MOPED ARMY

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

Here you go pretty cheap.

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.

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.

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.

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.

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. .

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?

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!

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

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.

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 😕

i hope theres a button to switch from celcius

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....