Help from cct designers please...

[Quigsworth]

Instead of using the standard fair from MV's re: LED V meters, I thought it might be kinda cool if there was a way to use LED's connected to progressively rated zeners to create a sort of "battery indicator" type thing???

semi-con cct's are waaay out of my league, am I out to lunch on this?

I'm aware of the Hextronik meter, I just wanted something a little more home brewed

 

[asdaq]

You can use a LM3914 to do that, but after getting all wired it might not wind up as small as you had hoped for.

 

[Quigsworth]

Thanks tons asdaq!, I just googled it and that's exactly what I've been looking for, but ya, I could see form factor being an issue...

 

[asdaq]

Sci did a nice indicator using it with a 10 LED bar that each .1v lights up another LED. There is a 2 digit display being used around now that is smaller, but I think it needs a driver. The 1s-6s isn't that large counting the actual display, but it does need some room in the case.

 

[TomCatt]

I think I saw a setup here somewhere with 4 or 5 LEDs to indicate battery charge level

 

[srolesen]

how about using 3 blue led's, each with different Vf, in series with a diode ?

 

[Sci]

The LM3914 setup isn't really that big. It looks large spread out on a breadboard, but, in reality, can be made pretty compact. The LEDs & resistors can be soldered directly to the chip. Also, you don't have to use 10 LEDs. You can use 3 RGB LEDs(&, in this case, fiber optics) with it. Sorry for the crappy vid quality.

Ignore all of the stuff on the back side of the bread board & this is far from being a finished project...

 

[Quigsworth]

You know, all the totally cool stuff I learn about on this forum...one of these days I'm gonna build a mod that has it all, sure, it's gonna need 14 batts and be the size of a microwave oven but it'll be wicked cool...thanks for all the replies! and thanks to you Sci for jumping in...

I did find this LM3914 battery level LED indicator module 4 arduino | eBay

I must have one of these...

 

[Ms. Creant]

I was thinking about this the other day. The circuit I was imagining was say 4 or 5 resistors of an arbitrary value, wired in series and at each of the resistor junctions is also the anode of an LED, with cathode to ground. Say you used 4 resistors, you would have 5 leds, one with no resistance, one with one resistor, 1 with 2 resistors and etc. the first led would light up at lowest voltage, led with 1 resistor would light at slightly higher voltage, and so on. Would that work? You might have to use a pot to test for the correct values and a variable power supply to supply the voltage to use while doing the testing.

This could be done for battery voltage or atty voltage, or both.

 

[srolesen]

Say you used 4 resistors, you would have 5 leds, one with no resistance, one with one resistor, 1 with 2 resistors and etc. the first led would light up at lowest voltage, led with 1 resistor would light at slightly higher voltage, and so on. Would that work?

no i'm sorry i do not think that would indicate battery level in a way that would be easy to read at all, each led would simply dim rather than turn off, and they would most likely dim in very similarly so you wouldnt be able to read the battery level from the intensity of the light
too bad tho i'd like a super small battery indicator like this too

 

[Ms. Creant]

I opened up one that I have for testing charging system battery level (solar 11.5 - 15.5V) It's kinda sorta like I thought except that the resistors aren't wired in series. The positive goes first through a variable resistor then through a fixed resistor, then to the first diode which is grounded straight to ground. Same for the other 5 diodes except their grounds go into a 16 pin IC.

 

[Sci]

Both pots could be replaced with resistors(just need the values for the voltages you want to display). Also, some of the wiring could be shortened/eliminated making this a fairly small unit.
The wires on the left side of the breadboard are not part of the circuit.

 

[srolesen]

looks good sci, but how about this for a small/simple voltage indicator?





sorry about picture quality idk how to make drawing online so i just take pic and upload it

 

[Sci]

I haven't really had much luck with zener diodes. Here's some good info on them.

I picked up some TL431's(adjustable shunt regulator) that I am going to try out. Here is a battery voltage monitor circuit using them. Google is loaded with circuits using them.

On a side note, as the voltage across an LED drops, it dims. Also, different colored LEDs have different voltage requirements. Take a look at this page about powering LEDs.

Hopefully some of that info can help you with your project. If the TL431s can be made to do what I want & be smaller than the LM3914, I'll use them. Otherwise, I'm sticking with the LM3914(what's controlling what I posted above).

One other thing, TinyCad is a great little free program for drawing/laying out circuits.

 

[Sci]

Here's a circuit, from here, using Zener diodes.

You'll have to change the Zener diodes to the ranges you want & maybe change the resistor values. I haven't had the chance to play with the circuit yet, so I don't know what the exact resistor values would be. The ones listed may work. Just remember to factor in the voltage drop across the LED & the resistor when figuring which zener to use for the different levels.

 

[srolesen]

awsome stuff sci, spent yesterday going through it, tyvm

i think you can skip zener diodes for 1 cell applications tho, use blue led's and buy them after how much forward voltage they drop (Vf) if each one has higher Vf you get the staircase effect (idk better english word for each led lighting up as voltage get's higher), if the scope is too low put in diode to drop a bit more voltage infront of circuit, then put in resistor for each led with no other purpose than to limit voltage through that led, i think it's simplest (smallest) monitor possible, but maybe missed something
again thanks for all the links much good stuff there!

 

[CraigHB]

One problem with making a Li-Ion battery indicator is the non linearity of the discharge curve. For my own mods, I use a table coded into a microcontroller to associate capacity levels with voltage levels. I had to build the table by discharging at a specific current for a specific time then taking a data point. It's very time consuming.

I don't know if this will help, but here's the table I use for my LiPo powered mods. It's not exactly the same as a LiCo or LiMN (IMR) cell, but I've found they're all pretty similar. These are the voltage readings when the cell is not loaded, in other words, not powering anything. You don't want to use measurments under load because in that case, battery voltage is relative to cell internal resistance and load current as well as state of charge.

This is for a 5000mAh LiPo cell at 3A discharge. Each data point is one minute. The times will not correlate to other cells, but the voltage levels and resulting capacity (far right) are similar.

0   4.19 - 100%
1   4.15
2   4.13
3   4.12
4   4.11
5   4.10
6   4.09
7   4.08
8   4.07
9   4.06
10  4.05 - 90%
11  4.04
12  4.03
13  4.02
14  4.01
15  4.00
16  3.99
17  3.98
18  3.97
19  3.96 - 80%
20  3.95
21  3.94
22  3.94
23  3.93
24  3.93
25  3.92
26  3.92
27  3.91
28  3.91 - 70%
29  3.90
30  3.90
31  3.89
32  3.89
33  3.88
34  3.88
35  3.87
36  3.87
37  3.86 - 60%
38  3.86
39  3.85
40  3.85
41  3.84
42  3.84
43  3.83
44  3.83
45  3.82
46  3.82 - 50%
47  3.81
48  3.81
49  3.80
50  3.80
51  3.79
52  3.79
53  3.78
54  3.78
55  3.77 - 40%
56  3.77
57  3.76
58  3.76
59  3.75
60  3.75
61  3.74
62  3.74
63  3.73
64  3.73 - 30%
65  3.73
66  3.72
67  3.72
68  3.72
69  3.71
70  3.71
71  3.71
72  3.71 
73  3.70 - 20%
74  3.70
75  3.70
76  3.69
77  3.69
78  3.68
79  3.68
80  3.67 
81  3.67 
82  3.66 - 10%
83  3.65 - 9
84  3.64 - 8
85  3.63 - 7
86  3.62 - 6
87  3.61 - 5
88  3.60 - 4 
89  3.58 - 3
90  3.56 - 2
91  3.53 - 1
92  3.50 - 0
93  3.46
94  3.38 
95  3.25
96  ----

 

[srolesen]

so let's say this is a 4 led indicator, and slightly analog in that each led dims rather than compleatly turns off as the battery drains towards the led threshold voltage. maybe it would be usefull to have indication of:
1) above 80% battery power (bright led if near 100%)
2) 50%-80% (2 leds will be bright, 1 led quite bright nearing 80%, 1 led off)
3) 30%-50% (1 led will be bright, 1 led quite bright nearing 50%, 2 led off)
4) 10%-30% (1 led will be quite bright nearing 30%, 3 led's off
5) 0%-10% (all led's off)
according to your test that would be:
led1 3.96V
led2 3.82V
led3 3.73V
led4 3.66V

looks like that wouldnt be easy to do with 1 color only :/

 

[Sci]

The LM3914 is the easiest way to achieve this. It can be run in bar mode, my 1st vid or dot mode, this vid from my early testing. Note, it's higher voltages, but still about a 1v range. I didn't have my adjustable power supply at that time. I was using a digital pot across the adjustment pins of a 4050 booster.

This also has fiber optics attached, but 3 3mm LEDs could be used for the same effect. The whole thing will be about as big around as a 14500(AA) battery but only half as long. The chip could be put anywhere in the mod with small wires running to the LEDs.

On a side note, I've got the TL431's(linked above) that I am going to work with this weekend. I'll post the results. The TL431s are about the size of a transistor.

 

[Sci]

I forgot to mention, that's tri-color LEDs in that vid.