It was after I nearly ran over an old woman that I thought I’d better make the modification.

Posted on October 10th, 2004 in Opinion by Julian Edgar

It was after I nearly ran over an old woman that I thought I’d better make the modification.

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My Japanese-import ’99 Toyota Prius – a hybrid electric/petrol vehicle – has no reverse gear in the gearbox. What happens is that the electric motor alone is used to propel the car backwards.  In fact, if the petrol engine is up to temp, it switches off whenever reverse is selected.

The incident happened after I’d just jumped into the car – parked outside the local post office – and started the engine. The petrol engine came to life (though without any whirr-whirr of a starter motor as the ‘starter’ is always engaged) but then immediately switched off as I put the gear lever into reverse.

An elderly woman had been trying to cross the road behind me. She’d paused as the engine had started, but then as soon as it stopped, stepped straight into the path of the reversing, silent, Prius. She was watching the road for traffic coming up behind the Prius and so was completely unaware of the car moving towards her.

It was just by chance that I glanced in the central rear vision mirror and saw her figure directly behind the car. I braked hard, the car stopped, and she crossed the road after an approaching car had passed – completely unaware that she’d nearly been reversed over.

I am not usually one for reversing beepers in cars, but the Prius is a car that really needs it.

So when I came across an electronic module that would allow me to easily implement a beeper, it was only a 30-minute job to install a reversing warning.

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The electronic module is a beauty – a Brodersen XM series Unic timer. I picked up two of them at the shop at the local rubbish tip – along with about 30 plug-in relays and all the bases, they were still in place in a discarded mains power industrial switchboard. I bought them because they looked interesting and at $5 for the timers and all the relays, there wasn’t much to lose.

However, it wasn’t until I got the timers home and looked at them closely that I realised what little beauties they are. Incredibly, they are able to operate at any voltage from 10.5 to 265 volts, AC or DC! That makes them as suitable for use in cars as it does in mains-powered switchboards.

There are front controls for a power-on delay, power-on pulse, recycling pulse, and recycling pause. Another pair of knobs allows adjustment of the timing from 0.6 seconds to 60 minutes. The module has an in-built double pole, double throw (DPDT) relay and plugs into an 11-pin octal socket. Making things even easier, a wiring diagram on the side shows all the connections. (You can download the datasheets for the full range of these electronic timers at

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Powering the module directly from the reversing lights and using the in-built relay to trigger a variable volume buzzer (I used one of these – AutoSpeed Shop) resulted in a suitable system. Initially, I set the timer to give a 5 second warning whenever reverse was first selected but then I decided a traditional beep-beep-beep was much more attention-getting. I mounted the timer module (green arrow) partly inside a boot panel and the buzzer (red arrow) was located near to the cabin ventilation outlets.

(Incidentally, the Auto Timer kit – that will be available later this year from Jaycar Electronics – will be able to perform a similar function to the Brodersen timer.)

Now I don’t expect reversing beepers to suddenly sweep the modified car fashion world, but in some cars they’re a necessity. And anyway, keep an eye out for those Brodersen timers – there’re lots of uses for those in all sorts of modified cars!

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