Dear All

The data sheet for the LM3914 display driver IC says supply voltage can be anything from 3v - 12v. Does this mean it would be ok to power the circuit from a 12v motorcycle battery?

I have tested it on a 3A bench power supply at 12v and it gets too hot to touch.

Thanks

Trevor

 

The supply voltage range is 3 - 25, so you can power the circuit from the battery. I remember that chip gets hot.
You can add a 7809 voltage regulator and some capacitors near the circuit (and not the battery).

 

Hi Eng1

Thanks for the reply. Actually, I did try a 7805 with a few caps and ran that off the 12v but then the 7805 gets extremely hot while the chip remains relatively cool.

If it's ok to run it directly off a 12v supply then I can cut down on a few components.

Trevor

 

the 7805 may get hot because ur droping 7V across it , also depending on the current demand

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That chip will get hot as it outputs the current for 10 LEDs and is only a DIP. I think there is usually an external resistor that sets the overall current, adjusting it could help.

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The output transistors in an LM3914 act as the current-limiting resistors for the LEDs so of course it gets too hot if you have a high supply voltage for the LEDs, the LEDs programmed for about 20mA each and the IC set to the BAR mode where many LEDs can be on at the same time. The LED outputs have current-regulation so just calculate the value of a power rersistor to add in series with the LED supply to handle the heat.

I put a 10 ohm/1W resistor in series with the LED supply in my project:
http://www.electronics-lab.com/proje...009/index.html

Attached Thumbnails

 

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Uncle $crooge

 

Audioguru,

Many thanks for the replies. I'm nearing completion of the fuel gauge project you helped me with some time ago and I'm just now trying to see what other functionality I can add while I'm at it.

One thing I'd like to have is a "low fuel" warning. The LM3914 has an alarm function where you can cause one LED out of the 10 and all those above it to flash when the appropriate input signal is applied.

Is there anyway to make this work the other way around ie the selected LED and all those below it to flash? Just an idea.

Thanks again.

By the way, very nice sound level projectand excellent write up. Very neat construction.

Trevor

 

Hi Trevor,
Thanks for the comments about my project.

The LM3914 and LM3915 don't light any LEDs at a low reading which would cause no voltage across a resistor feeding the LEDs, which can turn off a transistor which will make a low fuel alarm.

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Uncle $crooge

 

Audioguru

Thanks so much. I should have thought of that. I was fixated on trying to turn something ON instead of OFF.

Many thanks for the assistance and patience.

Trevor