LM3914 - question

caslor · Apr 25, 2010

THANKS !!!!!
Last night was ''play time'' i was changing some resistance values and watching the diagrams
But have a lot of time to achieve something by my self ....

so here i am again with a new question.

As i told you before the project is to have fuel gauge, oil temp, oil pressure with Lm3914

today was time to see about ''oil pressure''

the sending unit gives

20 R = 0 Bar
45 R = 0,5 Bar
60 R = 1 Bar
75 R = 1,5 Bar
95 R = 2 Bar
105 R = 2,5 Bar
125 R = 3 Bar
140 R = 3,5 Bar
160 R = 4 Bar
170 R = 4,5 BAR
180 R = 5 Bar

The problem is that changing R/Bar is not linear

i am not sure if just one lm3914 can display exactly 0,5 - 5 bar
2 lm3914 could work better to display values more accurate to the above readings ?

ericgibbs · Apr 25, 2010

caslor said:
THANKS !!!!!
Last night was ''play time'' i was changing some resistance values and watching the diagrams
But have a lot of time to achieve something by my self ....

so here i am again with a new question.

As i told you before the project is to have fuel gauge, oil temp, oil pressure with Lm3914

today was time to see about ''oil pressure''

the sending unit gives

20 R = 0 Bar
45 R = 0,5 Bar
60 R = 1 Bar
75 R = 1,5 Bar
95 R = 2 Bar
105 R = 2,5 Bar
125 R = 3 Bar
140 R = 3,5 Bar
160 R = 4 Bar
170 R = 4,5 BAR
180 R = 5 Bar

The problem is that changing R/Bar is not linear

i am not sure if just one lm3914 can display exactly 0,5 - 5 bar
2 lm3914 could work better to display values more accurate to the above readings ?

hi,
Its possible to roughly approximate the curve of the gauge by using opa's before the LM3914.
I'll take a look later on.

ericgibbs · Apr 25, 2010

hi,
This is a plot of the actual and best fit of the oil gauge resistance.
The 20R at 0Bar could be dropped, leaving 10 values to be displayed on a LM3914.

With the exception of the 5Bar value I would say its an acceptable fit.???

caslor · Apr 25, 2010

Wow !!

even 5 bar is acceptable

i check them with a bar gauge i have for this sender... i place the values of ''Best fit R'' and gauge shows exactly the bar for each R

it is amazing what a person can do if knows electronic theory

Thanks for one more time ericgibbs for all this time you spend from your time to help me

!!!

caslor · Apr 26, 2010

What kind of ''opa'' have to use to achive these readings?

ericgibbs · Apr 26, 2010

caslor said:
What kind of ''opa'' have to use to achive these readings?

hi,
Its virtually the same as the gas gauge.
I'll have a look at it, let you know.

ericgibbs · Apr 26, 2010

hi,
Look at this option.

ericgibbs · Apr 26, 2010

hi castor,
A 2nd option.

caslor · Apr 26, 2010

Thanks !!!!!

Yes it look like similar to the Gaz gauge.
one important difference is that in the second lm358 we supply the ''non inverting input'' with + from our 8v supply

in the ''OilGauge1.asc'' i am taking a warning message that a ''CA3140'' was not found... (i havent update yet the database of the ltc program ) i guess it has similar operation like the lm358 (you name it like this in the schematics )

and now one last thing and promise not to hear from me an other question for a while

This is something similar like the oil gauge but this time is measuring temperature..

the sender unit is ground it in the engine and sends the negative to the gauge as a signal through a internal resistance it has that changes as the temp rises

could you check this one also Pleaseeeeee

celcius - resistance
60 - 150 R
70 - 110 R
80 - 95 R
90 - 70 R
100 - 55 R
110 - 45 R
120 - 35 R
130 - 30 R
140 - 25 R

...

ericgibbs · Apr 26, 2010

hi,
You can easily delete and replace those ca3140 in the asc file and replace them with a LM358.

Ref the Tempr, when you say negative from the tempr sensor I guess you maen the 'slope' is going down from 150R to 25R as the tempr increases.

ericgibbs · Apr 26, 2010

hi,
Look at this option.

caslor · Apr 26, 2010

Yes the 'slope' is going down from 150R to 25R as the tempr increases.

The ''negative from the tempr sensor'' i refer that the sender is ground to the chassis like the other 2 examples we have looked until know (gazoline sender and oil pressure )

ericgibbs · Apr 26, 2010

caslor said:
Yes the 'slope' is going down from 150R to 25R as the tempr increases.

The ''negative from the tempr sensor'' i refer that the sender is ground to the chassis like the other 2 examples we have looked until know (gazoline sender and oil pressure )

hi,
That last circuit I posted should be OK.
Delete the CA3140 and replace with LM358 and you can try out ideas.

caslor · Apr 27, 2010

Hi

I play a little with the values of resistance but until know the best option is yours

Because i will start building my circuit i want one more explanation ..

in some schematics i find the word ''pot'' next to some resistances.. what is that? is a trimmerpot? adjustable resistance?

ericgibbs · Apr 27, 2010

caslor said:
Hi

I play a little with the values of resistance but until know the best option is yours

Because i will start building my circuit i want one more explanation ..

in some schematics i find the word ''pot'' next to some resistances.. what is that? is a trimmerpot? adjustable resistance?

hi,
Its an abbreviation of potentiometer ie: 'pot'
A potentiometer can be a variable resistor, trimming, preset..etc

caslor · Apr 27, 2010

Thanks

I think i find the best setup for oil-bar gauge

Based on schematic in post #67 i change the R4 from 100k to 90K and setting lm3914 to 0,48v step i think i get the best option..
specially for low bar pressure that most of the times engine runs

Thanks ericgibbs for all this (make the schematics, sharing them, lm3914 program, ltspice files and help me clear about some theoretic questions in electronics )

caslor · Apr 27, 2010

Hi

oups... here i am again for one more time asking for knowledge-help

i decide to use 2 lm3914 for temp guage to have more accurate readings .

i will not use all the leds just the ones that are close to the temps i want to display...

in the schematic what resistance should i place in order to have 0.25v step to the leds?

From program about lm3914 i saw that have to use R1= 1.18K and R2= 1.10K

But dont know if that can be used in this setup with 2lm3914

so here i am again asking your help

ericgibbs · Apr 27, 2010

caslor said:
Hi

oups... here i am again for one more time asking for knowledge-help

i decide to use 2 lm3914 for temp guage to have more accurate readings .

i will not use all the leds just the ones that are close to the temps i want to display...

in the schematic what resistance should i place in order to have 0.25v step to the leds?

From program about lm3914 i saw that have to use R1= 1.18K and R2= 1.10K

But dont know if that can be used in this setup with 2lm3914

so here i am again asking your help

hi,
I will have a look.
I think I am going to call you Oliver..

caslor · Apr 27, 2010

Thank ericgibbs !!!
i will wait

Ps : in the drawing i saw that i have left 14,8v power in pin 3 of lm
this is wrong... i will use the 8v i have for all my circuits

ericgibbs · Apr 28, 2010

caslor said:
Thank ericgibbs !!!
i will wait

Ps : in the drawing i saw that i have left 14,8v power in pin 3 of lm
this is wrong... i will use the 8v i have for all my circuits

hi Caslor,
Look at this diagram.
Note, the LM3914's do vary in one to another, so the pots I noted will be required if you are to get a smooth transition from #10 to #11 LED's and also to maintain equal brightness from bank#1 to bank#2.

LM3914 - question

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