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superchiku
04-07-2008, 02:18 PM
i want to built a simple battery monitor using Lm3914 but the schematics i have seen so far in the net is for 12v batteries, i want to make it monitor a 9v or a 8.4v battery , so what changes i should do so that it can monitor these volatage ranges or any range i want??

jitun
04-09-2008, 01:35 PM
Long ago i was working on a wireless hand held terminal and had a battery status display on the LCD. I simply used the ADC of the PIC18F4320 to measure the battery voltage.

http://i25.tinypic.com/27ywc1z.gif

Here is a page that can help you make a simplified battery monitoring circuit.

http://www.qsl.net/yo5ofh/pic/battery%20monitor.htm

any PIC microcontroller with ADC will just work fine. PIC16F88 will be fine. I can't open the code for the bat monitor in the above page. But if u understand the logic you can write it.

superchiku
04-09-2008, 01:57 PM
well since i have never used lcd bfore , i dont know how to interface with the lcd , thats why i was thinking of using the lm3914 coz this circuit will be constantly attached to the main circuit hence i cannot afford to waste some adc channels and normal io pins for battery monitor as the main circuit is going to take a considerable amount of io pins

jitun
04-09-2008, 02:01 PM
No need to use LCD. see the page

http://www.qsl.net/yo5ofh/pic/battery%20monitor.htm

Its using 8 LEDs to show the status of the battery. You can do that

And make a separate ckt for battery monitoring using PIC16F88.Its a 18 pin mcu so it will take much less pcb space and u can use its adc channel and the IO pins for the LEDs

superchiku
04-09-2008, 02:16 PM
well i dont know how to use pic i work only with avr's , yes i can do that with another avr but u see i dont want to buy another atmega and program it

it can be much cheaper using lm3914 but thwere will be one advantage that the coding will be very easy while using a mcu

jitun
04-09-2008, 02:28 PM
You can get a pic16f88 for around Rs100. But the problem is u don't know how to write program for it.

superchiku
04-09-2008, 02:37 PM
it wont be a problem ill replace the pic with an avr coding is no problem just that i didnt want to use a mcu as with a lm3914, i can give battery voltage to a max of 12 v but since the adc can recognise a max of 5v , ill have to use a pot which is directly connected from the battery to the adc to minimize the voltage

asimov_18
04-10-2008, 01:48 AM
Hi I had built this curcuit for measuring the voltage of a 12V battery when I was in college mind u lm3914 was around 40-45 buch for this price u could buy and use an atmega8. But if u were really keen on 3914 then u could make the same circuit using 3914. all u need to do is adjust the trimmer used for calibrating the circuit. Yes I remember I had used a bench power suppy(adjustable one and a tek multimeter from lab to caliberat the thesh hold voltage of that) U could caliberate the same circuit for 8-9V shouldn't really be a problem. If still any issue send me a post i will answer this issue. Use a good quALITY trimmer (10 turn bourns brand)for circuit as this is imp for accurate caliberation.

the circuit diagram is present on the following site: http://www.uoguelph.ca/~antoon/circ/batmon12.htm


asimov

superchiku
04-10-2008, 06:16 PM
thanks for the post , can u exactly tell me how i calibrate the threshold using a trimmer and which pins should it be connected to

asimov_18
04-12-2008, 10:11 PM
HI buddy.....well trimmer is juast a kind of variable resistor( search for "10 turn trimmer pot photograph" on google).......and as far as the caliberation goes the link gien had enough of that....any ways connect the circuit(asfter construction) to a variable voltage supply(high/good precision proffesion power supply). In parallel connect a good multimeter(I had used a tektronik multimeter). since u are trying to make a 9v battery monitor adjust the power supply volatge to 9V(or 8.4v what every be the standard volatge of the battery when charged). now turn the trimmer screw until all the led (10 of them light up, hoping you are using circuit in bar graph mode).

PL NOTE I has some problem with this circuit/all circuit which monitor batter voltages. I was using a 12V 32A car battery to run a dc motor(with fan, a car radiator fan motor with 12 7Amp rating) as the internal resistance made a terminal voltage of the battery drop when the fan was running and so the this voltage monitor gave false reading when connected to floating battery terminals and when connected to loaded battery volatge terminals.........


if you are running light load this shouldnt really be a problem.....[/img]

superchiku
04-12-2008, 11:41 PM
well friend thanks so much for the help , are other kinda battery monitors possible , i heard that u can make one with the ds**** some chip where u can also see ur battery's temp on the lcd

debu
04-13-2008, 10:32 AM
Why make such expensive and over-engineered battery monitors? :lol: A battery monitor circuit should not cost more then Rs.5!! (In terms of component price).

Use a simple zener-led circuit.

Schematic (clickie) (http://img205.imageshack.us/my.php?image=schematiciw8.bmp)
Layout (clickie) (http://img201.imageshack.us/my.php?image=layoutkj2.bmp)

Regards,

Debu :)

superchiku
04-13-2008, 01:09 PM
annother monitoring ckt, thanks did u design it?

debu
04-13-2008, 02:16 PM
Yes, Thats why it has my name all over it. :lol:

Regards,

Debu :)

superchiku
04-13-2008, 05:54 PM
are you an engineering student or u passed out, can u tell me how it works?

debu
04-13-2008, 07:07 PM
@superchiku: I passed out 2003. :lol: . I've an M.S. in Embedded Systems.

The circuit is quite simple, there are 5 zeners, as the voltage drops, below each zener's rating, it stops the flow of current, and switches of the respective LED. If you see the schematic carefully there is a different rating for each zener, and a different rating for each resistor driving the LED's. Each resistor must have a value such that after the zeners voltage drop, we drop the voltage further to drive the leds. Pretty simple really. No need to go in for an ADC and all that rot.

Regards,

Debu :)

asimov_18
04-13-2008, 10:46 PM
Hi folks,
debu is right to some exting ideally a voltage mointor should be cheap. Probably 5 Rs. But techinically speaking it depends on the requirement. Like if you are moitoring charging of a lithium Ion battery one need a very precise voltage of about 4.2V. One could surely make a simple circuit(simple voltage compartor) using an op-amp and a zenner diode/other voltage reference source and a few resistors...but super chikku seems to be interested in using lm3914......so be it...........

superchiku
04-14-2008, 01:39 AM
well LM3914 provides a more universal approach coz i can use this circuit for any volatage betn 0-12 , but debu's circuit can be used for specific voltage ratings avvording to the type of zener diode used..

I also heard abt an intelligent battery monitor using DS**** some name i dont remember, so i would also like to have a tutorial on that too.. so asimov and debu you have helped so far can u say how exactly i use The DS**** microchip?

Vivek
04-14-2008, 09:25 PM
Debu,

Your schematic shows the zeners reversed. (ie they are forward biased.)
All the Leds will be always on. reverse them.