LM3914 used for ammeter

[rapid]

I have been experimenting with an LM3914. I'd like to use this to detect the voltage across the 1/2 ohm resistor in the attached schematic. This resistor is used to bias the transistor that actuates current limiting in this power supply when current exceeds 1 Amp, that is, when the voltage drop becomes .5V or greater. Unfortunately, the resistor is not in the ground side of the circuit where I can "measure" it easily with the LM3914(by connecting it directly to pin 5). I'm considering putting another resistor in the ground side for this measurement. Is there another way to do this? I've looked through the archives and for other circuits on the 'net without finding anything similar.

Can someone explain the use of pin 8 when not grounded - as in most circuits?

 

[Roff]

Below is a way to translate the voltage to GND reference and to amplify it at the same time. The stuff on the left is yours - I just redrew it.
It sounds like you will need LM3914 help also. That will have to come another day if it's from me.
Pin 8 is well described on page 6 of the datasheet. You should read the datasheet thoroughly.

 

[lord saidus]

i was wondering if anyone has a spair or 2 of the 3m3914 i need 1or 2 for some automotive stuff and national wants like 10 bux for 2 of them just for shipping

 

[jbeng]

Try www.jameco.com Type "LM3914" in the search box.

Jeff

 

[audioguru]

My local electronic parts stores (not RadioCrap) have lots of LM3914 ICs.
One store buys surplus and liquidated parts and passes on the savings.