🚀 go-pugleaf

Over the Holidays I built a on-board battery monitor, similar
to the "Go-Light" available from ZZ enterprises but I believe this
to be better, and costs less.  The schematic was published in an 
RC helicopter magazine a while back, a fellow netter told me about 
it.  It works great and I plan to put one in all my planes.   
I'm posting the schematic for all of you that may be interested, 
I purchased all the required parts for a total of $6.30.

The unit has 6 leds: three green, two yellow, one red and has an 
adjustable potentiometer that allows you to set the voltage
at which the red led lights up.  I set mine to illuminate the red
led at 4.75 volts.  Whats especially nice about it is that it shows
you HOW MUCH the voltage drops when the servos are actuated, as well
as the current voltage.  For example, when the batteries are fully
charged, the topmost green led is illuminated, but when you start
actuating the servos, you'll illuminate the second or third green
led as the voltage gets lowered by the immediate drain.  After flying
a while, the second green led will be illuminated when the servos are
idle,but the third green led and first yellow led get illuminated 
when the servos are actuated.  You never have to guess the voltage
of your batteries, and you have much more information than a simple
"green for yes, red for no" device like the "Go-Light".

I'm sold on it.

Mark.

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Battery Monitor Schematic
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The unit is based on a LM3914 in a 18 pin package.

Pin
1	n/c
2	gnd
3	v+
4 	39K res to gnd
5	wiper of 1K or 2K 10 turn trim pot
6 	to pin 7
7	to pin 6 and R1 to pin 8
8	R1 to pin 7 and R2 to gnd
9	jumper to v+ for bar mode,open for dot mode
10	green LED cathode, anode to V+
11	green LED cathode, anode to V+
12	green LED cathode, anode to V+
13	yellow LED cathode, anode to V+
14	yellow LED cathode, anode to V+
15	red LED cathode , anode to V+
16-18 n/c

V+ to C1 (2.2uf tant) to ground.

The trim pot is connected between v+ and gnd (a voltage divider)
V+ connects to you rx system battery + and gnd to -.  Set the trim
pot to illuminate the red led at the voltage you believe to be
"unacceptable".  I used 4.75 volts.

Parts List:
-----------

1 - LM3914(National) LED Display Driver			$2.00
1 - 2.2uf tant cap					  .50
1 - 820 ohm res. 					  .15
1 - 220 ohm res. 					  .15
1 - 39kohm res.						  .15
1 - 1k or 2k 10 turn pot.				 1.50 
3 - Green LEDs 						  .30
2 - Yellow LEDs 				          .20
1 - Red LED (2ma LED for low current app)		  .10
1 - Radio Shack blank pc board				 1.25
                                                       -------
						Total:  $6.30