No LM339 will be wasted as I couldn't do the shopping yet due to shortage of time, so I could buy different IC(s).
Still, I'll buy a few different ones listed by yourselves and start experimenting.

The sensor is a 2 wire job and it doesn't use the chassis ground.

I will open up my existing oil temp gauge hopefully tomorrow hoping to find the IC which handles the sensor and let you all know.
I am currently unable to measure voltage/resistance at the sensor while the gauge is working.

Using the existing sensor to drive both the gauge and this redline circuit would be great as I could save €30 by not buying a second one, but its not essential.

With the LEDs, I'm hoping to get square ones. I don't know if any high brightness models available of those, I'll research.
I don't need much brightness, but as you suggested, the LM339 might have a weak output to drive a normal LED.
When I get there to punch square holes into the dial, I might regret going square. If I can't get a decent solution to punch proper square holes, I'll downgrade the design to round holes/normal 5mm LEDs.

MisterBill2: You won't be able to talk me off of getting this done
I don't need such device, I know most aspects of lubricant temperature - load - rpm and wear. I just want a functional, unique eyecandy and the joy of building it with all your help.

Thanks for all the replies again!

 

No LM339 will be wasted as I couldn't do the shopping yet due to shortage of time, so I could buy different IC(s).
Still, I'll buy a few different ones listed by yourselves and start experimenting.

The sensor is a 2 wire job and it doesn't use the chassis ground.

I will open up my existing oil temp gauge hopefully tomorrow hoping to find the IC which handles the sensor and let you all know.
I am currently unable to measure voltage/resistance at the sensor while the gauge is working.

Using the existing sensor to drive both the gauge and this redline circuit would be great as I could save €30 by not buying a second one, but its not essential.

With the LEDs, I'm hoping to get square ones. I don't know if any high brightness models available of those, I'll research.
I don't need much brightness, but as you suggested, the LM339 might have a weak output to drive a normal LED.
When I get there to punch square holes into the dial, I might regret going square. If I can't get a decent solution to punch proper square holes, I'll downgrade the design to round holes/normal 5mm LEDs.

MisterBill2: You won't be able to talk me off of getting this done
I don't need such device, I know most aspects of lubricant temperature - load - rpm and wear. I just want a functional, unique eyecandy and the joy of building it with all your help.

Thanks for all the replies again!

There are smaller diameter LEDs available that would look better on your gage dial. Either 2.5 mm or 3mm, not sure which.

 

Opened up the gauge today, got some measurements.

I connected a 1K potentiometer to the sensor input and took voltage a resistance measurements at the terminals of the potentiometer.
The sensor ground and the gauge ground is common.

40C = 930‎Ω - 1.21V
45C = 790‎Ω - 1.10V
50C = 650‎Ω - 990mV
55C = 545‎Ω - 895mV
60C = 465‎Ω - 785mV
65C = 390‎Ω - 707mV
70C = 330‎Ω - 622mV
75C = 280‎Ω - 550mV
80C = 235‎Ω - 475mV
85C = 198‎Ω - 418mV
90C = 167‎Ω - 355mV
-----------------------
110C = 94‎Ω - 210mV
140C = 43‎Ω - 105mV

I found 3 ICs in the gauge. I think these are some custom chips, but here are what I found:
IC1: 358 ; 237A ; JRC written on it. - 2x4pin
IC2: TP-68L2 ; 505 ; D3J0 written on it. - 4x8pin
IC3: TP-6883 ; 3AAH0406 witten on it. - 2x8pin
The rest are passives, the traces are invisible.
There is also an unused 3 pin header inside. I was hoping there might be a changing voltage vs the sensor resistance, but it has 4.73V between pin 1 and 3 constantly.

Here are some pics:

Cheers

 

Depending on space available, surfaces mount LEDs might offer some advantages. I wrote this yesterday but forgot to hit Post.

 

OK, now the data is in! You can use the LM339 comparators and adjust them to give you 8 readings, about 5 degrees apart. You did not state if one side of the sensor is grounded, but it really does not matter much. I do recommend an instrument amplifier IC set for a gain of 4 to serve as a buffer to isolate the comparators from the temperature meter driver. With no hysteresis the comparators will dim slowly as the temperature rises, which will give the illusion of even better resolution. And you should use PNP transistors to drive the LEDs on the emitter side of the transistor, and have the comparator outputs fall as the temperature rises. That will remove the need for pull-up resistors, reducing the parts count a bit. Sorry that I can't provide a good drawing yet, I still don't have my CAD program running.

 

OK, now the data is in! You can use the LM339 comparators and adjust them to give you 8 readings, about 5 degrees apart. You

It seems the readings by the TS show a constant current of about 1mA
Don't the readings imply the sensor signal is linear?
If so, aren't we back to an LM3914?

did not state if one side of the sensor is grounded, but it really does not matter much. I do recommend an instrument amplifier IC set for a gain of 4 to serve as a buffer to isolate the comparators from the temperature meter driver. With no hysteresis the comparators will dim slowly as the temperature rises, which will give the illusion of even better resolution. And you should use

No hysteresis. What about oscillation?

An instrumentation amp would be best, but wouldn't a good RR dual opamp work?
a non-inverting opamp buffer and a non-inverting opamp for gain adjustment?
Just considering cost...

eT

 

It seems the readings by the TS show a constant current of about 1mA
Don't the readings imply the sensor signal is linear?
If so, aren't we back to an LM3914?



what about oscillation?



An instrumentation amp would be best, but wouldn't a good RR dual opamp work?
a non-inverting opamp buffer and a non-inverting opamp for gain adjustment?
Just considering cost...

eT

As a matter of fact, yes, without any hysteresis there probably would be some oscillation as thye voltage passed through the threshold level. That is why the LEDs would dim slowly as the temperature rose and the comparator outputs pulled low. But that would not be a problem provided that the power supply to the input amplifier was adequately isolated. And if it were an issue then adding a capacitor across the outputs. or as positive feedback, would solve the problem..

 

Took a couple more measurements, might be useful:
Voltage between the sensor pin 1 and 2(which is ground) without anything connected to it is 2.52V
Current flowing through the sensor wires at:
50C (650‎Ω) - 1.6mA
90C (‎167Ω) - 2.3mA
Min and Max currents measured at both extremes are 1.3mA and 2.7mA

DMM (Aneng AN8009) has no effect of the gauge display value vs set resistance at the potentiometer when I measure voltage or current.

MisterBill2: As for the ground question came up a few times, the gauge is connected to chassis ground (-) and 1 pin of the sensor is also connected to this ground at the gauge. The chassis plays no role between the sensor the gauge.

Bernard: I took a few pics of the tachometer. SMD LEDs might be the way, thanks.
The TO3P is for size reference. The gaps between the divisions are 5.5mm (0.216")
Putting square holes into the acrylic (backing/lightpipe) will be impossible. If I go square LEDs, the acrylic will get round holes and LEDs will pressfit in those. The dial face will get will get square holes somehow.

eT, Bernard, MisterBill2, dl324: Many of the terms such as gain, RR opamp I don't understand. If you have any part numbers in mind for various circuit ideas please let me know and I order them. I have ~ €50 for this project. If I don't have to buy a second sensor for €30, I think it's plenty. I can and will extend the budget if needed.
I have plenty of common value metal film (0.25W, 1%) resistors, plenty quality caps and a breadboard already. I never used the latter, but I'll figure it out.

Thank you

 

Took a couple more measurements, might be useful:
Voltage between the sensor pin 1 and 2(which is ground) without anything connected to it is 2.52V
Current flowing through the sensor wires at:
50C (650‎Ω) - 1.6mA
90C (‎167Ω) - 2.3mA
Min and Max currents measured at both extremes are 1.3mA and 2.7mA

DMM (Aneng AN8009) has no effect of the gauge display value vs set resistance at the potentiometer when I measure voltage or current.

MisterBill2: As for the ground question came up a few times, the gauge is connected to chassis ground (-) and 1 pin of the sensor is also connected to this ground at the gauge. The chassis plays no role between the sensor the gauge.

Bernard: I took a few pics of the tachometer. SMD LEDs might be the way, thanks.
The TO3P is for size reference. The gaps between the divisions are 5.5mm (0.216")
Putting square holes into the acrylic (backing/lightpipe) will be impossible. If I go square LEDs, the acrylic will get round holes and LEDs will pressfit in those. The dial face will get will get square holes somehow.

eT, Bernard, MisterBill2, dl324: Many of the terms such as gain, RR opamp I don't understand. If you have any part numbers in mind for various circuit ideas please let me know and I order them. I have ~ €50 for this project. If I don't have to buy a second sensor for €30, I think it's plenty. I can and will extend the budget if needed.
I have plenty of common value metal film (0.25W, 1%) resistors, plenty quality caps and a breadboard already. I never used the latter, but I'll figure it out.

Thank you

You will find a good description of an instrument amplifier IC in the "Analog Devices" website, and also many other places. An "RR" opamp means "rail to rail", which implies a device able to work correctly with input voltages for the whole range from the lower supply voltage through the most positive supply voltage. Since one of the input connections is at ground, that will matter a bit.

 

With +9V, R9 = 2k, a plot of V & temp shows a linear plot from 85 to 60 deg. & 60 to 40 deg.
LM3914 still tempting? Real measurements might show something different.

Hi Bernard

Here is a schematic update for review.
1. I changed the connection from the comparators to the LEDs. I think they need to be off until the signal is below the reference.
2. I've added a little overvoltage and reverse voltage protection.
3. I've shown a couple of opamps (Dual LMV841) for signal conditioning. I'll change this if someone prefers an instrumentation amp. Just let me know the choice..
4. Added an LM7809 regulator.
5. The Gauge current generator is a guess. I'm not sure what is really there.
6. Added two more comparators for ten steps.
Let me know if you need anything changed..

I've simulated the circuit and it seems to work.

eT

 

Are you illuminating both oil temp. & RPM ? Are both gauges the same diameter ?
If using LM3914 , there is no need for additional buffering of input, it's built in.
Is there space enough to slide a piece of .005 in. red diffusion #120, Roscolux film between face & plastic backing ?

Post #1 : All LEDs on until temp. reaches 40 deg. C then they fall out one by one as temp. rises, or something similar.

Any choice yet on LM3914 or home brew bar graph ?

 

Guys, this schematic looks AWESOME! I think I could build this. I need a bigger breadboard if I want a testrun first.

@ point no.1: All LEDs should be on @ and below 40C.

Bernard: I think I know what you are thinking, but I'll need high power LEDs to shine through at daytime and then when the LEDs went out, the numbers and divisons (above lets say 3.5k) would remain red.
But I could do the above without the red film maybe.

The oil temp gauge is a complely different aftermaket unit. It a 52mm in size. (Kind of like the size of my OE temp/fuel gauge below)

Just actually today I was experimenting with various colors to upgrade the look of my originally white/red instrument cluster.
What a coinsidence you mention it today.



I haven't decided if I went too far or not.
(The LED temp display on the right is also my creation, not OE)

Must sleep now, thanks again guys!

 

Post #1 : All LEDs on until temp. reaches 40 deg. C then they fall out one by one as temp. rises, or something similar.

Hi

Oh...OK. I got that backwards then...I have them all dark until temp reaches 40C
I'll have to fix the schematic...

eT

 

Guys, this schematic looks AWESOME! I think I could build this. I need a bigger breadboard if I want a testrun first.

@ point no.1: All LEDs should be on @ and below 40C.

Bernard: I think I know what you are thinking, but I'll need high power LEDs to shine through at daytime and then when the LEDs went out, the numbers and divisons (above lets say 3.5k) would remain red.
But I could do the above without the red film maybe.

The oil temp gauge is a complely different aftermaket unit. It a 52mm in size. (Kind of like the size of my OE temp/fuel gauge below)

Just actually today I was experimenting with various colors to upgrade the look of my originally white/red instrument cluster.
What a coinsidence you mention it today.

View attachment 194208

I haven't decided if I went too far or not.
(The LED temp display on the right is also my creation, not OE)

Must sleep now, thanks again guys!

The reason for using 8 LEDs and 8 comparators is that each LM339 is a four comparator IC. So that gives you a small package, just 2 14 lead IC devices.

 

Are you illuminating both oil temp. & RPM ? Are both gauges the same diameter ?
If using LM3914 , there is no need for additional buffering of input, it's built in.
Is there space enough to slide a piece of .005 in. red diffusion #120, Roscolux film between face & plastic backing ?

Post #1 : All LEDs on until temp. reaches 40 deg. C then they fall out one by one as temp. rises, or something similar.

Any choice yet on LM3914 or home brew bar graph ?

OK....corrected the schematic.
All LEDs on steady below 40C and go dark one at a time starting at 40C.

eT

 

Bernard: I think I know what you are thinking, but I'll need high power LEDs to shine through at daytime and then when the

Hello,

You need to determine which LED's you'll be using because that's important information for the driver design.
Like was mentioned earlier, may need to add transistors, or something else, to boost the LM339 outputs.
Likewise, the LM3914 can output 30mA per LED max.

eT

 

Hi eT,

I decided, I'm not going high brightness ones. It might cause a messier look (light scatter) and I would also need a night mode as it would be too bright when I drive/start the car at night.
I go with the original idea. Square holes, normal LEDs
Here are the ones available to me: Full datasheets are one click away behind the links

https://ie.farnell.com/kingbright/l-1553srdt/led-square-ultra-red/dp/1142622

https://ie.farnell.com/kingbright/l-1553idt/led-square-red/dp/1142621

https://ie.farnell.com/multicomp/mcl293srd/led-5mmx5mm-150-super-red/dp/1581158

https://ie.farnell.com/multicomp/mcl293pd/led-5mmx5mm-150-hi-red/dp/1581159

Few questions about your/Bernards design:
D2 Zener: I go 18V as suggested, but what wattage should I choose?
Ceramics: I found only SMD ones at 16-25V range, I guess I can go 50V ones which are leaded (?)
R20 20k pot: Do I need multiturn there or just a single turn?
P1 - P10: Are these still 20k multiturn ones as in Bernards original design?
R1 - R10 LED current limiting: This might change depending of which LED you choose form above. Is that correct?

Thank you

 

With the circuit shown in posr #75 it would be simple to supply the LEDs separately and provide a dimming function based on the vehicles dash lights source voltage, which I presume is the source of dimming. That is a very common function provided on add-on equipment for the automotive market. Setting the dimming to match the rest of the displays may be tedious but certainly it could be done. So there is another option.

 

Few questions about your/Bernards design:

It's Bernards design...I just added some minor stuff.

D2 Zener: I go 18V as suggested, but what wattage should I choose?

I'd recommend using a TVS Bi-Diode instead (SMCJ20C, 20V, Bi-direct). But if Zener, go with 20v or 18v, 1Watt.

Ceramics: I found only SMD ones at 16-25V range, I guess I can go 50V ones which are leaded (?)

16-25v SMD is fine.

R20 20k pot: Do I need multiturn there or just a single turn?

multiturn trimpot

P1 - P10: Are these still 20k multiturn ones as in Bernards original design?

I think Bernard recommended 2K. They are multiturn.
I breadboarded one comparator as a test with a multiturn 2K trimpot and worked fine.

R1 - R10 LED current limiting: This might change depending of which LED you choose form above. Is that correct?

That's correct. Transistors will have to be added to support greater than 10mA

However, lets wait for confirmation of the above from @Bernard .

@MisterBill2 ....Feel free to comment MrBill.


eT

 

It's Bernards design...I just added some minor stuff.



I'd recommend using a TVS Bi-Diode instead (SMCJ20C, 20V, Bi-direct). But if Zener, go with 20v or 18v, 1Watt.



16-25v SMD is fine.



multiturn trimpot



I think Bernard recommended 2K. They are multiturn.
I breadboarded one comparator as a test with a multiturn 2K trimpot and worked fine.



That's correct. Transistors will have to be added to support greater than 10mA

However, lets wait for confirmation of the above from @Bernard .

@MisterBill2 ....Feel free to comment MrBill.


eT

I do have two comments, in fact. If you use the circuit as shown, I suggest using 20K pots for one reason, which is that with 10 2K resistances in parallel yjay presents a 200 ohm load to the regulator, meaning there is more power dissipated and more heat. So 20 K pots will present a 2K load. The second comment is that since all of the setpoints are in a rising voltage mode, you may be able to get away with putting all of the 2K pots in series, which reduces the span of each one by a factor of ten. That would make setting easier, except that you would need to add a series resistance tp each end of the string, because the entire range is only a small part of 12 volts, or 9 volts.
OOPS. Cancel that thought.
BUT you could use a different, lower voltage, regulator for the supply to the pots and make adjusting them easier.
Good thing that I caught that goof!