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Conrad Car Reversing System - how to it an ultrasonic car reverse aid

Updated in 2013

Testing the Conrad Car Reversing Aid - a useful aid to help with parking or a gimmick? How easy is it to fit? Our step by step guide shows you what's involved.

As modern cars become ever more sophisticated, one after-market accessory that is becoming more popular is a car reversing sensor.

They employ several ultrasonic transducers in the rear bumper (fender) to measure the echo reflected from obstacles when reversing. An audio or visual signal warns the driver of a possible obstruction behind, and although a car reversing aid is not 100% foolproof they generally improve safety and confidence all round.

If you’re a physically mobile driver who's in good health, with good eyesight and a good sense of judgment then you might wonder why you’d ever need such a device. Many vehicles have awkward rear visibility, or a driver might suffer problems such as neck or back injuries that limit their ability to look over their shoulder when reversing. Also if, like the writer, you wear varifocal glasses then having a perfect panoramic view when maneouvering can be almost impossible. Even with perfect eyesight, if the car’s rear window is quite high up then you might not spot some obstructions, or a child or pedestrian might wander into your path without you noticing.

Since the cost of even a minor bump can be substantial (exploited by British car insurance industry "courtesy car" hire scams), a car reversing sensor can be a worthwhile  investment, or it can give you extra confidence when reversing.

This special EPEmag.Net article offers a total walkthrough with photos, showing what’s involved when installing a good-quality ultrasonic car reversing system into a typical saloon car – in this case, the writer's Honda Civic, a car that’s seldom easy to ‘place’ accurately and is even worse to reverse!

A number of after-market car reversing systems are on sale that vary from very basic bleeper systems to more sophisticated ones with digital displays, or even small camera systems that fit to the rear licence plate. I liked the looks of the Conrad "Parking System" (Einparksystem) from the German mail-order supplier Conrad Electronics, a Maplin-like distributor who claim to be Europe’s largest supplier of their kind. Conrad advertises occasionally and has a comprehensive website. They deliver worldwide.

The colourful and informative animated dashboard display uses a vacuum-fluorescent display (VFD) - but it's much less legible in bright light. The tube is very cluttered with non-illuminated electrodes though. A clear audio signal is also emitted which can be switched off.

Conrad’s Parking System is a PIC microcontroller-based system (the circuit diagram is included!) which operates four waterproof ultrasonic sensors, but the main attraction for the writer was the multicolour vacuum-fluorescent display (VFD) that fits to the dashboard. The VFD provides a digital readout of distance measurement in 10 cm increments (starting from up to 2 metres away depending on conditions), and a colourful animated ‘radar' display of the car, to show the proximity of an obstruction (in metres only) and whether it’s on the left or the right (or both).

Kit Contents

  • Multi colour animated vacuum-fluorescent display (VFD) with mounting bracket
  • Control box
  • 4 x ultrasonic sensors with wedge-shaped rubber seals
  • Signal and power cables
  • 21.5mm HSS cutter
  • 2 x Scotchlok-type connectors
  • Multilingual instructions

The dashboard VFD is a small black display unit measuring 66 x 56mm with a shiny glass window. It's fitted with a basic L-shaped metal mounting bracket. A tiny 3-position switch on the rear offers Off, "V" mode - sound and display, or "M" - display only modes. Power comes from the reversing lights, so the unit only operates when you select reverse gear. It draws about 100mA maximum.

The control unit is a small moulded box for mounting in the boot (trunk). The four ultrasonic sensors themselves are sealed plastic units that are push-fitted into the rear bumper. They have generous cable lengths (too much for my Honda Civic!) that would accommodate the largest car, MPV or 4x4. A generously long cable with miniature multiway plugs at each end interconnects the control unit in the boot and the VFD display unit on the dash.

Initial survey - careful planning is the key to success

Planning is absolutely essential or you risk causing unsightly damage to your car. First we’ll look at the initial (and essential!) survey your car needs before fitting any such car reversing alarm. The biggest consideration must be the rear bumper of your vehicle. All modern cars have plastic bumpers but directly behind them there'll usually be a steel beam for collision protection. The only way to know is to take a look underneath.

Check carefully the clearance behind the plastic bumper, to ensure that bodywork or steel bumper (represented by the red dotted line) will not foul the sensors. The top couple of inches just above the steel bumper (green dotted line) were clear on this car, so that's where the transducers had to go.

In my own car, a steel beam lurks close behind the curved plastic bumper, but (most importantly) a gap exists directly above the beam that allows space for the four sensors to be inserted along the top of the bumper. It’s critical to check and get this right, because it would be disastrous to drill the bumper only to find there was no clearance behind to accommodate the sensors.

Another consideration is to make certain that no wiring, fuel lines, etc. would interfere or be damaged by drilling. Hence I spent quite some time checking out the car’s layout to ensure the sensors could be fitted without a problem.

Next, how to route the four cables into the car: I struck lucky with the Civic because two large plastic plugs (possibly for a towbar) were fitted into the spare wheel well at the rear, which would allow the cables sensor cables to run directly into the boot. Otherwise, you’d have to think about drilling a hole into the steel chassis, preferably on a sheltered trailing surface that won’t be directly affected by rainwater. (A grommet would be compulsory to prevent damage.)

Spare wheel removed - note the removable long black polystyrene packing piece A bung in the spare wheel well would form the ideal cable entry for the four transducers
The car has two expanded polystrene blocks that support the removable floor, which would be a suitable home for the control box underneath,

The third aspect is the siting of the control box in the boot or trunk area. The small lightweight unit can be screwed or stuck down with an adhesive pad (supplied) preferably where it will be shielded from damage. Consider fitting it inside the rear wing somewhere, behind the boot's plastic liners or near a rear light unit. In my case, the boot has large expanded polystyrene blocks under the floor, either side of the spare wheel which would be a perfect place to store the electronics. The main signal cable could then run through into the passenger compartment to the dashboard.

I decided to route it within the doorsill's plastic trim, and behind the driver’s side footwell trim and up into the dashboard.  I also found that the Honda’s dashboard has a removable end-panel that fitted impeccably, so I could run the cable up through the dashboard on the driver’s side.

At this point you might consider buying a Hayne’s Manual for your car (e.g. from Amazon, Halfords or eBay) which might save you a lot of grief should you need to dismantle and remove any trims. They aren’t really designed for removal: the plastic plugs can become brittle with age and they can break quite easily. It would be disappointing to damage any fittings in the process, but brute force should be avoided. (Trim removal tools are available from eBay.)

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