Battery indicator circuit

[Thunderchild]

I have designed the attached baterry indicator circuit for a 12 volt battry but for some reason in multisim it just won't work, was working before I put in the 100 and 200 R resistors in series and was just using a pot in their place.

The idea is that this will be used with a tri-colour led, so read is to come on under 12.5 volts and green is to come on over 11.5. so with a tricolour led between 11.5 and 12.5 both lights are on and it goes yellow/orange.

Any suggestions of what I'm missing ?

does anyone know of some good resources for design using comparators ? I can remember what the configurations can do but now how they are wired up.

 

[Mikebits]

**broken link removed**

 

[Thunderchild]

what about my circuit ? have I got it more or less right or made a hashup of it ?

 

[colin55]

Here's a simple circuit for your battery tester:


**broken link removed**

A very simple battery monitor can be made with a dual-color LED and a few surrounding components. The LED produces orange when the red and green LEDs are illuminated.
The following circuit turns on the red LED below 10.5v
The orange LED illuminates between 10.5v and 11.6v.
The green LED illuminates above 11.6v

 

[Mikebits]

I would use seperate vrefs for each compare circuit.

 

[Mikebits]

The way your circuit looks now, the low led will be lit even if the voltage is above 12v. I dunno, looks strange, I need to look at it more.

 

[Mikebits]

I think you could simplify your circuit if you use the same voltage source to both vin pins on the comparators, then use seperate vrefs, and invert the logic on the vlow side.

I bet I did not make sense. I am not very articulate at times

 

[ericgibbs]

I
does anyone know of some good resources for design using comparators ? I can remember what the configurations can do but now how they are wired up.

hi TC,

Look at these pdf:

 

[Mikebits]

The way your circuit looks now, the low led will be lit even if the voltage is above 12v. I dunno, looks strange, I need to look at it more.

I just realized I looked at the drawing wrong. You do have the vrefs swapped between compare circuits which is right. My eyes are getting bad...

D1 has me confused, wont it clamp the R1 R2 junction to 5v until Vbat drops below 5v? Maybe I confused myself...

 

[Thunderchild]

I just realized I looked at the drawing wrong. You do have the vrefs swapped between compare circuits which is right. My eyes are getting bad...

D1 has me confused, wont it clamp the R1 R2 junction to 5v until Vbat drops below 5v? Maybe I confused myself...

yes the zener is to create a voltage reference at 5 volts approx 1/3 the cicuits max and 1/2 the min, the 100 and 200 ohm voltage devider drops the battery voltage to 1/3 so that the 15 volt scale is adapted to the circuits 5 volt scale

 

[Mikebits]

Ericgibbs was kind enough to explain to me my confusion. Sorry for my dumb responses. Boy I feel silly.

 

[Mikebits]

Okay, I think I got it now, your 100 ohm is on the hairy edge of the threshold. You need a pot for the 100 ohm. With your circuit as drawn, I computed 3.666v and threshold needs 3.667v. More of a sim thing, I think you need a pot for the 100 ohm.

 

[Thunderchild]

Okay, I think I got it now, your 100 ohm is on the hairy edge of the threshold. You need a pot for the 100 ohm. With your circuit as drawn, I computed 3.666v and threshold needs 3.667v. More of a sim thing, I think you need a pot for the 100 ohm.

you need to bear in mind that the power supply will vary from 10-15.5 volts, I've tried a range of voltages and its just dead but I can't figure were I went wrong. I did have a pot for the 100 ohm one before but then got the circuit worked out to the correct voltage levels as before it worked when on low voltages like 2.5

 

[Thunderchild]

The way your circuit looks now, the low led will be lit even if the voltage is above 12v. I dunno, looks strange, I need to look at it more.

the low come on at 12.5 V but the high at above 11.5 so they are both on between 11.5 and 12.5 making it orange. Its a starngle logic I know but the most component efficient i could think of and quite accurate, but at present acording to multisim its stone dead

 

[ericgibbs]

the low come on at 12.5 V but the high at above 11.5 so they are both on between 11.5 and 12.5 making it orange. Its a starngle logic I know but the most component efficient i could think of and quite accurate, but at present acording to multisim its stone dead

hi TC,
Which circuit are you referring too.??

Your 1st circuit should work, does multism expect all the power pins on the LM339 to be connected.???

 

[Thunderchild]

yes I'm refering to my circuit. I don't think multisim wants all power terminals connected as I can't connect to the blank ones if I wanted to, as soon as I conected one VCC the red "X" appeared on the other and it would not connect to. like wise on GND. perhaps I'll try and make it in the flesh on a breadboard as i just have the components (well will have to dig out the leds from wherre ever I lost them)

 

[ericgibbs]

hi TC,

Check your LM339 input pins.
You have your Vref going to +in on one comp and -in on the other.????

 

[Thunderchild]

hi TC,

Check your LM339 input pins.
You have your Vref going to +in on one comp and -in on the other.????

well one needs to come on UNDER 12.5 volts the other OVER 11.5 its not a bar graph it will end up as a single tricolour led

 

[ericgibbs]

well one needs to come on UNDER 12.5 volts the other OVER 11.5 its not a bar graph it will end up as a single tricolour led

hi tc,
Just ran your circuit in LTSpice it switches over OK.

Are you expecting both LED's to be oN to give orange.???

Do you have LTSpice..?

EDIT:
Look at this, the green is the battery, red and blue are the LM339 output pins.

 

[Thunderchild]

Well i have multisim but can install LTSpice, last time I did though it was not exactly user friendly, but why won't it work in multisim then ?