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lm3914 20 led voltmeter

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smilem

Member
Hi, I'm struggling to make 20 led lm3914 voltmeter.

Voltage range from 0V - 12V, adjustable with variable resistors.

I looked at **broken link removed**
But simulation does not work.
 

smilem

Member
I have put together this schematic (lm3914 dot mode) that works (in simulation).

Meas1 - this is the voltage that will be measured 0-12V
PSU1 - this is the lm3914 circuit power supply 12V

see attachment for schematic diagram.

I would like to:

1. add lower scale limit Potentiometer (my intended range 0-12V)
2. add upper scale limit Potentiometer (upper limit is ~12V)
3. add LED brightness Potentiometer

Thank you for your time
 

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smilem

Member
I found this schematic of 10 Led car voltmeter with adjustable lower and top voltage limits.
**broken link removed**

I tried to make 20 led version, but I have a problem led 10 stays always on if voltage is above it's limit. In bar mode you can't notice it but it's clear in dot mode.

I tried to find the error to no avail. Please see attachment.
 

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  • 5v-25v.png
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audioguru

Well-Known Member
Most Helpful Member
I tried to make 20 led version, but I have a problem led 10 stays always on if voltage is above it's limit. In bar mode you can't notice it but it's clear in dot mode.

I tried to find the error to no avail. Please see attachment.
Your very-hard-to-read negative schematic that is covered with chicken-pox dots is different from the schematic shown in the datasheet:
 

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  • LM3914 cascaded.PNG
    LM3914 cascaded.PNG
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smilem

Member
I changed the schematic like your image shows.
Please see attached image, for dot and bar modes.

In dot mode leds 10 and 20 do not work
In bar mode leds 11 and 19 do not work
 

Attachments

  • car bargraph 12-15-circuit-error2.png
    car bargraph 12-15-circuit-error2.png
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audioguru

Well-Known Member
Most Helpful Member
Thanks for turning off the chicken-pox dots.
But it is difficult to see details in the negative schematic. Pin numbers are not shown.

In the bar-mode, outputs Q1 and Q9 of IC2 are shorted to the positive supply.
 

smilem

Member
Thanks for turning off the chicken-pox dots.
But it is difficult to see details in the negative schematic. Pin numbers are not shown.

I have added pin numbers by hand and update the above schematic.

In the bar-mode, outputs Q1 and Q9 of IC2 are shorted to the positive supply.

Do you mean the connections are not required between IC2 pins 9 and 11; IC2 pin 1 IC1 pin 9 ?
 
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audioguru

Well-Known Member
Most Helpful Member
I have added pin numbers by hand and update the above schematic.
Thanks, but it is still a negative pic. It should have dark lines on a white background.

Do you mean the connections are not required between IC2 pins 9 and 11; IC2 pin 1 IC1 pin 9 ?
The datasheet shows how to do it. In the BAR mode, you are shorting pin11 to the positive supply so its LED will never light.
The second LM3914 has its pin9 connected to its pin11 (but not to the positive supply) only in the DOT mode. Then pin11 has a 20k resistor to the positive supply so that pin9 is high when the LED is turned off.
 

smilem

Member
Well I'm trying to make not bar but dot mode here. How can I short second LM3914 pin9 to pin 11 not to positive supply if leds are on a positive supply side? You can see that because wires are colored red?

The 20k resistor is connected as data sheet shows, or did I miss something and connected it wrong?
Can you draw wires on my schematic to make it clear?
 

smilem

Member
I have made another schematic more easy to read, but still same problem with led10.
20k resistor is connected to 1st LM3914 as shown in datasheet diagram.
LM3914 IC1 mode pin 9 connected to LM3914 IC2 pin1 as shown in datasheet diagram, then a wire goes to led 11.

The led 10 is extinguished as data sheet said, but now how to turn it back on?
 

Attachments

  • bargraph dot mode.png
    bargraph dot mode.png
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