Can I make an analog temp guage?

I’m reading these recent posts about temp gauges. I always wanted one, but refuse to pay the price for the trail tech. It’s a $10 piece (by my pricing biases) and I won’t cough up the cash.

I googled the spark plug thermocouple. <$10

I googled an analog auto voltmeter ~$12

If a person was to use the thermocouple as it is, a heat-varied resistor, reverse polarity, and bench test to create a new scale for the gauge faceplate, would it reasonably display temp?

It would need its own clean power source.

Yes it’s more trouble. I’m a rebel damnit.

Re: Can I make an analog temp guage?

Yep, that's about all they are. The thermistor they use is industry standard so someone might already sell a calibrated gauge.

A 3v lithium cell should be plenty, I'm sure an analog gauge will burn slightly more current but those squatty camera batteries would probably last a very long time.

If you come up with something post it up, I'd like to find a cheaper source for the spark plug ring terminal/ sensor.

Re: Can I make an analog temp guage?

I used ultralight airplane gauges for my old rd. All analog

Re: Can I make an analog temp guage?

Airplane? Aren’t all avionics issued two extra zeros on the price just because?

I’ll see what I can do. I’ll be sure to post if it’s a fail or success. Not too worried about power consumption since it would just be for tuning. Once the thing is set, I can easily feel a change. Maybe click it on momentarily during hard pulls for peace of mind.

Re: Can I make an analog temp guage?

Here you go pretty cheap.

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Re: Can I make an analog temp guage?

Not real fast acting but good for keeping an eye on things.

Re: Can I make an analog temp guage?

That’s still a little pricey... buuuuuut

I would feel cool about airplane parts on my moped.

Could tip the scales in that direction.

For now I’m gonna start with the cheap-ass version just to see if it works and share that with all the other cheap-ass moped people I know are on here.

Re: Can I make an analog temp guage?

Amazon deals. $20 for both with shipping. It’s gonna take months to get to me. Don’t hold your breath.

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Re: Can I make an analog temp guage?

> Papa _ Wrote:

> -------------------------------------------------------

> Amazon deals. $20 for both with shipping. It’s gonna take months to get

> to me. Don’t hold your breath.

Thing is, the meter reads volts and the thermostat couple puts out a variable resistance depending on the temperature it senses.

Just curious what plans you have to hook the two together.

Love to know.

Re: Can I make an analog temp guage?

Easy - just get a type K thermocouple and a dial for millivolts, then check for the chart for the k-type and plot from zero to 50mv for minus 18 to 2500 degrees f for a EGT gauge. 500 degrees is like 10mv so you need to plot that if you are doing CHT.

Re: Can I make an analog temp guage?

Rebel seems to know more about it specifically than I do.

I was just running with the idea that the thermocouple decreased resistance as heat increases. Which would cause a measured increase on the voltmeter.

The meter I bought was for 0-15VDC. So, according to Rebel, I’ll never see it budge if the varied resistance Going to cause <10mV range.

Maybe have to get a mV scaled meter or hack the one I bought. Won’t know until I get ahold of it and try some stuff.

Re: Can I make an analog temp guage?

Terbo Speghetti /

Following this. I had this thought, but I wanted to add a second thermistor on one of the exhaust studs for a more complete look at your temps.

Re: Can I make an analog temp guage?

That was I was referring to. I’m an electrical engineer so I get the physics of the situation. I was referring to the post where you showed the 0-15 VDC dial voltmeter; usually used to check the state of a 12 VDC (nominal) battery.

A posible way would be to use a simple voltage divider circuit with the thermocouple and a scalable resistor in series. Get a volt meter in millivolts and read the voltage drop across the scalable resistor to adjust the meter. The scalable resistor could be a simple potentiometer. Once the meter is calibrated it might be wise to read the resistance of the potentiometer and replace it with a fixed resistor to avoid it shaking out of adjustment from vibration.

Just an idea off the top of the head.

> Papa _ Wrote:

> -------------------------------------------------------

> Rebel seems to know more about it specifically than I do.

>

> I was just running with the idea that the thermocouple decreased

> resistance as heat increases. Which would cause a measured increase on

> the voltmeter.

>

> The meter I bought was for 0-15VDC. So, according to Rebel, I’ll never

> see it budge if the varied resistance Going to cause <10mV range.

>

> Maybe have to get a mV scaled meter or hack the one I bought. Won’t know

> until I get ahold of it and try some stuff.

Re: Can I make an analog temp guage?

Thanks Jai Dot.

I’m an electronics maintainer. So, definitely not qualified to engineer things. But, familiarity with components makes me feel brave.

I am assuming that the electromagnet driving the needle on my gauge is the same as many others. Scaling accomplished by resistors and such inside like a multimeter.

Re: Can I make an analog temp guage?

An issue to consider is that the response of the sensor to heat is not linear. So you need to match the response curve of the sensor to metering device. Also consider that the voltage across the meter’s terminals will vary depending on the pole voltage of the circuit’s voltage source.

If you want to tinker with a meter maybe consider using an auto temperature gauge (analog meter) That you can get cheap from an auto parts store. They are already ready ranged to around 300 degrees at the upper limit of the meter and usually don’t come with number readout. Rather they use a green zone/red zone indication. They also have an analog response to better match the thermistor’s value. Using a standard voltmeter that has a linear response will require you to compensate for the response curve of the thermistor with additional circuit components. .

Re: Can I make an analog temp guage?

I was just going to have a custom, wonky scale if needed. Mark the dial at 200,300,400,500. Wherever the needle may be at those temps. Not perfect, but functional.

If I get the parts and a skeleton of it working, maybe y’all can help me make it nice.

My current MO is to carry my IR temp gun and stop quick to shoot the head after a WOT run. Which is not accurate but for tuning I can see 260* as: “it probably didn’t cool down that much.” and 320* as: “dang that could have been pretty high 20 seconds ago.”

Hell, if the gauge is a flop, maybe just build a circuit that turns an “over temp” light on at a set point. Have that be adjustable.

Re: Can I make an analog temp guage?

I did a thing today.

My Thermocouple came in finally. Pics show my test setup. I just turned the stove on for a few seconds and then back off. The temp would rise and settle. Then, I shot the temp at the base of the spark plug to see what the head temp was.

Recorded the voltage displayed w/the temps on the way up (slowly increasing heat to not crack the stove top) and then recorded the temps and voltage on the way back down as the head cooled.

Voltages were lower on the way up because the heat wasn’t fully conducted into the thermocouple as the head temp was rising. I wanted an average of those values.

So, my numbers are:

200*F - 2.6mV

250 - 3.6

300 - 4.8

350 - 6.0

400 - 6.9

450 - 7.6

(these values are about 1.25mV off from listed values for K type thermocouple. I assume my non-calibrated multimeter and IR thermometer are to blame)

I want to make a tiny LED bar right under my speedo that goes: Blue, Green, Green, Yellow, Orange, Red. Corresponding to the temps listed above. Or something along those lines. You get it.

So, do any of you electrical engineers know what transistor or component I would need to turn on a circuit with 2-8mV?

I am envisioning building a test rig with variable resistor that I can adjust to turn on a amplifying transistor thing at say ~ 4.8mV and then measuring resistance of that. Then using plain old resitors in the actual build. Repeating that process for each LED/temp.

Does that make sense? Anyone out there think they can help me do this? Or know an off the shelf LED guage that might operate at this voltage range?

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Re: Can I make an analog temp guage?

Maybe I should take the cheap and easy way out and just mount a mV meter.

It can’t be too hard to remember what voltage corresponds to what temp.

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Re: Can I make an analog temp guage?

I get the thrill of the project here, but the trailtech is $43 right now. so, during a sale that would be $34.

found the YC101297 for $33 on wish. or even gamble on this

so if you wanted to find another $13, you could be tuning by EGT - since it would just be for tuning or hard pulls as you said. depending on what your state of tune is, and your definition of a "hard pull" - there is a chance to seize up before your CHT has a chance to even register.

would I pay $50 for a trailtech CHT gauge? no. but, I also wouldn't bother with CHT. and, I would pay triple that to get a quality digital pyrometer setup from The Sensor Connection. and I also have access to a dyno for tuning. so, that's my personal context FWIW.

Just a perspective - good luck & have fun!

Re: Can I make an analog temp guage?

Steve,

You are not wrong.

I am doing this for the sake of DIY and to save some $

The temps take like ~10 seconds to “update” based on my stovetop test.

I think it would be good to optimize timing and jetting. Safe in the hands of an experienced tuner. Maybe a false sense of security to a newb.

i feel like a $10-15 finished product is possible.

I am not a racer. So, my needs are simple enough. Just want a fast moped that doesn’t break down. Tuning by ear and by feel, always playing it safe with rich plug chops. I think this would allow me to get a little more out of my ride.

Re: Can I make an analog temp guage?

If you are doing a CHT gauge then use a J thermocouple (iron/constantine junction) so it is more scalable for the temperature range (though 600f you would know because your rear wheel would likely be locked at that point). Plot the data points on a blanked out background for the gauge with the temperatures.

Best practice is to mount an analogue gauge with "normal" pointing straight ahead, you are looking for ease of reading more than something that looks good to someone not riding. With the needle "straight ahead" you can tell at a quick glance if you are in trouble, rather than trying to 'read' where the needle is...

Data points for the J thermocouple

Deg F....... Millivolt

100F........ .72mv

200F........ 3.69mv

300F........ 6.72mv

400F........ 9.81mv

500F........ 12.9mv

600F........ 15.96mv

Re: Can I make an analog temp guage?

I looked at analog guages. From my experience at work, I was worried that it would be very unstable on a vehicle in motion. As in, the needle swinging around from every little movement.

I think I am gonna go the millivolt meter route though. Digital. See if it does what I expect when installed on the running engine.

I did buy the analog guage posted earlier. As was pointed out by Jai Dot, it is a Volt meter, not millivolt. I would have to amplify the output of my thermocouple to drive that guage. Then make a custom faceplate with my temps marked.

Probably doable. I’ll let you know if I get something to work. Give me a few days/weeks on this one.

Re: Can I make an analog temp guage?

EE here, if it were me I'd do something like this:

Use a chip specifically designed to make reading K-type thermocouples easier, probably the AD8495 https://www.analog.com/en/products/ad8495.html#product-overview

Put the output of that chip into an ADC on a micro controller

Have the microcontroller drive a screen

This would be super simple and cheap with an arduino or an esp32

That's not purely "analog" but it'd be pretty straightforward.

Re: Can I make an analog temp guage?

> Brian F Wrote:

> -------------------------------------------------------

> EE here, if it were me I'd do something like this:

>

> Use a chip specifically designed to make reading K-type thermocouples

> easier, probably the AD8495

Yeah that's the one I'm using with my dyno. I have it running into an arduino but it just runs straight analog out. You'd just need to give it clean power, even a 9v battery would be fine, and maybe set up some kind of voltage divider to get the right range for your gauge, but you ought to be able to get it to drive a gauge.

https://www.adafruit.com/product/1778

Re: Can I make an analog temp guage?

So, all my internet searching a research finally provided a result.

Logic says if the components can be purchased for a few dollars, that there is an assembled version for cheap as well.

After using the wording: “thermocouple display unit” - since no other words yeild the desired item - I finally found it.

It even comes with a K type threaded sensor. So, I bought two. One will swap the head temp, spark plug sensor. The other will get a mount welded to my header for EGT.

Thanks for all the smart guys giving DIY advice. I would still go that route, but it would cost more than $10 to make it happen. So... kinda perfect package here.

Shipping from China. I’ll update this in a month or two 😕

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Re: Can I make an analog temp guage?

Let's not forget to mention that it has big ol seven segment displays. Which is sweeeeeeeet

Re: Can I make an analog temp guage?

i hope theres a button to switch from celcius

Re: Can I make an analog temp guage?

I feel like, as a species, it is time for us all to move on to metric measurements.

I have been living (and cooking) in Germany long enough now that my brain can understand a temp given in C instead of F.

It would be nice to have an option. But... the world isn’t really concerned with catering to silly Americans any more.

*PLUS*

In celsius, I will get to pass 88* while accelerating. Give those Back to the Future vibes. Aaron will appreciate that for sure.

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Re: Can I make an analog temp guage?

Yeah being in engineering it sucks, at my old job I would have to draw 2 sets of prints for everything because they wanted to make in US or outsource to China, and it wouldn't be a big deal to just change the numbers but you have to change all the stock material sizes because they don't have 68.546mm tubing sitting on the shelf over there. Half the time I'm having to draw metric shit in english so the shops here can make it, or english shit in metric. To make matters worse it's called 'standard' even though it's not standard to anything....

Re: Can I make an analog temp guage?

Our old school 'standard' measure chief engineer retired, our new chief engineer is very bothered by the 'standard' shyte that was designed, fabricated and appended to machines which are metric. Slowly getting rid of the 'standard' shyte and replacing it with metric (YAY) makes life so much easier.

> Graham Motzing Wrote:

> -------------------------------------------------------

> Yeah being in engineering it sucks, at my old job I would have to draw 2

> sets of prints for everything because they wanted to make in US or

> outsource to China, and it wouldn't be a big deal to just change the

> numbers but you have to change all the stock material sizes because they

> don't have 68.546mm tubing sitting on the shelf over there. Half the

> time I'm having to draw metric shit in english so the shops here can

> make it, or english shit in metric. To make matters worse it's called

> 'standard' even though it's not standard to anything....

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