LM3914 - question

[audioguru]

A '69 VW Beetle?
Where on earth is one still alive? Mexico?
Was it never driven for the first 30 years?

 

[ericgibbs]

hi caslor,

This is one option for the fuel gauge, the output connects into a LM3914.

 

[caslor]

audioguru

i live in Greece.. Here we have a lot of vw beetles in the road...still running and in good shape..
i own 3 of them.. one 1961 convertible , one 1963 and one 1969
Beetles were produced for almost 50 years and were produced 21,529,464 cars

so there are many many beetles around the world still running and with many new parts available


ericgibbs

Thanks one more time for the help.. i will start build it from tomorrow , will post results for this one

 

[ericgibbs]

audioguru

i live in Greece.. Here we have a lot of vw beetles in the road...still running and in good shape..
i own 3 of them.. one 1961 convertible , one 1963 and one 1969
Beetles were produced for almost 50 years and were produced 21,529,464 cars

so there are many many beetles around the world still running and with many new parts available


ericgibbs

Thanks one more time for the help.. i will start build it from tomorrow , will post results for this one

hi,
Can I suggest that you combine the two threads you have running on this topic.

 

[caslor]

hi,
Can I suggest that you combine the two threads you have running on this topic.

? i have only one.. the other one belong to an other person... but i can copy and paste the issues refer to my questions from there

 

[ericgibbs]

? i have only one.. the other one belong to an other person... but i can copy and paste the issues refer to my questions from there

Woops, my mistake...No problem..

 

[caslor]

Here i am again... Back to this project

I am not sure if i have understand well the schematics but i try to build a circuit ( didnt work )

i built this one and didnt work with lm3914 ....

i used 4,2k instead of the 4,3k ericgibbs has in the schematic because i didnt have a 4,3k
the same with all the other resistors that dont much ericgibbs

but i think the 100k instead of the 82k and 18k was ok..

why we placed 2 resistors instead of only one with the right value ??


What do you think is wrong with this one and dont work ??


thanks

it is a LM358 ( i forget to write it when i was drawing the circuit )

 

[audioguru]

Your circuit is meaningless because it doesn't have an input.
Oh. Is the "tank" an LC tuned circuit or is it the sensor for a gas tank?

 

[caslor]

the input is from R (Tank )

my tank has inside a sensor (resistance that variables - full gives me 5 ohm and when the tank is empty gives 80 ohm )

so takes the Ground and give it throw the resistance to the Gauge ..

 

[ericgibbs]

the input is from R (Tank )

my tank has inside a sensor (resistance that variables - full gives me 5 ohm and when the tank is empty gives 80 ohm )

so takes the Ground and give it throw the resistance to the Gauge ..

hi,
I have re-run the sim using your values and I get this result.
When you say it does not work, in what way.???
What do you measure with a voltmeter at the junction of R1 and R2 also the output vo.???

 

[caslor]

Ηι
It was no volts
My mistake.. i start checking my circuit and i find out that hadnt connect the R7 to the 6V

but still not working as it should ...

- at the junction of R1 and R2 i have 5.91 volts
but in the output i get 4.66 volts what ever i do - move the floter resistance....

i check it with a 4,7 variable resistance - trimmer instead of the cars floter... i get the same voltage 4.66v out the output for 0 k - 4.7k


what may i have done wrong??

the c1,c2 1μ are 1 μf ? ( that is what i have placed in my circuit)

thanks again both for the interesting you saw to my project-problems

 

[ericgibbs]

Ηι
It was no volts
My mistake.. i start checking my circuit and i find out that hadnt connect the R7 to the 6V

but still not working as it should ...

- at the junction of R1 and R2 i have 5.91 volts
but in the output i get 4.66 volts what ever i do - move the floter resistance....

i check it with a 4,7 variable resistance - trimmer instead of the cars floter... i get the same voltage 4.66v out the output for 0 k - 4.7k


what may i have done wrong??

the c1,c2 1μ are 1 μf ? ( that is what i have placed in my circuit)

thanks again both for the interesting you saw to my project-problems

hi,
I would concentrate your tests on junction R1 and R2, a voltage of 5.9V its way over what I would expect, it will over drive the opa.
You should measure between about 40mV and 480mV at R1/2 depending on the floats position.

Disconnect the float sender from the junction of R1 and R2 and use an ohm meter to measure the senders resistance for different float positions, lets know.

EDIT:
You must have the senders 0V [case] connected to the 0V of the opa circuit.

Using a 4.7K variable will not give a meaningful test for a 5R to 80R sender resistance.!

 

[ericgibbs]

hi,
A quick check shows that you will get 5.9V at the junction of R1/2 if the sender 0V [case] is not connected to the OPA's battery 0V.!!!

 

[caslor]

This is how i connect it...

the floter/sender is ground to the tank and the tank to the car chassis .... ( is somethink that can not be changed )

 

[ericgibbs]

This is how i connect it...

the floter/sender is ground to the tank and the tank to the car chassis .... ( is somethink that can not be changed )

hi,
I can see no reason why its not working, when its connected as you have shown.

The fact that you measure 5.9V at the junction of R1 & R2 indicates that the 5~80R sender is not connected.???

As a test disconnect the sender from R1/R2 and measure the resistance of the sender to the chassis, let me know what you measure.

EDIT:
I am assuming that the GROUND symbol on the drawing indicates the car chassis.

 

[caslor]

Yes the first ground sympol is car chassis

from chassis to the floters cap (where it is gound to the tank) is 0.1 ohm
from the chassis to the output of the floter/sender is 28.9 ohms ( normal as it has some gazoline inside the tank )

the 5,9v is measured no maters if i have connect the sender...

so i must have assembly somewhere wrong the circuit ...

 

[caslor]

SUCCESS !!!!

Sorry for all this trouble !! as i was inspecting my circuit to check the connections... i saw that i had one bad-soldering to the R1 resistance where joins sender and R3

After fixing this... working absolutely fine thanks to yours affords


some extra info now ( hope not bored with my questions and mistakes )

if i had an other sender with 6 ohm - 75 ohm sender... witch resistors in the circuit have to change ?
(not care about the amount of the resistors just for understanding the circuit how it works)

if i want to have 3-4 seconds delay in the lm3914 display have to follow something like this schematic with both op amp lm358 connected ?

The schematic is from MikeMl from an other similar post

 

[ericgibbs]

SUCCESS !!!!

Sorry for all this trouble !! as i was inspecting my circuit to check the connections... i saw that i had one bad-soldering to the R1 resistance where joins sender and R3

After fixing this... working absolutely fine thanks to yours affords


some extra info now ( hope not bored with my questions and mistakes )

if i had an other sender with 6 ohm - 75 ohm sender... witch resistors in the circuit have to change ?
(not care about the amount of the resistors just for understanding the circuit how it works)

if i want to have 3-4 seconds delay in the lm3914 display have to follow something like this schematic with both op amp lm358 connected ?

The schematic is from MikeMl from an other similar post

hi,
A quick look at Mikes 'slosh filter' and sensor amp shows the signal is in the same sense as my version, so it should be OK to add the LM358 from point 'g' in the circuit.

I expect Mike will confirm this.

I am pleased to hear that its working OK , I am not bored when I get the answers to my questions that help me to figure out what you are doing.

Often we have to ask the same question over and over and then we may get an answer.

EDIT:
this for the 6R to 75R sender.

The reason for the 100K being in two sections is so that can tweak the gain/slope of the sensor opa output.

 

[caslor]

hi,
A quick look at Mikes 'slosh filter' and sensor amp shows the signal is in the same sense as my version, so it should be OK to add the LM358 from point 'g' in the circuit.

Nice to hear that

I expect Mike will confirm this.

I will wait his confirmation ... mike where are you?

Often we have to ask the same question over and over and then we may get an answer.

Yes some times is little hard to understand something that you know the basics and even harder when it has technical theory - words and not in your mother language

this for the 6R to 75R sender.

as i see we change the R6 resistance only... but i think because the very little diference between 75-80 R we could setup our leds working full scale from lm3914 resistors without change even this one R6...


Question : when we have 2 circuits like this project (one with lm358 and the other with lm3914) and we use the same voltage supply ( lets say 8v through lm7808) it is better to use one lm78xx for both circuits or use one lm78xx for each one ??

 

[ericgibbs]

Question : when we have 2 circuits like this project (one with lm358 and the other with lm3914) and we use the same voltage supply ( lets say 8v through lm7808) it is better to use one lm78xx for both circuits or use one lm78xx for each one ??

For circuits of that power dissipation a LM7808 will drive both.
Make sure you have the required smoothing caps on the regulator and a 10uF close to the LM7808.

BTW: if you power the sensor circuits from different voltage levels the circuit resistor values have to be changed.