Martin, this is an ancient post of yours, but I stumbled across it just now looking for info on LED brightness.
Do you still have the details for your bargraph at all? I'm keen to have a look at that myself.
I want to see under and over voltage on the dash the instant it happens, but I don't like the idea of having to interpret blinking rates of LED's, I just want a simple guage like your bargraph.
Attached is a bitmap with the layout, and following is the text description.
I have pictures somewhere of mine, if I can find them I'll post.
... then you can OOOH and AHHHH the cardboard and duct-tape housing
(Really ... I'm not kidding ...)
it uses a Radioshack 276-170 breadboard so you dont need to etch a board
******************************************************
This is the description for the Voltage Monitor.
The monitor is based on a pair of LM3914 Chips and a pair of
10-LED "bargraphs"
(like those sequential LED "power" displays that are on stereo amps and
tapedecks)
I used 2 of each for a 20 segment display, but you could use only 1 of
each for a 10 segment display or lots of each for an N-times-10 segment
display
The upper and lower endpoints of the displays can be adjusted to
indicate anywhere between about 8 and over 20 volts or so.
You can get the data-sheet for the LM3914 at
http://www.jameco.com/Jameco/Products/ProdDS/24230.pdf
The 3914 is pretty easy to use, and the monitor is more or less right
off the datasheet ...
The picture is the layout, and it is so simple, I didn't even draw a
real schematic.
it uses a Radioshack 276-170 breadboard so you dont need to etch a board
Jameco part#s are
300003CK 2 LM-3914
334529CK 2 LED Bar (Red)
334511CK 2 LED Bar (Green)(alternate to above ... pick your favorite color)
330798CK 1 10uf electrolytic
25523CK 3 .1uf ceramic chip (bypass)
41822CK 2 10K 15-TURN POT
41873CK 1 20K 15-TURN POT
Assorted resistors
an explanation of how it all works:
----------
The LED displays are at the top of the board.
Only the cathodes of the LEDs are soldered into the breadboard, where
they connect to the LM3914s.
The LED assemblys are then bent almost 90 degrees so that they can be
seen when the board is seen edge on from the bottom (see pictures)
This makes your display 1 inch high and 3 inches deep (and 3 inches wide)
All the anodes are then connected to a hookup wire which is connected to
V+ (see picture) (actually, I divided mine into 3 sections ...
electrically the same thing, but mechanically stronger)
Instead of bending the LEDs, you _COULD_ just solder the anodes directly
to the board at V+ (you would need to drill 3 holes), but then your
display would be 3 inches high and an inch deep (and 3 inches wide)
(I.E. it would not mount on the bike as well)
---
In the middle of the board are the 2 LM3914s and the associated
circuitry.
Each LM3914 has resistors connected to Ref-out and Ref-adj to set the
LED current and the voltage refrence.
(LM3914-1's Ref-out is not actually used, but is programed anyway so that
it roughly tracks LM3914-2's Ref-out)
Please note that the resistor values for LM3914-1 and LM3914-2 are
different.
(since those for LM3914-2 also account for the current drawn by the
internal divider chain)
There are also resistors connecting pins 9 and 11 of LM3914-1 to V+
which are required for proper daisy-chaining
---
On the bottom left corner are four 22k resistors.
(I think I may have changed these to 10k in the end, to make the LEDS a
bit brighter)
These connect ground to the cathode of four of the LEDs in order to
dimmly illuminate these LEDs at all times. The purpose of this is to
give a sense of edges of the display when it is dark outside. Kind of
like "background illumination". You could eliminate any or all of them
if you wish (or add more ...) The only requirement is not to connect to
LED 9 of the first 3914 or LED 1 on the second, since that would screw
up the daisy-chaining. When the 3914s illuminate one of these four LEDS,
they just add to the resistor's current, and swamp it. These LEDs are
shown in a lighter color in the layout for refrence. This idea is not
shown in the LM3914 datasheets
---
The caps are all just for bypass. A 10uf electrolytic and .1uf chip
where power comes on the board, and one more .1uf at each IC.
Thats probably way overkill, the first 2 are probably enough...
(and its possible that you could get away with no bypass anywhere at all)
But the caps are cheap, its recomended practice, and I'd rather not
track down oscillation problems because I tried to save 10 cents on a
cap.
---
On the far right are 3 multiturn pots. These set the high and low
settings for the Displays.
The rightmost pot is just a voltage divider between V+ and ground.
Its center terminal goes to the inputs of the LM3914s.
It is primarily used to set the voltage for LED 10 of the 2nd LM3914.
The other 2 pots do not have _MUCH_ influence on LED 10 of the 2nd LM3914.
The middle and left pots parallel the internal voltage dividers on
LM3914-2 and LM3914-1 respectively. The high side of the divider on
LM3914-2 is connected to the REF-out pin, and the low side of the
divider on LM3914-1 is connected to ground via a 10k resistor.
Thus the internal dividers and this 10k resistor form a 3 part voltage
divider which divides the ref-out voltage.
Since you can adjust the effective resistance of the internal dividers
with the parallel potentiometers, you can adjust the relative
proportions of the 3 part divider.
So you can adjust LED 10 of the 1st LM3914 (and LED 1 of the 2nd LM3914)
with the middle pot, and LED 1 of the 1st LM3914 with the left pot
Unfortunately, the other pots also interact with each of these settings,
so you have to iterate to get the settings correct...
You will need an adjustable powersupply to adjust the pots
It could be as simple as an LM317 (with a resistor and a pot)
http://www.jameco.com/Jameco/Products/ProdDS/23579.pdf
and two 9-volt batteries.
The setting procedure is as follows:
1) set the supply to the desired voltage for LED 10 on the 2nd LM3914
(for example 15 volts)
2) adjust the right pot till LED 10 on the 2nd LM3914 illuminates
3) set the supply to the desired voltage for LED 10 on the 1st LM3914
(for example 14 volts)
4) adjust the middle pot till LED 10 on the 1st LM3914 illuminates
5) set the supply to the desired voltage for LED 1 on the 1st LM3914
(for example 10 volts)
6) adjust the left pot till LED 1 on the 1st LM3914 illuminates
goto step 1 and repeat
(continue repeating until no more adjustments are needed in any step)
?
