LM3914 - question

[caslor]

Nice .. so as i have made this one circuit working with Lm7806 i can supply with some voltage the lm3914...
as i saw from your lovely executable program for lm3914... 6v or 8v dont make any difference in the operation...
right?




10μf ? you are talking about the slosh filter schematic ? only there is these capacitors ...




1μ = 1μf = 1 micro farad ? ( i went to the electronic shop today and he stacked with that.. couldnt remember if it is right )




Question : in case we are not using the second opa in lm358 do we have to ground the ''non inverting input'' .
And bridge the op2 ''inverting input'' with the opa2 ''output'' ??
i read it somewhere in the net about this... and i am not sure what this will make better to the circuit

 

[ericgibbs]

Nice .. so as i have made this one circuit working with Lm7806 i can supply with some voltage the lm3914...
as i saw from your lovely executable program for lm3914... 6v or 8v dont make any difference in the operation...
right?




10μf ? you are talking about the slosh filter schematic ? only there is these capacitors ...




1μ = 1μf = 1 micro farad ? ( i went to the electronic shop today and he stacked with that.. couldnt remember if it is right )




Question : in case we are not using the second opa in lm358 do we have to ground the ''non inverting input'' .
And bridge the op2 ''inverting input'' with the opa2 ''output'' ??
i read it somewhere in the net about this... and i am not sure what this will make better to the circuit

hi,
This circuit is for a 7808 +8V supply also uses the 2nd half of the LM358 as buffer.

If you look at the LM3915 datasheet you will see that it specifies a 2.2uF or 10uF cap.

Ref the uF or µF thats micro-Farad

 

[caslor]

hi,
This circuit is for a 7808 +8V supply also uses the 2nd half of the LM358 as buffer.

Do we know the value of the buffer ?

If you look at the LM3915 datasheet you will see that it specifies a 2.2uF or 10uF cap.

Yes i saw it... in my circuit i havent place any one.. but as i am going to use longer cable for leds i will place them in my next build

Ref the uF or µF thats micro-Farad

i need more help about this... (as i told before..this is the broblem when you talk an other language )
in the schematics for capacitors used μ lets say 1μ that confuse me as i knew μf and pf as units..

 

[ericgibbs]

Do we know the value of the buffer ?

I dont understand.?
The buffer has unity gain with no inversion, so what goes in comes out

i need more help about this... (as i told before..this is the broblem when you talk an other language )
in the schematics for capacitors used μ lets say 1μ that confuse me as i knew μf and pf as units..

hi,
1p or 1pF = 1 pico-Farad
1u or 1µ is quick way of typing 1uF or 1µF = 1 micro-Farad
1n or 1nF = 1 nano-Farad

 

[caslor]

Thanks again for answering my question

 

[caslor]

Back again with some new General questions about Lm3914 function .

1) If we have select the Dot mode and for one ''reason'' we dont want to light on 3,4 leds.. Just the 2 first and the sixth last.. can we do it ?
we just not connect any leds there? or we connect a resistance the same amount of led has ?

2) Lets say that we have the tank floter with 5R-80R resistance... But we want to measure with Lm3914 from the range of 35 R- 80 R ... is that possible ? ( i think yes - changing the value of resistors,,, but i would like a confirmation )

3) If we had 2-3 circuits with lm3914 (each one for different measurements ) would be wise to place a fuse before the voltage supply?

 

[ericgibbs]

Back again with some new General questions about Lm3914 function .

1) If we have select the Dot mode and for one ''reason'' we dont want to light on 3,4 leds.. Just the 2 first and the sixth last.. can we do it ?
we just not connect any leds there? or we connect a resistance the same amount of led has ?

2) Lets say that we have the tank floter with 5R-80R resistance... But we want to measure with Lm3914 from the range of 35 R- 80 R ... is that possible ? ( i think yes - changing the value of resistors,,, but i would like a confirmation )

3) If we had 2-3 circuits with lm3914 (each one for different measurements ) would be wise to place a fuse before the voltage supply?

Hi,
You can just leave out any LED's you dont want.
I would always recommend a fuse on any vehicle project when connected/powered thru to the battery.

Ref Q2: if I understand you correctly, its possible to offset, below zero the 5R to 35R section voltage of the sensor.
Would you want the 10 LED's to display the tank value from 35R to 80R.?

 

[caslor]

You can just leave out any LED's you dont want.

Very nice to hear that

I would always recommend a fuse on any vehicle project when connected/powered thru to the battery.

Would you want the 10 LED's to display the tank value from 35R to 80R.?

that would be the idea... not that i needing that... just wanted to see if it was possible..

This is something that i will need when i decide to build the lm3914 circuit that will count oil temperature..
and i would like to display temperatures through Lm3914 from a certain value and up...

But for this i have to test first the temperature sender what resistance has in certain temperatures...

I would always recommend a fuse on any vehicle project when connected/powered thru to the battery.

something like this one?

 

[audioguru]

Surely only a single 5V regulator is enough because the max current of your circuits is much less than the 1A max of the regulator. It will need a heatsink. It needs input and output capacitors that are shown on its datasheet.

 

[ericgibbs]

Surely only a single 5V regulator is enough because the max current of your circuits is much less than the 1A max of the regulator. It will need a heatsink. It needs input and output capacitors that are shown on its datasheet.

hi agu,
I have already told the OP that only one Vreg is required, post #40.

Ref using a 7805, the OP is using LM358's and he requires a upper OPA swing of +5V, thats why a 7808 has been recommended.

 

[caslor]

so i have to use only one lm7808 for all this circuits..

Nice

audioguru i use the capacitors just i remove them only from the drawing .


what about the fuse number? should i use smaller ? bigger?

(The project is to make a board that will have 6 circuits using lm3914 ( tachometer, gazoline, oil temp., voltometer, oil presure, cylinder temp. )

 

[caslor]

This is my final schematic ... i think it will work

 

[ericgibbs]

This is my final schematic ... i think it will work

hi,
Looking better.
I would add some protection to the 7808 regulator and a little extra smoothing to the +8V.

With ref to R11 and R12 if you make R12 =1K and R11=3K6 this will set the LED current a couple of mA higher and make them slightly brighter

 

[caslor]

THANKS !!!


Questions now

If i supply 6 circuits with the same Lm7808 have to use an other capacitor ? (the one we use for extra smoothing +8v )

The same with the fuse...if we need bigger one than the 2A

In the shop with electronic parts when i asked they told me that there is not smaller than the 0 - 4,7 k
is that true? or there is any one with smaller range / more accurate ?

 

[ericgibbs]

THANKS !!!


Questions now

If i supply 6 circuits with the same Lm7808 have to use an other capacitor ? (the one we use for extra smoothing +8v )

The same with the fuse...if we need bigger one than the 2A

In the shop with electronic parts when i asked they told me that there is not smaller than the 0 - 4,7 k
is that true? or there is any one with smaller range / more accurate ?

hi,
One cap near the7808 will be OK, but dont forget the 2.2uF or 10uF required near to each LM3914.

The 7808 is rated at a max current of 1 amp, so providing the 6 circuits do not draw more than about 150mA each at anyone time, [which is highly unlikely] the 7808 should be OK.
When the full system is running, check the temperature of the 7808, if it running hot, fit a heat sink.

So the 2Amp fuse should be fine, locate it near to the battery.

I dont understand your question regarding the '0 4.7K'...????

 

[caslor]

The fuse box i am planing to place it on the board before the Lm7808 ( the board will be powered from the cars fuse box.. so working only when the key is turn on )


about the 0 - 4,7 k : When i went to the shop with electronic parts they told me that there is not a Trimpot with value smaller than 4,7 k

**broken link removed**


but now i check on the net and find out that there is Trimpot with 1k value

**broken link removed**



..

 

[ericgibbs]

hi,
You can get trim pots down to 100R, which part of the circuit are you fitting the 1K trim pot.?

BTW: the two trim pots in that lower image are surface mount.

 

[caslor]

I was thinking about the 2 resistors in the Lm3914 lets say that we have the R12 resistance in my drawing..
add a stable resistance of 1k and add in series with this one the trimpot with 1k so can adjust it for accurate reading

or with 100R trimer could simulate my tanks 5-80 R and didnt have to remove every time the floter from the tank to move it and see how the lm3914 reads

 

[caslor]

My friend one more question i forget to ask before.. it is more likely confirmation than a question..
in the resistance R8 95,5K (post #42) we can use any pair of resistors we want so that can tweak the gain/slope of the sensor opa output ?

lets say 82,5 K + 13K = 95,5 K or 75K + 20,5 K

Right ?


i download the Ltspice iv - program so make the same schematics and be easier to understand them
is there anywhere inside component for Lm7808 , Lm2917N 14 pin, Lm3914, Lm 358 ?

Very nice program even i dont know to work it... But makes drawing schematics more easy than Photoshop

 

[ericgibbs]

My friend one more question i forget to ask before.. it is more likely confirmation than a question..
in the resistance R8 95,5K (post #42) we can use any pair of resistors we want so that can tweak the gain/slope of the sensor opa output ?

lets say 82,5 K + 13K = 95,5 K or 75K + 20,5 K

Right ?


i download the Ltspice iv - program so make the same schematics and be easier to understand them
is there anywhere inside component for Lm7808 , Lm2917N 14 pin, Lm3914, Lm 358 ?

Very nice program even i dont know to work it... But makes drawing schematics more easy than Photoshop

Hi,
Any combination of fixed resistors can be used to make the final final.
On amplifiers I prefer to split the feedback resistor into a fixed and variable section.

Its useful to have some degree of adjustment on this type of project so that the output can be set exactly how you want it.

Ref LTS, I would sign up for the Yahoo LTspice users group, its free, they have most of the models you are asking about.
I have not seen a 2917 or 3914 model, but a web search may show one up.

Unzip this caslor1.zip , for the time being keep them in the same folder, create a folder under LTS and unzip the files into it.