A working temperature gauge

[agent_orange]

Hey Binary,

I have a challenge for you which I hope you would like to accept.

As most of us know, the temperature gauge on MX5's do not tell you the actual temperature. All it will do is tell you "is the temperature ok? Yes or No". Adding a proper sensor is not terribly difficult. MM has posted a How To on this I believe. However the challenge seems to be finding a way of delivering this new info to the dash board. The simple way is ofcourse to install a new gauge, but personally I would hate having the old dial still sitting there being useless.

So BinaryPunk, is it possible to modify the existing Temperature dial to accept readings from an accurate sensor installed by ones' self? Or what would be the necessary steps to "upgrade" the dial in order to make use of a new sensor?

Cheers

[BenF]

[Mazda Mender]

The gauge is dampered.
M-m

[binarypunk]

Well...the gauge is actually just as accurate as any other. It's uncalibrated, yes - but with a thermometer and some tippex, that could be easily fixed. The issue with the stock gauge is that it has a gigantic flat-spot, so everything from 'warm' to 'really quite hot' all reads as pretty much in the middle. It does move, and given a magnifying glass and some concentration you can see it climb, but it's not very useful all in all.

Not a lot that's practical can be done about that, I'm afraid.

However, there is a perfect answer. My dash warning light kits are able to read the stock sender level extremely accurately, so the temp light comes on long before the change is visible on the gauge. Plus, a bright red light attracts your attention a lot better than a gauge - however accurate it is.

[Mazda Mender]

Nowt like a good old fashioned plug Jon
I for one can vouch for Jons kits form fitting them myself, there is a how to being built on how to fit them to the MK 2's and Mk 1's, but my camera card as crashed? and i have lost a 1000 pics for a shed load of how to's, so i will finish it Jon when i can get around to taking more pics
M-m

[agent_orange]

@Binary Well to be honest the only reason for me wanting this is to have something to scream at me when the engines running hot. So your good old fashioned plug sounds just the ticket.

@MM Dont give up on those photos, let me work my magic on that memory card.

[Mazda Mender]

let me work my magic on that memory card.

Hurry up then, i know that the MK 2 to the MK 2.5 nose cone swap is also on it plus god knows what else as i have been going along.
M-m

[agent_orange]

let me work my magic on that memory card.

Hurry up then, i know that the MK 2 to the MK 2.5 nose cone swap is also on it plus god knows what else as i have been going along.
M-m

Il do it when I see you on Sat

[binarypunk]

to have something to scream at me when the engines running hot.

Then the warning light is just the ticket. Even the most accurate gauge in the world is no good at attracting attention....a red light is hard to miss.

[Lazza]

It is possible to modify the existing gauge to show the correct temperature using some resistors/diodes whatever they are. Mine was done but doesn't work
Of course there are no numbers on the gauge but it can be made to move in the correct linear fashion. Details are on the web somewhere. Probably on Nutz.

[binarypunk]

I've seen this before which appears to squash the curve a little to make it appear more linear, is this the sort of thing that was done?

[Lazza]

That looks like it. Its different for different models so needs different combinations of resistors/diodes.

[paggers]

Jon - are you thinking of building an option for this into your microprocessor kit? I was thinking that it wouldn't be too hard to build some code that would take the input voltage from the temperature sensor and use it to drive a variable output voltage at the correct levels to give the gauge a more linear appearance (would certainly be a lot simpler and easier to tune than all those resistors etc).

If you do have this on the drawing board say so as otherwise I reckon I might have a tinker myself but no sense if you are about to produce one!

[binarypunk]

Certainly no plans in the near future.

There would need to be a major change, as the existing circuit can't produce analogue voltages, so I would need to implement a D/A converter somehow. Seeing as we're dealing with largish voltages (relative to the microcontroller) then it would also need amplification. This solution with the added resistors is far simpler to achieve than trying to remap voltages digitally... I have looked at whether there is a simpler way to just splice a circuit in, but it's no simpler and by the time you're desoldering components, you may as well carry on and just solder in new ones.

Another option is to use op-amps and filters to (de)amplify the voltages in certain ranges, but the design that would need to go into that is quite significant and brings me on to a more fundamental point:

Personally, if I was designing that gauge, like every other car designer in the world, I would create the same flat spot. This is absolutely a standard design practice to reflect the fact that there is a wide range of temperatures that should be considered 'normal' and only temperatures outside that range should be brought to the driver's attention. Every temperature gauge in every 'consumer' car does this.

The problem with the gauge in my eyes is not that it has a flat spot, it's that it isn't noticeable when it does move off the middle. This is the reason why I created a warning light, which draws your attention to the problem LONG before (any) gauge can. It can also be far more accurate (a few millivolts 'above normal' is all that is required before the control box spots the problem - at this point the gauge, modded or not, will have moved a distance of the order of about 0.1mm).

So, since the existing product solves both the problem of accuracy and noticeability (rendering the gauge pretty much redundant) I'm not keen to produce another solution to the accuracy 'problem' (that I personally don't see as a problem), which doesn't address the fundamental issue of hooning along with your gauge against the stop, and never seeing it until it's too late and you have a warped head on your hands. Accuracy of readout is a matter of interest (and needless distraction) for the driver, noticing that your car is overheating is a matter of saving your engine...

[Lazza]

To be honest, I think that converting the gauge to an oil pressure gauge (like the early Mk1s) would be a much more useful and interesting mod