LED Fuel Guage - someone verify my circuit please ?

[affinite]

The failure of the LED fuel guage display on my Moody 44 has prompted me to try and design a replacement.
My electronics knowledge is (very) rusty so Id appreciate an opinion as to wether the attached circuit might do the job for me.
Ive used an LM317 to get a stablized reference voltage for the sender and an LM319 to drive the LED's in my display.
Thanks in advance
Steve

 

[lw395]

I have not checked all the numbers, but from memory the vref of the 317 is 1.2V below v out, so either 5k is too big or 120 is too small.
It might be worth adding an inverse diode and a fuse to the supply, the diode shorts out short negative spikes on the supply rail, the fuse blows in the event of a long spike.
A diode across the 317 is also a good idea, t o prevent it being powered backwards during switch-off.
Some capacitors to help clean up the input and output of the 317 would be useful, the '12v' on a boat or car can very quite messy.

HTH?

 

[nigelmercier]

I've never used an LM3914, but you may have to play with the reference resistors R1 and R2 to get it to show full scale.

 

[affinite]

Yes thanks guys. I assumed that the reference voltage out of the LM317 wasnt critical provided that Full scalle is acheived by balancing R1 & R2 on the LM3914
Obviously never going to challenge the mighty YAPP Electronics Corporation

 

[mikefleetwood]

Assuming the LM3914 circuit is from the datasheet (it's a while since I've used one, so can't comment on the circuit), just two points:

1 - The LM317 will almost certainly need small capacitors on the input and output. This is not a matter of "smoothing", but to ensure stability - again, the datasheet will recommend values.

2 - The 180R resistor will have to be a relatively high power one - I would suggest 1W, most "hobby" resistors are about 0.25W, and likely to cook at low values of the sender resistor.