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Old 07-14-2010, 12:37 PM   #1
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Default DIY digital temp gauges

I've always wanted dual digital gauges, but not for $300 (Spa brand):

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If someone can find an inexpensive (~15) LCD backlit green voltmeter panel gauge of the right size, I will design a circuit to read off of the factory water temp signal, and off of a $1 oil temp thermistor so it will read oil and water temps. An EGT circuit is easy too.

The panel meters have to be small enough to stack 2 vertically by 3 wide in the miata's panel below the stereo.

Here is what I mean by panel voltmeters:


However in this example (a) it has no backlight and (b) it is too tall to stack 2 vertically.

With small enough meters, one could replace the factory temp gauge in the dash with dual oil and water temp too....

FWIW backlit LCD is better than LED because the latter is hard to read in sunlight.
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Old 07-14-2010, 12:41 PM   #2
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Old 07-14-2010, 01:01 PM   #3
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Nice find but, it's:
- LED
- you need to install its senders ($18 each)
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Old 07-14-2010, 05:34 PM   #4
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I had some panel voltmeters I converted to read Wideband 0-5V signals and turn them into AFR.

Jason: can you post up a schematic for the "share the sensor" circuit for water temp?
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Old 07-14-2010, 07:35 PM   #5
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I haven't designed it yet
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Old 07-15-2010, 10:16 AM   #6
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Quote:
Originally Posted by JasonC SBB View Post
Nice find but, it's:
- LED
- you need to install its senders ($18 each)
i know, just giving you the option. i bet you could get the same senders for $3 each.


maybe i could get shuiend to measure the scale of his?
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Old 07-15-2010, 10:51 AM   #7
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Quote:
Originally Posted by Braineack View Post
maybe i could get shuiend to measure the scale of his?
NEVARZ. Ok what do I need to measure and what is the easiest way to do it?
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Old 07-15-2010, 10:59 AM   #8
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http://www.diyautotune.com/tech_arti...alculation.htm


something like that. the body of the sensor is ground. I'm sure they are a generic sender you can pick up for a song. I dunno...
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Old 07-15-2010, 11:17 AM   #9
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That looks like so much work. It might possibly happen, we will see.
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Old 07-15-2010, 11:34 AM   #10
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exactly.
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Old 07-15-2010, 12:32 PM   #11
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If it's been installed already, just unplug the harness and read the resistance when:
The engine is at room temp.
The engine is partially warmed up.
The engine is hot.
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Old 07-15-2010, 12:35 PM   #12
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I'd be interested in these DIY temp gauges.
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Old 07-15-2010, 01:22 PM   #13
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Quote:
Originally Posted by Braineack View Post
BTW how easy are these to read in sunlight?
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Old 07-15-2010, 02:09 PM   #14
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based on innovate DB gauge...going with: impossible.
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Old 07-15-2010, 02:16 PM   #15
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Quote:
Originally Posted by JasonC SBB View Post
If it's been installed already, just unplug the harness and read the resistance when:
The engine is at room temp.
The engine is partially warmed up.
The engine is hot.
Um they are sitting in my engine on my engine stand. I might pull one out to test the sender tonight. I just need to find a thermometer tonight.

Quote:
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BTW how easy are these to read in sunlight?
That I do not know, I just bought the 2 senders for now. When I am done with my engine build and have spare money I will pick up the gauges.
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Old 07-15-2010, 02:19 PM   #16
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i was kinda sad after i replaced my narrowband gauge for the DB (same as blue pictured above, mines red) the first time i drove with the top down. so i enabled the AFR safety code.
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Old 01-23-2011, 02:43 PM   #17
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Quote:
Originally Posted by JasonC SBB View Post
With small enough meters, one could replace the factory temp gauge in the dash with dual oil and water temp too....
For posterity's sake, I measured the factory temp gauge in my '00 cluster. Diameter of the visible area is 1.67", depth of the gauge itself is 1.2".
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Old 01-29-2011, 07:00 PM   #18
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2 of these stacked vertically would juuuust fit, but no backlight!




http://www.lumex.com/specs/LCD-S2X1C50TR.pdf

$3 at Digikey:
http://parts.digikey.com/1/parts/679...s2x1c50tr.html
That one is reflective.

Here's the "trans-reflective" version of the same thing:
http://search.digikey.com/scripts/Dk...ame=67-1798-ND

Trans-reflective means you can read it with ambient light, *and* you can also backlight 'em.
I just might buy some to play with it, see if I can add backlighting.
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Old 01-29-2011, 07:18 PM   #19
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Very nice looking unit, and the backlight modules are pretty cheap as well.

One thing that occurs to me about the specific units you posted, at least in a temperature-reading application, is that they can only display a maximum reading of 199. Well, actually that's not true; they could display a maximum value of 511, but only if you enjoy doing hex-to-decimal conversion in your head in realtime.

They do have three-digit units which fit in essentially the same outline, though the characters are much smaller and are spaced out a great deal more. http://search.digikey.com/scripts/Dk...rds=67-1799-ND

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Old 01-29-2011, 07:33 PM   #20
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I will display in Celsius.
Remembering "100*C" = boiling and "120*C" = "freaking hot" is easy.

Here's a 128x64 dot matrix, serial comm, includes the backlight. Perhaps it can be shoehorned in the gauge cluster:
http://www.sparkfun.com/products/710


Dimensions:
Overall: 75 x 53 mm
Viewable area: 55 x 27.5 mm

Of course only a portion of it will show, but that's enough to display oil and water temps

And they have LCD's galore:
http://www.sparkfun.com/categories/148
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