor. When you lift the throttle really quickly – like you do just before stamping on the brake pedal in an emergency stop – the voltage out of the throttle position sensor falls rapidly. This trips a relay. The relay is wired in parallel with the normal brake light switch, so on come the brake lights. To keep them on in the short period when your foot is shifting from the throttle to the brake pedal, an inbuilt timer keeps the relay pulled-in.

The Delta Throttle Timer is the name of that tricky electronic module.

So where did it come from? The Delta Throttle Timer was developed and designed by www.siliconchip.com.au electronics magazine. It is one of a number of projects that will be covered in a unique Silicon Chip publication - High Performance Electronic Projects for Cars - which will be available from newsagents in Australiaand New Zealand, or online through the AutoSpeed shop. The book will be an absolute must-have for DIY modifiers.

The electronics design and development of the Delta Throttle Timer were carried out by the skilled and modest electronics engineer John Clarke, while I came up with the concept and did all the on-car development. (During this period I wore a different hat to an AutoSpeed contributor, working for Silicon Chip Publications as a freelance contributor.)

So while by no means should the Delta Throttle Timer be seen as an AutoSpeed-developed project, we’re very happy to endorse it.

The electronics kit for the Delta Throttle Timer is available from Jaycar.

The Module

If you have assembled other electronic projects before, the Delta Throttle Timer (or QuickBrake) kit shouldn’t cause you too much trouble. There are 18 resistors, 13 capacitors, 13 semi-conductors, assorted terminals, the relay and two trim-pots. Solder and hook-up wiring is supplied. Follow the instructions carefully – in fact to gain the article in full colour (important when following a component overlay) we suggest that you subscribe to the on-line version of the article at Increase your driving safety with Quick Brake.

However, if you’re not confident with component identification, component polarity and soldering, buy the fully built and tested version – then only a few simple connections to the car are required.

Neither version comes with a box, however the Delta Throttle Timer (we’ll call it DTT from now on!) fits straight into a 130 x 68 x 42mm plastic electronics ‘jiffy’ box. Alternatively, you can put it in any box that you want, making sure that the bottom of the printed circuit board can’t come into contact with anything metallic (which could cause shorts).

When you have either built the kit or received the built-up module, have a good look at it. Orientate it so that the relay is on the right. Now you’ll have two sets of terminals on the left and a long strip of six terminals on the right. The top-left terminal connects to ignition-switched 12V – that is, a battery positive supply that is on when the ignition is on. The terminal right below connects to ground – in other words, to the car’s metal body. The lower left terminal has two inputs but as they’re connected together, either one can be used. This input is for the wire that connects to the throttle position sensor.

Before you can connect the signal input to the throttle position sensor you need to find the right wire on the sensor. To do this you’ll need a multimeter. Set the multimeter to ‘Volts DC’ and connect the black lead to the car’s body. Turn on the ignition. With the other multimeter input, back-probe the working throttle position sensor until you find a wire that has a voltage on it that varies with throttle position. Typically, this will be in the 1-4V range and the voltage will rise when the throttle is opened. This is the wire that you tap into for the DTT signal.

Connect up these wires to the DTT. (Note that the throttle position signal wire doesn’t need to be cut – the DTT just taps into it).

Testing

Now that you’ve made these connections you can do some testing.

Turn Pot 1 (Sensitivity) anti-clockwise as far as it will go. (Note that these are multi-turn pots so you may not come up against a positive ‘stop’ when you get to the end of its rotation.) Turning the Sensitivity pot anti-clockwise increases sensitivity. Next turn Pot 2 (Time) clockwise to decrease the period that the timer will stay on. Finally, check that the moveable link is in its right-hand position, which causes the DTT to turn on with fast throttle lifts.

Switch on the ignition, wait for 10 seconds, push down and then quickly release the throttle. The LED should come on and the relay pull-in for a short time. (The 10 second delay after switch-on is needed because the DTT has a built-in pause to avoid false-alarming when power is first applied.) Then turn the Time pot anti-clockwise a little to extend the relay’s ‘on’ time. The range of adjustment is from 1/10^th of a second to just under 2 minutes - in this application, around a second is fine.

Adjust VR1 clockwise until the DTT responds only when the throttle is being lifted with ‘real life’ quick movements. If you find that you’re right up at the ‘most sensitive’ end of the pot’s range (ie fully anti-clockwise), you can either change VR1 to a pot of higher value (eg 2 meg-ohm) or increase the value of the 100 kilo-ohm resistor in series with VR1 (eg to 1 meg-ohm)- but you shouldn't have a problem in this area.

Fitting

When you have the DTT working as you want, it’s time to make the brake light connections. These are dead-easy. You’ll first have to locate the brake-light switch (it’s normally mounted way under the dash at the top of – wait for it – the brake pedal). There will be two wires that go to the switch – join a new wire to each of these. Make sure that you use a wire capable of handling at least a decent amount of current – IOTW, not just very thin hook-up wire. (The wire supplied with both the kit and fully built up DTTs is fine.)

When you join these two new wires together, the brake lights should come on. Now connect these wires to the adjacent ‘Normally Open’ and ‘Common’ connections on the DTT’s relay terminals. Turn on the ignition, wait the delay period of 5-10 seconds, push down on the throttle then rapidly lift your foot. The brake lights should come on before you even touch the brake pedal! Practice lifting your foot from the throttle at emergency speeds and putting it on the brake pedal, and set the timer so that this transitional period is just covered.

Conclusion

When you watch a car equipped with this brake-light trigger suddenly slowing, the speed with which the brake lights come in is almost uncanny. There’s certainly no doubting that following drivers get a far earlier warning that the car is stopping than with traditional systems.... and that can save your arse.