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LCD Temp Display!

Jaycar's new LCD temp display has a vast number of applications in a modified car. Here, we take your through just one of them...

By Michael Knowling

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A LCD temperature display can be a very useful instrument for your vehicle. You can measure:

  • airbox temperature
  • turbo outlet temperature
  • post intercooler temperature
  • ambient temperature
  • interior temperature
  • coolant temperature
  • engine and gearbox oil temperatures
  • amplifier temperature

In fact, the operating range of the unit and your imagination are the only things that limit you.

As a general guide, most $30-$60 LCD temp meters have a range from about -20 to 70 degrees C. However, with the release of Jaycar's new $39.95 module (cat number XC 0224), you can now read all the way from -50 degrees right up to 150 degrees Celsius. This far-reaching temperature range makes the unit truly ideal for those of us that are testing the intake air temps on a psi pushin' turbocar. Yep, it's just what we've all been waiting for...

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Amazingly, your $39.95 doesn't just buy you the bare LCD display - you also receive the necessary thermistor probe on the end of a metre length of wire. The accuracy of the matched display and probe is listed in the accompanying instruction/spec sheet as plus/minus 1 degree, over nearly the entire -50 - 150 degree C operating range. So that's probably about as good as most of us will ever need... Resolution is set to one tenth of a degree and the display is automatically updated every second.

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In addition to simply displaying temperature, the module also has a number of user-configurable features. The four small push buttons across the back of the main body allow you to program both high and low temperature alarms (which sound four times per minute while the preset temperature is exceeded), plus you can also bring up the minimum and maximum temperatures that have been measured. It's sort of like the peak recall function on a good aftermarket tacho. The whole shebang is powered by a 1.5V battery (which is accompanied by an on-screen low battery level indicator) and comes mountable with a large plastic sucker cup on the back (easily removed!).

So - with that dorky sucker cup now ripped out - how do you get the meter and probe into your car? Easy...

Installation

Certainly, one of the most common uses for the module will be to measure intake air temps on boosted turbocharged vehicles. Here's one example of an installation that we prepared earlier...

The first step is to work out where you want the display unit mounted and where you want to take the measurements. We decided to remove our VL Commodore's push-in blanking panel (just to the left of steering column) and locate the display in this void. Then - peering under the bonnet - a small metal blanking plate on the right hand underside of the intake plenum grabbed us as the best place for the sensor probe. We selected this as our probe location because the sample temperature would be a very close representation of the air passing into each inlet port and - very importantly - the blanking plate was easily removed and then replaced. It was bound to be a lot easier (and safer!) than later trying to drill and tap directly into the plenum chamber!

Now we get down to it...

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Fitment of the LCD display required initial checks to ensure there was enough clearance to slot the unit in without fouling anything. Everything looked sweet here, except we were inevitably going to have to put a hole in the plastic moulding that backed the push-in blanking panel. Knowing it would eventually all fit in, we then made up an all-new faceplate to house the display. Using a small sheet of black ABS plastic (complete with leather grain to match the rest of the car's plastic trim), we cut and filed a square section to fit into the dash cutout. That done, we marked out where the LCD display would be poking through this newborn faceplate.

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The offending area was removed by drilling a large pilot hole and working our way around our fascia outline with a mini hacksaw. The edges were then straightened and cleaned up with a file. With our new plastic faceplate now complete, the next step was to put a large hole through the moulded plastic panel that lay immediately behind it. This was done - again - with a drill, mini hacksaw and file. Finally, we pushed the display into the middle of the faceplate, stuck the assembly into its position in the dash and - voila - module mounted!

Now we move onto the task of installing the 45mm stainless steel sensor probe...

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Because we elected to mount the display in the cabin and the sensor probe under the bonnet, we were forced to extend the one metre length of connecting wire. But to check that we weren't about to mess up the display accuracy (by varying the resistance in the thermister circuit), we first tested its readings. This was done by inserting the probe into a mix of ice and water (zero degrees C) and then into boiling water (100 degrees C). The module's readings were then pitted against a digital thermometer in a shared glass of warm tap water. What was the reasoning behind all of this, you ask. Simple. This procedure gave us figures at low, medium and high temperatures - a wide spread of readings was what we were after.

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Now, with our baseline noted, we soldered in a 1.5 metre length of dual-core insulated hook-up wire - a size that gives us scope to relocate the sensor anywhere else further down the track. Immediately after, we again tested the accuracy of the display. Phew... much to our relief, inserting the extension wire hadn't stuffed up the measurements at all.

Now we looked at how we were going to poke the sensor probe into the intake plenum.

We considered a couple of different methods of passing the probe through the metal blanking plate (including using a drilled-out bolt filled with high temperature epoxy), but the best of the alternatives was to buy a $5 brass compression gland. At least this way there was no risk of anything going wayward into the engine... However, because we couldn't source a specific gland to suit the 3.5mm OD of our sensor probe, we ended up having to drill out the 3.2mm ID centre of an otherwise perfect compression gland. This was of no concern though, as enlarging the bore slightly has no effect on how the olives inside the gland clasp down onto the probe.

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Next, we took our metal plenum blanking plate along to a local workshop to get it drilled and tapped to suit the new compression gland's 1/8 inch BSP tapered thread. It was a ten minute job at the most. However - following this - a bit of the threaded gland that was left protruding beyond the opposite face of the plate was ground off flush. This served to maximise the length of the probe that would be exposed to the intake air, rather than just being unnecessarily covered up by the thread. Note that the module's instruction page recommends that there is at least 10mm of the probe tip exposed into your test medium - we ended up with about 18mm poking through. No probs.

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After nipping up the heads on the gland to tighten the internal olives down onto the sensor probe, we then re-installed the tapped plate into the bottom of the intake manifold. The very last job was to cable-tie the connecting wire out of the way, and ensure there was no tension pulling on the cable where it went into the top of sensor probe (a notoriously weak area on this type of probe).

The Fruits...

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Having spent a grand total of $45, we've got for ourselves a nicely integrated digital display that works across the entire intake temperature range. The display reacts very briskly to changes of temperature of the incoming air, and that one second sample rate is perfect for instantaneous sampling. It's also interesting watching the temperature patterns that appear in relation to heat-soak, throttle position, plus - of course - ambient temperature. And, once we'd set the high temp alarm to our desired setting, there's been absolutely no need to access the buttons on the back of the display (although we may use the peak recall function when we do our planned intercooler testing).

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To date, we're pleased that we haven't had any worries with the LCD screen going black when the cabin gets nasty-hot - unlike some other digital displays. The only downside is that the unit isn't back-lit, or of the LED variety. Still - if you chose to - you can illuminate the display by aiming a coloured LED down over the face of the screen (although there will be some stray light scatter). That aside, what more could you possibly want for a measly 40 dollars?

Contact:

Now available in the AutoSpeed Online Shop

Jaycar Electronics
www.jaycar.com.au

Industrial Pyrometers (compression gland)
+61 8 8352 3688

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