Battery level indication : a circuit

[kinabaloo]

Here's a circuit to indicate battery level. Haven't made it but so simple that it can be designed well just on paper.

I thought of using a quad op-amp that comes in 1 x 14 pin chip (get a socket too and solder that) to give a four LED level indication; one could use green, amber and red LEDs.

An op-amp is a comparator circuit. It will compare actual voltage to a known value(s). To get a fixed reference we use a zener diode. This needs to be less than the lowest the battery will go (about 3v - to 3.5v) so let's say a 2.7v zener.

Now, if a 3.7v lithium is freshly charged it will be abut 4.2v. So the first LED could indicate a value of say 4v or greater. How to do that if our reference is only 2.7v? By dividing the voltage with 2 series resistors (or more than two to get a sequence of fractions; we do the same with the reference voltage). Put an LED on each op-amp output and connect the power lines to the op-amp chip.

A simpler single op-amp circuit could be made instead that will detect when the voltage is nearing needing a recharge.

To have the LED come on when power drops below rather than the reverse, swap the + and - on the op-amp.

Very simple! The trick is to realise tha one can work on fractions of the supply voltage.

BTW, resistors these days are all 1% as standard.

 

[kinabaloo]

ps: Across the four black resistors next to op-amps is 2.7v. Use these to give a suitable scaling, such as 95%, 90%, 85% and 80%; The bottom resistor will be the highest; Use values in the 1k to 47k range.

Similarly the two blue resistors will divide the actual battery voltage so that the ratio is 4/2.7; i.e. the voltage at the divide is 2.7v when the battery actual voltage is 4v; this will light all four LEDs (just).

I'll let you do the math

If worried about power use, you could raise the 82 resistors to 220 or 330 and choose high brightness LEDs; or put the whole thing on a push-to-make button.

pps: I've only drawn one of the 4 outputs; do same on the outputs of the other opamps.

 

[Laredo7mm]

Here is the one I use:

 

[kinabaloo]

Laredo - interesting - can get a chip for this now!

But it's basically just an opamp and a zener diode in one

But same principle.

A bit mean with the LED current though !

 

[kinabaloo]

I'm thinking that a NicoStick box has enough space for an MP3 chip, amplifier and small speaker so am wondering about some suitable sounds effects to accompany each puff ... something the sound of a blowtorch perhaps ...

 

[Laredo7mm]

Yeah, it is a nice little chip. It came in soic8 format so I bought it. For some reason I really like that chip size. In my PV Pak, I had it turn on at 3.1V with a 3.1V forward voltage LED, so I don't even run a current limiting resitor.

 

[kinabaloo]

Yeah, it is a nice little chip. It came in soic8 format so I bought it. For some reason I really like that chip size. In my PV Pak, I had it turn on at 3.1V with a 3.1V forward voltage LED, so I don't even run a current limiting resitor.

The main problem with ready made chips is not only need to get hold of them but also that one might not be able to achieve quite what one wants sometimes. So i like to build things from the simple building blocks - trannies, diodes, opamps; perhaps splash out on a timer or logic gates

 

[kinabaloo]

For example: thinking that a recharging circuit could be much the same as the level circuit - suitable current feeds on each opamp o/p to slow recharge as it fills. Could even keep the LEDs to indicate progress.

 

[solonguniverse]

I'm thinking that a NicoStick box has enough space for an MP3 chip, amplifier and small speaker so am wondering about some suitable sounds effects to accompany each puff ... something the sound of a blowtorch perhaps ...

Lightsaber sound effects!

 

[ichaya]

OK, for those of us that are NOT electrical engineers!


WHAT???

I would be interested in something that showed my charge progress, and also when it was time to re-charge.

However the previous conversation has me lost.

 

[kinabaloo]

OK, for those of us that are NOT electrical engineers!


WHAT???

I would be interested in something that showed my charge progress, and also when it was time to re-charge.

However the previous conversation has me lost.

It would do that

 

[m68thomas]

For those of you that dont want to spend that much time in development. this is small enough to fit in a niko stick.
Ive been flying all kinds of radio control for many years. volt watch is 11.00 and you can pick up at your local hobby store.

towerhobbies dot com volt watch

 

[kinabaloo]

Quad op-amp: $1 plus 4xLEDs and 4x resisitors. Total $3

 

[dedmonwakin]

Awesome schematics....but I can't read it,
This is something that I would love to incorporate for the cool factor, although I know it would be overkill. Mini Red LED DC 100V Digital Volt Voltage Panel Meter - eBay (item 350064809260 end time Jul-22-09 12:23:01 PDT)
Only thing is it needs it's own power source....or, if I knew how to. The mod could use a higher voltage battery with enough to supply the digital voltage meter and split off to the ecig or something like that...I dunno, but I pretty much scrapped the idea since I wouldn't know where to begin.

 

[kinabaloo]

Awesome schematics....but I can't read it,
This is something that I would love to incorporate for the cool factor, although I know it would be overkill. Mini Red LED DC 100V Digital Volt Voltage Panel Meter - eBay (item 350064809260 end time Jul-22-09 12:23:01 PDT)
Only thing is it needs it's own power source....or, if I knew how to. The mod could use a higher voltage battery with enough to supply the digital voltage meter and split off to the ecig or something like that...I dunno, but I pretty much scrapped the idea since I wouldn't know where to begin.

Will probably work ok on 3-4v, but can't say for sure.
Will probably work ok with input voltage same as supply voltage, but again can't be sure.

 

[m68thomas]

Quad op-amp: $1 plus 4xLEDs and 4x resisitors. Total $3

Quad op-amp: plus 4xLEDs and 4x resisitors. $1
2 weeks of frustration hair pulling and crying: priceless

talk about the elephant stamping around the room.

 

[kinabaloo]

Quad op-amp: plus 4xLEDs and 4x resisitors. $1
2 weeks of frustration hair pulling and crying: priceless

talk about the elephant stamping around the room.

i know your meaning - lol

but getting it going ... priceless !

seriously, this might look a bit complicated and it will take a bit of time. But it will work and as circuits go is quite simple.

I thought that because the design is basically just comparators and these can be easily understood (unlike transistors say) it was feasiblr even for an electronics novice.

 

[kalc]

Here's a circuit to indicate battery level. Haven't made it but so simple that it can be designed well just on paper.

I thought of using a quad op-amp that comes in 1 x 14 pin chip (get a socket too and solder that) to give a four LED level indication; one could use green, amber and red LEDs.

An op-amp is a comparator circuit. It will compare actual voltage to a known value(s). To get a fixed reference we use a zener diode. This needs to be less than the lowest the battery will go (about 3v - to 3.5v) so let's say a 2.7v zener.

Now, if a 3.7v lithium is freshly charged it will be abut 4.2v. So the first LED could indicate a value of say 4v or greater. How to do that if our reference is only 2.7v? By dividing the voltage with 2 series resistors (or more than two to get a sequence of fractions; we do the same with the reference voltage). Put an LED on each op-amp output and connect the power lines to the op-amp chip.

A simpler single op-amp circuit could be made instead that will detect when the voltage is nearing needing a recharge.

To have the LED come on when power drops below rather than the reverse, swap the + and - on the op-amp.

Very simple! The trick is to realise tha one can work on fractions of the supply voltage.

BTW, resistors these days are all 1% as standard.

Nice, u hav made a 2 bit flash ADC for e-cigs

 

[kinabaloo]

Nice, u hav made a 2 bit flash ADC for e-cigs

Well, a quasi-digital, 2 bit (2 to the power of 2, i.e. 4) Analog to Digital Converter.

Though output would be

0000
0001
0011
0111
1111

so actually 2 and a bit bits, rather than the usual 4 bit

0000
0001
0010
0011
0100
0101 5
0110
0111
1111 15

 

[kalc]

Well, a quasi-digital, 2 bit (2 to the power of 2, i.e. 4) Analog to Digital Converter.

Though output would be

0000
0001
0011
0111
1111

so actually 2 and a bit bits, rather than the usual 4 bit

0000
0001
0010
0011
0100
0101 5
0110
0111
1111 15

Right, excellent. Keep up ur good work , i enjoy reading ur posts