Inverted LED bar temperature graph for Dynamic Redline indicator - LM3914/15/16(?)

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Hi Guys,
I'm new here. Not too new in electronics, but my skills and knowledge is fairly limited. It'll hopefully improve the more time I spend here.

I'm thinking to build in a dynamic redline indicator into my cars tachometer using LEDs like some BMWs have.
dynamic.JPG
The idea is that the redine goes higher and higher as the oil in the engine gets hotter.

I already have an aftermarket oil temperature gauge in my car, using an NTC sensor (40C ->925 Ohms --> 150C -> 32 Ohms), so I could tap into that or I could use a similar sensor only for this dynamic redline job.

I would like all (8 or 10) LEDs to be lit until the temp reaches 40C (105F) and than they would all turn off one by one as the temperature rises. I would like them all off at 75C (167F). I will work out the resistance values from the sensor for these temperatures.

Now finally the question :)
Could I build a circuit for this purpose using LM3914 or LM3915/16?

Please suggest some direction I could start with.
Soldering, measuring with DMM or reading schematics is not a problem, but building something complicated might be, so please suggest something simple.

Thank you kindly in advance,
Julius
 

eetech00

Joined Jun 8, 2013
1,715
Hi Guys,
I'm new here. Not too new in electronics, but my skills and knowledge is fairly limited. It'll hopefully improve the more time I spend here.

I'm thinking to build in a dynamic redline indicator into my cars tachometer using LEDs like some BMWs have.
View attachment 193581
The idea is that the redine goes higher and higher as the oil in the engine gets hotter.

I already have an aftermarket oil temperature gauge in my car, using an NTC sensor (40C ->925 Ohms --> 150C -> 32 Ohms), so I could tap into that or I could use a similar sensor only for this dynamic redline job.

I would like all (8 or 10) LEDs to be lit until the temp reaches 40C (105F) and than they would all turn off one by one as the temperature rises. I would like them all off at 75C (167F). I will work out the resistance values from the sensor for these temperatures.

Now finally the question :)
Could I build a circuit for this purpose using LM3914 or LM3915/16?

Please suggest some direction I could start with.
Soldering, measuring with DMM or reading schematics is not a problem, but building something complicated might be, so please suggest something simple.

Thank you kindly in advance,
Julius
Probably LM3914.
Do you have a part number for the NTC? I'd like to create a model...
Oh wait...its an oil temp gauge..

eT
 
Last edited:

Dodgydave

Joined Jun 22, 2012
8,469
Yes you can use a LM3914 , it has 10 outputs, so you need to set the Upper and Lower temperature limits on the comparator inputs, pin 4 and pin 6,, and input your temperature to pin 5, so for example 40C to 75C is 35 difference at 3.5C per led.
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Thank you for all the replies!

I'm not too sure how could I use the working principle of a VU meter as the circuit should be controlled by varying resistance rather than voltage. Also, I need this to be work inverted, so all LEDs ON by default.

Unfortunately, there is no part number for the NTC. All I know is 3 values for 3 temperature values.
104F (40C) = 925 ohms
194F (90C) = 163 ohms
302F (150C) = 32 ohms
This seems logaritmic to me.

The sensor: http://prosportgauges.com/temperature-sender.aspx

The gauge is stepper motor driven, thats all I know about it, but I wouldn't like to open it to extract some signal from it.

The gauge I have: https://rspec.co.uk/gauges-52mm-prosport-super-white-c-3_81/52mm-prosport-smoked-super-white-oil-pressure-gauge-bar-p-80.html

Dodgydave: So the LM3914 could be configured with pin 4 and 6 to have all outputs ON by default and they would go out one by one as the resistance drops (within set values) on pin 5?

Thanks again
 

eetech00

Joined Jun 8, 2013
1,715
Hello

The sensor will be used by the stepper gauge MCU to drive the movement. Configuring the LM3914 is the easy part. Somehow you will need to figure out how to interface the 3914 to the sensor without upsetting the signal to the gauge MCU.

eT
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Hi eT,

I could buy a second sensor only for this purpose, so thats not a problem. There are still empty spots on my sandwich plate where the pressure and temperature sensors are already mounted.
 

Dodgydave

Joined Jun 22, 2012
8,469
Thank you for all the replies!

I'm not too sure how could I use the working principle of a VU meter as the circuit should be controlled by varying resistance rather than voltage. Also, I need this to be work inverted, so all LEDs ON by default.

Unfortunately, there is no part number for the NTC. All I know is 3 values for 3 temperature values.
104F (40C) = 925 ohms
194F (90C) = 163 ohms
302F (150C) = 32 ohms
This seems logaritmic to me.

The sensor: http://prosportgauges.com/temperature-sender.aspx

The gauge is stepper motor driven, thats all I know about it, but I wouldn't like to open it to extract some signal from it.

The gauge I have: https://rspec.co.uk/gauges-52mm-prosport-super-white-c-3_81/52mm-prosport-smoked-super-white-oil-pressure-gauge-bar-p-80.html

Dodgydave: So the LM3914 could be configured with pin 4 and 6 to have all outputs ON by default and they would go out one by one as the resistance drops (within set values) on pin 5?

Thanks again
There are two ways to do it, use the Ntc voltage output as it decreases feeding it to pin 5, so the LEDs go out one by one, or use an OP amp with a fixed gain to give you the span you need for 40 to 75C on pin 5.
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Do you drive on ordinary roads at the redline? Why? Are you always racing somebody? Then please keep away from my roads where people drive normally and safely.
First of all, I am reducing my redline versus temperature so I'll go slower so you are safe!
This is a project for pleasure to create something unique, I'm not racing!
Finally, I'm 36, driving for 16 years and driven ~300.000kms without accident!
 

eetech00

Joined Jun 8, 2013
1,715
There are two ways to do it, use the Ntc voltage output as it decreases feeding it to pin 5, so the LEDs go out one by one, or use an OP amp with a fixed gain to give you the span you need for 40 to 75C on pin 5.
Hi

I don't think there is a "voltage output" from the NTC. I believe the gauge MCU energizes the sensor, measures, then performs some calculation to determine the temperature. I could be wrong though..

eT
 
My car has an automatic transmission and uses sensors and software to determine the best rpm for changing gears, usually much less than the redline to prevent wasting fuel and to prevent smoking my tires.
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Hi

I don't think there is a "voltage output" from the NTC. I believe the gauge MCU energizes the sensor, measures, then performs some calculation to determine the temperature. I could be wrong though..

eT
I think this NTC sensor is just a 2 wire bimetallic sensor, the same you would hook up to a DMM. I think the gauge monitors the resistance and converts it.

I was thinking of an LM35 for this purpose, but I couldn't place it reliably in the engine bay. Not only that, but I would like to read the actual oil temperature, not sticking a TO-92 on the engine block or somewhere.

I heard of Operational Amplifiers, but I'm afraid thats all I know about these.
If thats the only way, could anyone draw a simple wiring diagram?

Thanks
 

eetech00

Joined Jun 8, 2013
1,715
I think this NTC sensor is just a 2 wire bimetallic sensor, the same you would hook up to a DMM. I think the gauge monitors the resistance and converts it.

I was thinking of an LM35 for this purpose, but I couldn't place it reliably in the engine bay. Not only that, but I would like to read the actual oil temperature, not sticking a TO-92 on the engine block or somewhere.

I heard of Operational Amplifiers, but I'm afraid thats all I know about these.
If thats the only way, could anyone draw a simple wiring diagram?

Thanks
hi again

Basically, the opamp approach implies monitoring a know voltage/current source fed though the sensor. The Opamp would monitor the level across the NTC resistance. But it also implies a separate sensor. Maybe Dodgydave has a way to do this without adding a second sensor.

eT
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
My car has an automatic transmission and uses sensors and software to determine the best rpm for changing gears, usually much less than the redline to prevent wasting fuel and to prevent smoking my tires.
My car has a manual transmission. I got this car for 8 years now, starting with engine rebuild. I know this car from the 2nd compression piston ring to the exhaust holding bracket bolts. Changing oil every 7-8000kms (Castrol Edge or Valvoline Synpower) with the proper ACEA rating (A3/B4 not A5 or C3) What I mean with these boring sentences, that I am one of the last person in the country who needs an indicator showing how much to rev and load the engine if the oil is not at operating temperature.
Its only for fun and eyecandy for me :)
Love these little projects like most people here...(?)
 

Thread Starter

Juliuswws

Joined Dec 2, 2019
16
Did you deeply tint the windows and Indicator lights, lower the suspension and remove the muffler and catalytic also for "fun"?
Well, the answer is no, but it doesn't appear that you are actually reading what I'm writing! You can write for sure, I figured that much....However you haven't had a single useful sentence regarding the topic!
Please avoid me
 
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