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LED Dashboard Indicator, Part 1

Simple, cheap and effective

by Julian Edgar

Click on pics to view larger images

At a glance...

  • Neat and compact dashboard indicator light
  • High intensity LED
  • Auto dims at night
  • Can be used to show revs, temp or mixture strength
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Oftentimes you need an on-dash indicator. It might be a shiftlight (to show it’s time to change gears), it might be a warning that the gearbox temp is too high, or it might be a pilot light to show that the intercooler water spray is working. You want it as near to your line of sight as possible (well, not buried down on the lower part of the dash anyway), and to be bright and highly visible. But, at the same time, at night you don’t want it to overpower your vision. Plus, no one wants the indicator to just be a pilot light hanging from an ugly pair of wires stuck to the top of the dash.

So whaddya do? In this two part series we’ll show you how to build a high intensity LED indicator. It’s mounted in a neat, black nylon holder that comes complete with angle adjustment and a mounting pad. The holder also shades the LED, allowing it to be more easily seen in daytime. Connected to one of the Silicon Chip electronic kits that we’ve covered in AutoSpeed, it can be configured to light up at a certain rpm or road speed; or when a high engine, gearbox, diff or intake air temperature occurs; show when the air/fuel ratio is rich; or even act as an alarm flasher. Furthermore, a high intensity LED is used but because the LED automatically dims when the car lights are on, there’s no problem with being blinded at night. Finally, you can easily adjust the night brightness level to suit your requirements.

This week we’ll show you how to install the LED in the mount and then locate it on the dashboard or A pillar, then next week we’ll cover the wiring that lets you run the LED from 12V and automatically dims it at night. All the wiring is straightforward and the whole lot will cost only about AUD$10-15 max per indicator.

The Mount

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The LED mount starts life as a nylon animal repeller. WTF?! Here in Australia these are designed to be mounted on the front of the car. As the car moves forward, air is forced through the front of the repeller and a high pitched sound is (supposedly) emitted. This (apparently) scares animals out of the way of the oncoming car. Most often, they’re fitted where a car is often passing through kangaroo territory. Cost for a pair is just AUD$4.50.

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The animal scarer makes for an ideal LED mount. The size is right and the tapered back-end looks good. Furthermore, the cone-shaped opening allows the LED to be easily recessed, shading it from direct sunlight.

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But how do you get the LED (and its wiring) into the mount? Making it easier is the fact that the mount pulls apart. The front section has an entry hole and there’s an outlet hole on its lower part.

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Both the front hole....

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...and the bottom hole need to be drilled out (the latter to take the wiring, arrowed here). But what size holes do we make them?

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Before you can drill the holes, you need to have the LED. You have two major choices – 10mm or 5mm LEDs. We chose the 5mm design which is more widely available in a range of intensities and colours. Pick a high intensity LED in a colour that’s appropriate – warning lights are usually red, for example. In this application, where two indicator lights were being mounted (one for intercooler spray on and the other showing rich mixtures), green LEDs were used. Electronics stores like Jaycar Electronics have a wide range of LEDs available.

High intensity LEDs are a different breed to normal LEDs. Most use clear housings (for example, a high intensity green LED will look clear until it lights up green) and have a narrower beam angle than conventional LEDs. Importantly, the current and forward voltage specs also vary for high intensity LEDs, so get these two specs when you’re buying. (More on this next week.)

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Drill out the front hole, using a drill bit just a little larger than the LED. You need to be able to fit the whole LED through the hole, rear flange and all. It’s easiest to hold the drill in a vice and rotate the nylon collar over it by hand.

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After you’ve done the front hole, do the bottom hole with a larger drill bit. Don’t go right through to the other side – just open to its full diameter the hole that’s already in one wall of the collar.

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Carefully bend the LED leads until they’re at right-angles to the LED. Don’t bend them right up against the LED as they’ll easily break off. Instead, bend them a millimetre or so away from the LED body.

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You should then be able to insert the LED in through the bottom hole, leads projecting out through this hole and LED projecting through the front, recessed hole.

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Very carefully fill the bottom hole with black silicone. Make sure the LED leads remain apart (otherwise they’ll short out) and push the silicone in so that it fills the hole to its full depth. Centre the LED in its hole and then put the assembly aside until the silicone sets.

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Cut the leads off short and then solder some light gauge figure-8 hook-up wire to them. Before you do the soldering, push some short lengths of heat shrink over the wires so that this will be able to be pulled back over the soldered joins. At this stage you don’t need to worry about polarity or a dropping resistor.

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Then use larger diameter heat shrink to make a neat assembly, with just the one cable going to the indicator light.

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Drill a hole through the mount for the cable and you’re done! If you prefer, the ‘aerodynamic’ trailing cone shape can be cut off short.

Now it’s time to take it out to the car and figure on where you’re going to mount it. Next week we’ll cover how to electrically drive it and also configure the LED so it automatically dims at night.

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