EEVblog #204 – Designing a Li-Ion Battery Gauge with the LM3914

[BravoV]

Hey Dave, thanks for bringing out the classic ic, really love it, this definitely brings nostalgic moment !

Intermezzo, look here, my 3914 are younger than yours, circa 1992. 

[SgtRock]

Dear Dave:

--Great video. We beginners can pick up a lot of hands on knowledge from videos like this. I predict it will score many viewers.

"Ampère was the Newton of Electricity." James Clerk Maxwell

Best Regards
Clear Ether

[EEVblog]

Someone in  the Youtube comments is claiming 8348 vintage chips, that's the date to beat!

Dave.

[Psi]

lol, nice video.

I was just recommending the LM3914 to someone on here 2 days ago.


Found an old LM3915 (the log version) in my MISC ic box.
Looks like 1992 age

[EEVblog]

Someone on Youtube has upped the ante to "8112"

Dave.

[Lawsen]

National Semiconductor (Texas Instruments) LM3914, similar circuit is often found in the voltmeter/current meter displaying the brightness of microscope lamp house, LED bar graph like in the Olympus BH-2 and I am not sure about the Olympus BX series.  The newer microscopes did away with this LED bar graph denoting lamp house light bulb brightness.  My Olympus CX31RBSF does not have this LED bar graph lamp voltage.   We have seen some audio equipment with this LED audio volume voltmeter bar graph display in stereo recorders and amplifiers in the 1980s, past. 

The data sheet is available on the web or pdf, today.  Ten years ago, it was either on a text book, data sheet book from NSC (National Semiconductor Corporation), electronics instructions book like Don Lancaster, "TTL Cookbook."  TTL, transistor-transistor logic was very modern and people did earn good money implementing it around San Jose in the 1970s, the microcomputer and integrated circuit boom era.  I was too young then, but was fascinated reading about the new products, possibilities, and prosperity at the time.   

http://www.national.com/mpf/LM/LM3914.html#Overview

The battery tester instructions or bar graph voltmeters are in the book by Delton T. Horn, "Low Cost Test Equipment Projects You Can Build."

http://www.amazon.com/Low-Cost-Test-Equipment-Projects-Build/dp/0830641556

Thanks for showing the breadboard LM3914 set up, Dave Jones.  The wiring trace is simple, that I would like to etch my own board at home with mask tape and etch chemicals.  I will have to drill my own holes for the single sided through the hole components to populate the printed circuit board. 

[EEVblog]

Photo proof from Shane Arnfield, the current front runner for oldest LM3914.

Dave.

[Psi]

There's lots of cool things you can do with the lm3914/15

Like using the last led to switch from dot to bar mode.
So if the level gets too high all led light up as a warning.

[EEVblog]

There's lots of cool things you can do with the lm3914/15

I know, I've seen some weird uses over the years, it would be my pick for another chip contest!

Dave.

[vk6hdx]

Great video dave, as you said, you could have done it using a micro controller but where's the fun in that?  I love these little gem ic's.  I've been inspired to find a few of these chips and have a play around.

[Psi]

I've been inspired to find a few of these chips and have a play around.

Jaycar still sell them

[Zad]

Simple yet quite complicated. That would be an ideal problem to set prospective candidates for a junior development job. There are a couple of gotchas in there and plenty of questions to ask. I'm pleased to say that even Maplin here in the UK still carry these (which amazed me), even if they are £4:79. They are more interested in radio control helicopters, disco lights and batteries now.

[deephaven]

Simple yet quite complicated. That would be an ideal problem to set prospective candidates for a junior development job. There are a couple of gotchas in there and plenty of questions to ask. I'm pleased to say that even Maplin here in the UK still carry these (which amazed me), even if they are £4:79. They are more interested in radio control helicopters, disco lights and batteries now.

Farnell in the UK have got 1352 in stock and are selling them at £2 each or £1.18 each for 10 off 

[McMonster]

There's lots of cool things you can do with the lm3914/15

I know, I've seen some weird uses over the years, it would be my pick for another chip contest!

Dave.

Can you share some of them? Unconventional applications of parts is an interesting topic in itself. Specifically those parts designed to do very particular job.

[sdscotto]

I can't beat the contest for oldest, but I can show my age and fondness for the LM3914 (15 and 16) from the remaining parts in my inventory.   I got these when you could walk into the Mouser office in Santee, CA circa 1990:

[dimlow]

I'm confused Dave, shouldn't you be calculating the Led current in your circuit by using the total current through R1 and R2 to ground ? Not just R1, or am I missing something, please explain. Maybe this explains why your measured current  through the LED is not 2mA but closer to 3mA

[Alex]

Some modern devices like mobile phones contain much more sophisticated electronics yet their remaining battery indicator behaves like an LM3914 based design; first bar disappears quickly, then stuck in the middle bar for a long time and suddenly no battery left.

[Kozmyk]

Thanks Dave.
I really enjoyed following that process from start to finish.
Sneaky pitfalls especially.

Re your application - Low Voltage
Us RC nuts usually try to stay inside 80% usage with our LiPos.
The packs last longer that way and it keeps us well away from the drop off "cliff".
Low voltage alarms set between 3.3V and 3.6V do the trick.
We check that against mAH put back in at next charge; should be aprox 80% of nominal capacity.

Very low drain applications can actually be worse than high current for over-discharge as it can be easy to get right down to unhealthy cell voltages, and stay there; whereas in high current apps the cell voltage will likely bounce back up to a safe level once the load is off. 

[Kozmyk]

Some modern devices like mobile phones contain much more sophisticated electronics yet their remaining battery indicator behaves like an LM3914 based design; first bar disappears quickly, then stuck in the middle bar for a long time and suddenly no battery left.

You can expect a fairly rapid drop from the max 4.2V down to the nominal 3.7 then the slope should be fairly gentle until you reach the cliff.

What I learned about Li-ion/Li-Ion-Polymer cells, through RC modelling, has changed the way I work with such cells wherever I find them.
Whether in mobiles, laptops or cameras I try never to run them right down and I leave them at half charge if I'm going to store them without use for any length of time (more than a week).
I've taken to removing my laptop battery if I'm going to be running it on my desk.
I lose the UPS function but the pack lasts much longer.
There's a trade off in functionality there for sure so I guess it's a choice one has to make, full flexibility or pack life .

[EEVblog]

You can expect a fairly rapid drop from the max 4.2V down to the nominal 3.7 then the slope should be fairly gentle until you reach the cliff.

At high currents, yes, at low currents, no.

Dave.

[EEVblog]

I'm confused Dave, shouldn't you be calculating the Led current in your circuit by using the total current through R1 and R2 to ground ? Not just R1, or am I missing something, please explain. Maybe this explains why your measured current  through the LED is not 2mA but closer to 3mA

I thought about that, but that's not what the datasheet says. They are quite clear in saying that it is R1 only, without the error term, so perhaps the formula takes this into account. I don't know for sure, that would require further investigation and precise measurement. They don't explain how the internal circuit works, they just give you the formula and the graph.
There is a very large variation in the resistor divider, so that easily explains any discrepancy.
In either case, the exact LED current is not critical.

Dave.

[Kozmyk]

Having seen the uCurrent in action in the design process has made it a small object of desire for me now.

[Janne]

Nice blog entry. Old school analogue stuff still has it's place in many applications
I also ordered a couple of 3914's about 3 years ago. The date code in them puts them to year -87.. I don't remember where i got it but someone had been stockpiling 20 year old chips.

Link to a large image:
http://www.anotherpower.com/gallery/My-electonics-stuff/P1030608?full=1

The circuit is actually a wind power system dump controller. As the battery voltage increases, the LM3914 will switch on more heating loads, maxium 9 of them. It's been tuned so that the first element is turned on at 14.1V and the last one at 14.4V. I still have most faith toward analogue designs when they're running safety critical applications (as opposed to a micro controller based) 

Those 74LS14 inverting schmitt triggers are also of 70's vintage

edit. date code on them says 227X. Not so sure anymore if they're 70's or not.

[amspire]

I think the 74LS14 was made in 1972 27th week.  The X is a code for the assembly plant.

I think For a while in the 70's Texas were using singe digit numbers for years, before it struck them that it was not a great idea.

Also around then, they were manufacturing dies in the states and sending them out to places like El Salvidor for cheap assembly.

Texas only introduced the 74LS series in 1971, so having a 72 chip is pretty good.

Richard.

[mrwildbob]

Dave,

Thanx for the great vids.  Been watching you for quite some time.  I need some help with this project.  I would like to build a similar project to monitor an AGM battery for some ham radio projects.  My high voltage is 13.18 and low voltage is 11.27 giving a difference of 1.91V.  In the video you were able to use the reference voltage because it was close to 1.25V.  But what do you need to do differently if it does not come close to 1.25V?

Thanx a lot!

boB