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

How to design, prototype and test a two cell 18650 Lithium Ion battery pack level gauge using the classic LM3914 dot/bargraph display driver chip.
A favorite from Dave's youth!
Dave gives you all you need to know to implement a simple expanded scale voltmeter with the LM3914, without adjustment pots to tweak.
This one works from 6V to 8.4V - the usable capacity of a two 2 cell 4.2V Li-Ion batttery pack.

Category:

Science & Technology

Tags:

• lm3914
• chip
• circuit
• classic
• bar
• graph
• dot
• project
• design
• electronics
• breadboard
• resistor
• multimeter
• measurement
• datasheet
• lithium
• ion
• battery
• pack
• gauge
• level
• led
• display
• 18650
• cell
• capacity
• parametric
• 4.2V
• 4.1V
• 8.4V
• 8.2V
• expanded
• scale
• voltameter
• LM3915
• LM3916

[Erny1389]

Dave, what about current, which goes through 1k resistor divider network and comes through Rlo out and changes IADJ value?

[EEVblog]

@Erny1389 That's in parallel with the external resistor R1, so it is taken into account. There is no extra current that flows out of it, so no additional error term to worry about.

[brunotag]

I've got a question.

How did you power the circuit? With the "batteries" themselves or with a separate source?

[EEVblog]

@brunotag I mentioned that at the beginning, using a variable lab power supply.

[shanearnfield]

Ah, I didn't realise it would become a challenge, but looking a bit further I have found a brand new LM3914N with a date-stamp of "8124". I also found a 74C926N with "8112". In 1981 I had not long obtained my Technicians Trade Certificate and remember I was fiddling with a number of LED projects... Oh it now seems so long ago!!

By the way, I love your video's. I look forward to seeing them and really enjoyed this one in particular.

Shane.

[EEVblog]

@shanearnfield We have a new leader! Can anyone beat 1981?

[mageepaddy]

More circuit stuff like this Dave please :)

[NIKOSGEOR]

WE WANT MORE LIKE THIS.... SIMPLE OLD SCHOOL ELECTRONIC CIRCUITS!!! 

[raphasanches]

Man, wonderful job! Congratulations! And, please, keep doing it!

[Kalkaekie]

Very interesting !! Enjoyed it.

[WhiterockFTP]

Is there a smaller chip for 4Peds

[FullWaveElectronics]

This is great!

[GiorgioCapocasa]

That's just beautiful :D

[daafies2]

what happens at 2V in dot mode?

[sismancocuk]

thanks a lot for the great video.

[axel1973w]

Is there an easy and practical way to "determine" unlabeled, unsoldered unknown diodes? Some way to find out their original parts name maybe if not printed on the casing?

[mrsestherhouse]

thanks for another great video Dave, i learned alot :)