Vehicle engine temperature display

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
First post and a polite hello.

I have purchased a vehicle which was not built with a temperature gauge....yeh I know, but it has been under my care for many years.

As a now retired mechanic no temperature reading is bloody annoying with my old way of thinking, there is no room to fit a gauge and I do not want something aftermarket hanging from the windscreen pillar.

All I want on the dashboard is an LED (5mm?) that is perhaps blue when the engine is cold below say 65°C? It then goes out unless the engine starts to get too hot for example 110°C and then a either turns red or have a second LED?

I can access the OE on board computer to read the actual engine temperature but it's a lot of faffing about and is really for diagnostic use, so a KISS approach is wanted.

I have done 'stuff' like this in the past, but after brain surgery I no longer have the ability to concentrate, or have the patience/steady hand to build what I require. So looking for assistance from forum members, perhaps something that can be purchased pre fabricated.

As the vehicle probably already has enough electronics to control the space shuttle, I would rather something that is standalone and not tied in with any of the vehicles standard equipment.

Assistance in this matter would be appreciated.

Please note, I live in Spain so apologies if there is a delay in replying due to time zone differences.

Many thanks.

Regards

Dave.
 

MrChips

Joined Oct 2, 2009
30,815
Hello, Hello.

We receive dozens or more new threads each day. You can help other readers by posting a thread title with much more than just "Hello". The thread subject title should give readers a glimpse of what is the nature of the thread. A title such as "Vehicle temperature display" would be a suitable title.
 

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
Hello, Hello.

We receive dozens or more new threads each day. You can help other readers by posting a thread title with much more than just "Hello". The thread subject title should give readers a glimpse of what is the nature of the thread. A title such as "Vehicle temperature display" would be a suitable title.

Yes your absolutely right, I did look for an introduction section on the forum list but must have missed it?

I am unsure if I can change the title but will give it a go.

Regards

Dave.
 

dl324

Joined Mar 30, 2015
16,924
Welcome to AAC!

All I want on the dashboard is an LED (5mm?) that is perhaps blue when the engine is cold below say 65°C? It then goes out unless the engine starts to get too hot for example 110°C and then a either turns red or have a second LED?
What you want should be straightforward once you've clarified your requirements.

You say the LED should be blue when the engine is below 65C and it should go out when the engine starts. Does that mean the LED is off when the engine is off? Having it be on for a period of time when the engine is first started would make more sense.

A temperature sensor, timer, and a couple comparators should do it.
 

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
First post and a polite hello.

I have purchased a vehicle which was not built with a temperature gauge....yeh I know, but it has been under my care for many years.

As a now retired mechanic no temperature reading is bloody annoying with my old way of thinking, there is no room to fit a gauge and I do not want something aftermarket hanging from the windscreen pillar.

All I want on the dashboard is an LED (5mm?) that is perhaps blue when the engine is cold below say 65°C? It then goes out unless the engine starts to get too hot for example 110°C and then a either turns red or have a second LED?

I can access the OE on board computer to read the actual engine temperature but it's a lot of faffing about and is really for diagnostic use, so a KISS approach is wanted.

I have done 'stuff' like this in the past, but after brain surgery I no longer have the ability to concentrate, or have the patience/steady hand to build what I require. So looking for assistance from forum members, perhaps something that can be purchased pre fabricated.

As the vehicle probably already has enough electronics to control the space shuttle, I would rather something that is standalone and not tied in with any of the vehicles standard equipment.

Assistance in this matter would be appreciated.

Please note, I live in Spain so apologies if there is a delay in replying due to time zone differences.

Many thanks.

Regards

Dave.
Welcome to AAC!

What you want should be straightforward once you've clarified your requirements.

You say the LED should be blue when the engine is below 65C and it should go out when the engine starts. Does that mean the LED is off when the engine is off? Having it be on for a period of time when the engine is first started would make more sense.

A temperature sensor, timer, and a couple comparators should do it.
Thank you for your reply.

Enter car, LED is off, start engine which happens to be below 65°C, Blue LED advises this fact.

Drive vehicle, engine reaches 65°C Blue LED goes out, and remains out unless for some reason engine gets too hot, in which case a red LED lights up advising a more serious problem.

Unsure why there would be a timer?

I hope that explains my requirements?

Regards

Dave.
 

crutschow

Joined Mar 14, 2008
34,454
I have done 'stuff' like this in the past, but after brain surgery I no longer have the ability to concentrate, or have the patience/steady hand to build what I require. So looking for assistance from forum members, perhaps something that can be purchased pre fabricated.
I did a quick search, but found nothing already built that would meet your needs.
So I think you will either need to build something yourself, or live with one of the add-on gauges that can be purchased.
 

Externet

Joined Nov 29, 2005
2,221
This one works only to 110C ----> https://www.temu.com/celsius-aquari...&refer_page_id=10009_1708824288662_h4zotnyiuw

I installed one of these in my vehicle that suffers from the same crap with no dash thermometer; just an idiot pointer ----> https://www.temu.com/1pc-meat-therm...&refer_page_id=10009_1708824767100_vkorprtx9g

Another of the same ----> https://www.ebay.com/itm/2759914248...5HAnXWv9l42RnAIQG5WGfSZ48A%3D%3D|ampid:PL_CLK

Highly recommended, have settable alarm, 1 AAA battery lasts 1 year !.
 

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
Because you said this

With the clarified requirements, you need a window comparator for the blue LED and probably one to indicate over temperature.
Thank you for the reply however, it still does not answer the reason for a timer?

If the engine starts to get too hot, red LED comes on and I switch off the engine too investigate......no timer.

I could easily fit a sensor in one of the hoses attached to the cylinder head, it could activate an LED if the engine reached an undesired temperature. But I would prefer a system that indicates too low a temperature, and once the engine reaches normal operating temperature the LED stays out. Only an engine close to overheating would bring on a red LED.

Again thanks for any input.

Regards

Dave
 
If you can fit an NTC sensor and you have details of the temperature/resistance curve then you could use a single RGB LED to drive blue or red according to the relevant resistance thresholds using two comparators a already suggested. I’d recommend a small amount of built in hysteresis to prevent flickering as the temperature hovers close to the limit points but that may not be necessary.

Have a look at the TI “comparator with hysteresis reference design”. I don’t know how to add a link from my phone! Connect the sensor in series with a resistor equal to around the resistance of the sensor half way between 65 and 110 degrees to create a potential divider and link the mid point to the +ve input of one comparator and the - ve input of the other. With fixed resistor potential dividers connected to the other inputs of the comparators the outputs will swing between the positive rail and ground which can drive the RGB LED to achieve what you are looking for.

Fairly simple to build, but you can buy LM393 comparator modules online very inexpensively which have trimpots to adjust the trigger voltage. You can calibrate by using fixed resistor values in place of the sensor.

Just to say, I like the idea of an indicator to show low temperature - it encourages gentle acceleration when the engine is cold, for a longer engine life. If you can post the temperature/resistance curve of the sensor you want to use I’d be happy to sketch the circuit with component values.
 

Sensacell

Joined Jun 19, 2012
3,449
I would use a micro.

For sure you will need to mess around with setpoints and calibration stuff - all of which is nightmarish in hardware.
If you do it digital, you can fiddle with the functionality to your hearts content without having to rip things open every time, just download new code and try again.

There are plenty of really simple digital temp sensors to choose from, and perhaps you can use a digital WS2811 based RGB LED, which only needs 3 wires. (Neopixel)
 
Last edited:

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
If you can fit an NTC sensor and you have details of the temperature/resistance curve then you could use a single RGB LED to drive blue or red according to the relevant resistance thresholds using two comparators a already suggested. I’d recommend a small amount of built in hysteresis to prevent flickering as the temperature hovers close to the limit points but that may not be necessary.

Have a look at the TI “comparator with hysteresis reference design”. I don’t know how to add a link from my phone! Connect the sensor in series with a resistor equal to around the resistance of the sensor half way between 65 and 110 degrees to create a potential divider and link the mid point to the +ve input of one comparator and the - ve input of the other. With fixed resistor potential dividers connected to the other inputs of the comparators the outputs will swing between the positive rail and ground which can drive the RGB LED to achieve what you are looking for.

Fairly simple to build, but you can buy LM393 comparator modules online very inexpensively which have trimpots to adjust the trigger voltage. You can calibrate by using fixed resistor values in place of the sensor.

Just to say, I like the idea of an indicator to show low temperature - it encourages gentle acceleration when the engine is cold, for a longer engine life. If you can post the temperature/resistance curve of the sensor you want to use I’d be happy to sketch the circuit with component values.
I would use a micro.

For sure you will need to mess around with setpoints and calibration stuff - all of which is nightmarish in hardware.
If you do it digital, you can fiddle with the functionality to your hearts content without having to rip things open every time, just download new code and try again.

There are plenty of really simple digital temp sensors to choose from, and perhaps you can use a digital WS2811 based RGB LED, which only needs 3 wires. (Neopixel)
Great replies and genuinely appreciated.

I certainly am looking for something already or close to being constructed.

Years ago I could work out things like this myself, but not any longer. After brain surgery it to me over two years to get my driving licence back. Epilepsy has along with other problems have continued to plague me, now I have something to reference with I have somewhere to start.

Again many thanks.

Regards

Dave.
 

dl324

Joined Mar 30, 2015
16,924
Unsure why there would be a timer?
It's because the requirements in your initial post were unclear to me. You said
All I want on the dashboard is an LED (5mm?) that is perhaps blue when the engine is cold below say 65°C? It then goes out unless the engine starts to get too hot for example 110°C and then a either turns red or have a second LED?
By saying "then it goes out unless the engine starts to get too hot" could be interpreted to mean that it wasn't to stay on until the temperature got to 65C; hence the need for a timer.

If you want it to stay on as long as the engine is 65C or less, you should have said that instead of saying it goes out (presumably after some time) and the other LED (presumably red) will come on when the engine gets hot (115C).

"When the engine is running, the Blue LED stays on until temperature reaches 65C. Red LED turns on when temperature is above 110C."

I couldn't design a circuit for you until I understood the requirements.
1708880278617.png
In this circuit, the blue LED will be on until the voltage from the temperature sensor gets up to whatever voltage represents 65C. At that point, the blue LED will go out and neither LED will be on. When the temperature gets to 110C, the red LED will be turned on.

If you use a common anode RGB LED, you only need one LED. I used an LM339 instead of LM393 in case you need to amplify the output of the temperature sensor. The comparators allow inputs near ground, but the highest input voltage is limited to 1.5V below the supply voltage. Zener voltage depends on the voltage range needed for the trip points. R2-4 set the trip points. R5 must limit LED current to 6-16mA (6mA is guaranteed, 16mA is typical).

If slow temperature transitions cause the LEDs to blink, you can add hysteresis if it bothers you.
 
Last edited:

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
It's because the requirements in your initial post were unclear to me. You said

By saying "then it goes out unless the engine starts to get too hot" could be interpreted to mean that it wasn't to stay on until the temperature got to 65C; hence the need for a timer.

If you want it to stay on as long as the engine is 65C or less, you should have said that instead of saying it goes out (presumably after some time) and the other LED (presumably red) will come on when the engine gets hot (115C).

"When the engine is running, the Blue LED stays on until temperature reaches 65C. Red LED turns on when temperature is above 110C."

I couldn't design a circuit for you until I understood the requirements.
View attachment 316167
In this circuit, the blue LED will be on until the voltage from the temperature sensor gets up to whatever voltage represents 65C. At that point, the blue LED will go out and neither LED will be on. When the temperature gets to 110C, the red LED will be turned on.

If you use a common anode RGB LED, you only need one LED. I used an LM339 instead of LM393 in case you need to amplify the output of the temperature sensor. The comparators allow inputs near ground, but the highest input voltage is limited to 1.5V below the supply voltage. Zener voltage depends on the voltage range needed for the trip points. R2-4 set the trip points. R5 must limit LED current to 6-16mA (6mA is guaranteed, 16mA is typical).

If slow temperature transitions cause the LEDs to blink, you can add hysteresis if it bothers you.
Many thanks for the reply. I apologise if my explanation was not clear.

Many thanks for taking the time to make up the diagram, the engine temperature will continue to rise after it reaches 65°C (Blue LED now out) until it reaches its normal operating temperature which is 80°C - 90°C, so hysteresis should not be required, I prefer to use a single RGB LED, so have taken note of your comment.

Many thanks again for your assistance.

Regards

Dave.
 
View attachment 316167
In this circuit, the blue LED will be on until the voltage from the temperature sensor gets up to whatever voltage represents 65C. At that point, the blue LED will go out and neither LED will be on. When the temperature gets to 110C, the red LED will be turned on.

If you use a common anode RGB LED, you only need one LED. I used an LM339 instead of LM393 in case you need to amplify the output of the temperature sensor. The comparators allow inputs near ground, but the highest input voltage is limited to 1.5V below the supply voltage. Zener voltage depends on the voltage range needed for the trip points. R2-4 set the trip points. R5 must limit LED current to 6-16mA (6mA is guaranteed, 16mA is typical).

If slow temperature transitions cause the LEDs to blink, you can add hysteresis if it bothers you.
I question whether you should include the zener diode D1? The supply in a car can vary between about 12.0 volts, less when you have the starter motor running, and maybe 14.5 volts when the the alternator is running and charging the battery. And I think the "temp sensor" would be a potential divider with the NTC thermistor in series with a suitable fixed resistor connected between ground and the nominal 12V supply. That way, the the circuit should work with the variation in supply voltage at the same trigger temperatures
 

dl324

Joined Mar 30, 2015
16,924
I question whether you should include the zener diode D1?
The voltage will fluctuate depending on load and engine RPM. I certainly wouldn't want that type of variation in a temperature sensing circuit that depends on stable trip points. Especially when the parts in question will cost around a dime.

It depends on the accuracy the OP wants.
 

dl324

Joined Mar 30, 2015
16,924
I prefer to use a single RGB LED, so have taken note of your comment.
I would have used one in the schematic but didn't find anything.

If you want different currents in the LEDs, connect the anodes to power and put the resistors between the cathodes and comparator outputs.

I didn't show a supply decoupling cap. Use 0.1uF between the power pins. If you don't need to amplify the sensor output, you can use LM393 instead of LM339.
 

Thread Starter

Mechanic 2000

Joined Feb 24, 2024
9
I would have used one in the schematic but didn't find anything.

If you want different currents in the LEDs, connect the anodes to power and put the resistors between the cathodes and comparator outputs.

I didn't show a supply decoupling cap. Use 0.1uF between the power pins. If you don't need to amplify the sensor output, you can use LM393 instead of LM339.

Thank you for your reply and continued assistance.

Regards

Dave.
 
Top