LED Bargraph battery monitor part 2 · 9 October 08
OK. So You’d like to build a set of those neat little bargraph battery monitors!
Here’s the first article: part 1.
I’ll remind you once again of what you need.
For each meter you’ll need these components:
- LM3914 bargraph display IC
- 10 DIL LED bargraph display
- 10 uF electrolytic capacitor
- 100R resistor
- 1K resisitor
- 270R resistor
- 10K resistor
- 22K resistor (for the 6V version)
- 200R precision cermet trimmer
- 500R precision cermet trimmer
- IN4001 silicon rectifier diode or similar.
- a piece of stripboard 10 holes x 16 holes (strips run along the 16 hole side)
All resistors should ideally be 1% or 2% tolerance.
The electrolytic capacitor needs to be very small and short if you want to mount all the boards together as shown below.
I’m going to write this article as if you are building the bargraph for 6V batteries. If you are using 8V batteries, change the 22K resistor for a 33K resistor, If 12V then use a 56K resistor.
Please note that all components in these diagrams are shown from the bottom, as if you were looking through the board from the copper strip side.
1. Cut the stripboard into rectangles which are 10 tracks wide and 16 “holes” long.
2. Use a small drill bit or track face cutter to break the tracks like so:
Make absolutely sure you have cut all the way through the tracks. I blew a couple of LEDs in one of the modules by missing a hair’s breadth of track joining cut sections.
Please note: If you would like bar display mode instead of dot display mode (which I don’t recommend) then omit the second drilling on the bottom line.
3. solder in the links like this:
Links can be made from tinned wire without insulation such as cut off ends from resistors and diodes etc. Make sure the ends of the links do not protrude far through the board because you don’t want them to interfere with the next board if you are mounting them together.
4. insert the chip and verify that you have it in the right place and the right way around. Remember my diagrams are shown from the bottom. Once you have done this then carefully bend the chip pins toward the center line of the chip (like a dead spider) to retain it. I used the edge of the desk but it can scratch the desk. Don’t solder them yet.
5. You have a 10 LED DIL bargraph module a bit like your chip only it has ten pins per side rather than nine. One side will be anodes, one will be cathodes. Find the side with the cathodes and lay the ten pins against the ten track ends right next to where the chip is mounted. The circuit board should be between both sets of pins on the LED module and against the cathodes. There should just about be room for the pins beside the chip legs you haven’t soldered yet. Now solder the pins in place. Nine of them connect directly to the chip pins. The last one is just above the marked end of the chip.
Good. Well Done!.
Solder the rest of the chip pins in if you have not done so already. The picture shown has everything soldered but it does show the way the LED module is mounted on the end of the board.
6. Add the resistors now. I recommend the order to be 100R,22K,10K,1K and 270R then the two variable resistors, 200R and 500R. Remember we are looking from underneath here.
Things to note:
There isn’t going to be very much room: Maybe keep the 100R resistor a couple of mm off the board to as to be able to fit the 22K resistor in because one end of the 22K plugs in directly under the 100R resistor. Keep the 22K resistor close to the board because there need s to be room for a diode later. The 1k resistor need to be at least partially standing up as it’ mounting holes are too close otherwise. same goes for the 270R resistor which need s to be completely standing up (in a “u” shape with the resistor on one side and a length of lead on the other). It’ll also need to be pushed over a bit to reduce it’s height. The 270R resistor does something a bit sneaky here because of space. One of it’s leads emerges into one of the track cut-outs you made earlier. See the diagram above.
The 200R and 500R variable resistors are straightforward to mount. Note that they are staggered with respect to one another. Please bend the leads inwards over the tracks just like with the chiip to prevent them sticking too far below the board.
7. solder in the diode with the cathode (the painted end) towards the chip. This diode will prevent current from passing to the chip’s power supply if the monitor’s terminals are reversed.
8. get the small capacitor and bend it’s negative lead (normally next to the stripe) directly outward at the case. Bend the positive lead so that it follows the first lead but a couple of millimeters lower down further away from the case. The two leads should be parallel now and pointing away from the case to one side (the side with the stripe) Now poke the leads through the board as show in the diagram. The capacitor shoulld be lying down directly over the diagonal wire link. Trim the leads and solder it in.
9. As shown on the picture below: You see the 10 anodes on the LED module which are not soldered yet? OK. Bend the first and last pins down by a few degrees, maybe 20. Now fashion a bit of wire so that it sits against all the pins, under the 8 straight ones and over the two bent end ones. Leave a couple of centimetres free at the end near the notch on the chip. This need s to go through the board next to the Vcc (+) pin on the chip which is pin 3 it is the same track as the positive lead on the capacitor. Make sure everything is straight, Solder the wire up to the board then all of the LED module anode pins. It’s a bit fiddly.
10. The boards are connected by leads or pins on the top and bottom track of the board on the other end to the LED end i.e. close to the variable resistors. The positive track is the one which is closest to the adjusting screws on the variable resistors. It also leads to the diode. The negative track is the other one.
The positive track and the adjustments mark the “top” of the board i.e. the bargraph display starts from the bottom of the board closest to the the negative supply at lower voltages and finishes at the top of the board closest to the positive supply.
One mounting idea for attaching lots of these boards together is to attach short leads, half a centimeter to the tracks pointing back away from the board (I put mine through the board first)
Then the boards can all be soldered next to each other to a master boards which is also 10 “holes’ high. This keeps the spacing correct and your LED modules can be glued to each other with superglue to make a rigid multi display. Each individual element is exactly 1 inch high, 0.4 inches wide and 1.95 inches deep.
Have fun!
James May in the UK
James! This is brilliant.
So glad you posted the DIY at last because I’ve been telling everyone who will listen how incredibly useful your LED monitor is; I’ve pointed more than a few people to part 1 for the details.
It’s been an invaluable tool for initially weeding out the weak & dying floodies from the pack, and for protecting the longevity of the replacements & remainders.
For anyone with an older, less-than-perfectly-balanced pack, driving an EV without a monitor like this is akin to playing Russian roulette with the batteries.
cheers!
Darin
Would it be possible to get a parts number list from some place like mouser.com? The circuit looks simple enough to build, but picking parts always seems hard.
I can’t believe I don’t see anything like this on eBay…
hint, hint!
I’ve done a surface mount board layout for this in Eagle. I havent built it yet, but I’ll donate it.
How’s this?
Now, if we could go together and make up the boards – i’ll take 25 right off the top.
Bob
LED BAR/DOT GRAPH BATTERY CELL MONITOR
PART SOURCE PART NUMBER
LM3914 bargraph display IC Mouser 526-NTE1508
10 DIL LED bargraph display Mouser 604-DC10GWA
10 uF electrolytic capacitor Mouser 140-L10V10-RC
100R resistor Mouser 660-MFS1/4D52R1000F
1K resisitor Mouser 660-MF1/4DC1001F
270R resistor Mouser 660-MF1/4DCT52R2700F
10K resistor Mouser 660-MF1/4CCT52R1002F
22K resistor Mouser 660-MF1/4DC2202F
200R precision cermet trimmer Mouser 652-3006P-1-201-LF
500R precision cermet trimmer Mouser 652-3006P-1-501-LF
IN4001 silicon rectifier diode Mouser 621-1N4001
stripboard 10 holes x 16 holes Mouser
(strips run along the 16 hole side)
If produced for a group, a simple three position switch to toggle 6V, 8V, 12V, could be added to meet the needs of everyone.
Hi Everyone
Thank you very much for all the feedback. If somebody tries to make one these meters and had difficulty or if the instructions are hard to follow then I’ll update them as required.
Darin: Thanks for the product endorsement! (I sold 8 of these meters to Darin last year)
Danno: Maybe I’ll make some more of these, I haven’t decided yet. In the mean time, I’m sure somebody else can improve on this design.
Jon: If you send your stuff to me or to Jerry, we’ll post it up if you want to share it with everybody.
Bob: Thanks a lot for going to the trouble of looking up all those product numbers. Remember to change the 22K resistor to a 56K resistor for a 12V meter.
Nick: I’m not sure, I think it would be cheaper and easier just to supply two or three different resistors if you were providing a kit or just put in the right one if you’re making them to order.
To make sure you order the correct voltage divider resister:
22k for 6volt
33k for 8 volt
56k for 12volt
Simply substitute the correct value, 22 or 33 or 56 in the part number.
Great info. Thanks for sharing. I did not see, but how long does it take to assemble one of these, and approximately how much are the components? Then I will know if I should give this a go or not.
Cost?
My initial pricing using the mouser catalog runs about $465.00 plus shipping for 25 boards.
Based on the retail prices listed for the parts specified (all resistors are 1%, there may be cheaper options) the total would be about $18.75 for each element.
BUT: the LM3914 lists for 9.14 each at Mouser then you add shipping.
I paid 3.54 each with shipping on ebay. If cost is an issue, look around and you can find some pretty good prices.
Bob
I can get the Led driver (070017-51 3$) bargraph (170159-1 2$) and trim pots (1$) locally at www.Addison-Electronics.com
The other components are pennies each so we’re looking at about 10$/ea.
They ship internationally.
It took me between twenty minutes and half an hour to assemble these when I got in a rhythm. Sometimes they didn’t work first time because of a short or a dry joint and took a little longer. It takes another 5 – 10 minuted to calibrate them using a variable voltage supply.
Just a thought – I haven’t checked your parts lists but make sure that the variable resistors are those long worm screw type so that they fit the design of the board and that the capacitor is a miniature one. Mine are around 4mm in diameter and 6mm high. That way you’ll be able to stack the boards with no interference.
James,
All good cautions.
Yes, I think careful shopping can produce these boards for 9-10 dollars cost of parts.
Regarding the parts listed from Mousers (they are available at dozens of places, I just happened to have a Mouser catalog handy):
the caps listed are stated to be 3×7mm – should be small enough.
the trim pots are high precision 10 turn “long” style as pictured above
the resisters are all 1% tolerance, and 1/4 watt in size
Are there any other things to watch for?
I’m looking at stripbpard that comes in 5 inches by about 6 inches – thinking I can get 4 or 6 pieces out of each – does this sound workable? (unless a nice mask for etching our own becomes available.)
Thanks,
Bob
I would think that a Eagle design could be sent here:
http://www.batchpcb.com/
and have the boards made up that way. Little less fuss, and the soldering becomes easier.
It would be even cooler if we could come up with an isolated version. That way all the high and low references of the LM3914s could be tied together. Then you could use one set of pots to control all the upper and lower limits of all the LEDs. Also it would be nice not to have the high pack voltage inside the passenger compartment. Any ideas?
For the initial design, I’ve come up with pricing at Newark.com.
~95CND$+shipping+taxes
Parts list for 12× 12V:
58K2341 12
97M6266 12
58K3919 12
58K3945 12
01F8182 12
01F8183 12
33K4103 12
18C8911 12
58K3886 12
58K3885 12
38K4677 12
Paste that into their “Quick Paste” window in the shopping cart area. Adjust the 58K3945 part for 6V or 8V as needed. Use the voucher “SAVE5C” to knock 5% off the total, and voila!
So that’s less than 10$ a piece delivered next day UPS.
My order has been placed, I just have to pick up the stripboards, some soldering supplies and a used bench power supply — any excuse for some new tools!
-Nick
Couldn’t you have gotten your strip board from them too?
Part#: 05M1088 $10.95
38 strips X 84 holes
You should be able to get 15 boards from that, or 10 to 12 boards and the back board maybe.
http://www.farnell.com/datasheets/79883.pdf
You can get the
LM3914 bargraph display IC
from Jameco Electronics
Part# 24230 @ $2.39 ea.
Min. order is 1.
From what I have seen, Mouser would be a good place to buy the other parts.
here is a cool idea too.
http://autospeed.com/cms/A_110623/article.html
I can’t help but liking ideas that are on the cheep so read all the way down.
Update: I ordered parts from three sources. Two of them delivered today. I have in hand everything for my 25 boards except the LM3914’s. I’m sure they will be here before I get all 25 boards cut to size and the strips routed out. The good news: I’m on my way and haven’t yet made a single mistake.
Warning! I have just seen a slight mistake on my diagrams. The chip is wider than shown on the diagrams. It’s pins are four ‘holes’ apart rather than three. This means that the left hand row of pins are one hole further left than shown, that is, one hole closer to the LED array. I’ll see if I can fix the diagrams in the next few days.
James,
I saw that – the photo of the finished board at the top of this page reflects the difference – just be sure to place the LM3914 one row towards the front and not towards the back.
We could always make the boards a whole .1” longer, but I don’t see a problem – just be sure to put the chip in the correct verticle columns of holes.
Yes, there’s no need to make the boards longer. You can fit everything in this way, it’s just a diagram mistake.
I think it is a good idea to fit fuses close to the batteries on all the wires leading to the meters.
Isolation: It would be better to have meters in the car electrically isolated from the batteries to reduce shock hazard. I don’t it can practically be done with this circuit unless anyone else has ideas.
The Paktrakr is isolated, which is an advantage. It is not quite as resposive or easy to read as these meters in my opinion. Maybe someone could design a PIC based circuit to drive LED bargraph array based on the output of a Paktrakr remote. They output serial ascii values in a CSV stream I believe. Doing this would reduce high voltage wiring.
LM3914 is $1.75 at AllElectronics.com http://www.allelectronics.com/index.php?page=search&search_query=lm3914
The LEDs are $1.50 in quantity greater than 10
http://www.allelectronics.com/index.php?type=&page=search&action=&id=&skip_redirect_suffix=&view_id=7affabb69887942aaf4581ebe3f6f19841e6af10&search_query=bargraph
I used these boards which are $0.75 http://www.allelectronics.com/make-a-store/item/PC-1/SOLDERABLE-PERF-BOARD/-/1.html
Another important idea is fusing and wire size. Each LED bargraph monitor draws very little current so the wire doesn’t have to be a heavy gauge. What you do have to consider is the insulation of the wire. True each wire is handling about 12 volts but you still have to consider that the entire pack voltage may be on two adjacent wires in your cable.
Fusing is another consideration and you should keep in mind the entire pack voltage when choosing an appropriate fuse voltage.
I’m not sure if this has been mentined but… Another consideration is the calibration of all the monitors and I propose that when calibrating the upper and lower voltage values you utilize the fact that the LM3914 has a very small window of overlap that causes 2 adjacent LEDs to be on at the same time so as to avoid ever having no LED lit up. You can calibrate more accurately using this concept. ie with all the + sides connected together and all the – sides connected together, you apply a voltage that is in the middle of the value for the lowest and next lowest LED and adjust the calibration pots so both LEDs are on. Then you do the similar step for the 2 higher voltage LEDs. electricDeLorean.com
Hi Dave,
This is a very helpful contribution. Thank you.
In fact I was calibrating them at the exact point the bottom LED went out and at the exact point the top LED was lit alone and not overlapping with the second LED
Another note. The boards I used have mounting holes in the corners and I bought a length of 6-32 threaded Nylon rod and cut it into 4 pieces. These pass through the holes for mounting. in between each board is a Nylon spacer, ?3/8” if I recall. I finally have it all working in the eLectric DeLorean. I have a photo of the finished product but not of the insides and boards yet.
Well done Dave. I feel honoured to have contributed in a small way to an eLectric DeLorean!
Hi Dave, thanks for the useful information. I have one question, how much would one of this LED Bargraph battery monitor cost? Can I get it off the selves?
They shouldn’t cost more than $10 each for the parts. I do not know of anyone selling these but the unit at http://autospeed.com/cms/A_110623/article.html as DanP above noted can be purchased.
I’ve just completed 3 of the 12 I need.
I have redone the component routing for a board without traces. Thanks to Dave for pics of his implementation, but given we didn’t quite have the same components, I had to move things around a bit. Here is the diagram.
http://docs.google.com/Doc?id=dhmzznh8_6g795t582
Very nicely done, Nick!
Nice! This meter is small, slick and convenient. But, if you have room behind your dashboard, you could mount a $3 digital multimeter (Chinese item sold at Harbor Freight in the U.S.) with lcd display.
However, it runs on a 9 volt battery, so you would have to keep changing that, or hook it up to your vehicle’s system with a resistor inline to drop the voltage. When the meter goes dead, you know you have less than 9 volts.
Maybe the programmable Sears Wood Carver could cut the copper strips then cut the individual panels from the main panel.
Fusing should be done both at the board and at the battery (cell).
On the board you can use a SINGLE strand of wire from a multi-stranded conducter (10ga for example).
At the battery, rather to the battery, not much works better or is cleaner than telephone wire. It’s so small that any short will melt the conductor long before the insulation.
PS: THANKS GUYS! This stuff is GREAT!
You can replace the Vishay trim pots with some much less expensive pots and shave another $2 from this.
The 01F8182 is $1.43 but the 05N1557 is just 0.44.
Similarly the 01F8183 is also $1.43 and the 05N1562 is 0.44. They’re the same specs.
Great little design. I watched the YouTube and this is JUST what I was looking for, a real time image. I don’t want to program a computer while I’m driving. But to get a real time visual indication of each battery while operating is the tits.
With the above substitutions, you should be under $8 in parts per battery.
Many thanks.
Reading about how this was used in the Forkenswift, it occurred to me that it would be handy if the meter could ‘remember’ the lowest voltage for each battery. Maybe an amber LED could be latched ‘on’ for any battery that dropped below the danger level while the go-pedal was pushed? It seems to me that this would help locate bad batteries without having to focus so much attention on the gauge.
I’ve been looking for a monitor like this.
I just hope I can get it together without damaging anything.
I’m confused about where the pos/neg from the battery attaches.