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Simple 12v battery level LED indicator w/ A single 555 IC, none on the net. (555 is for looks) is it possible? Answered

Well im somewhat novice and I was wanting to make a circuit to monitor the level of a 12v car battery with 3 LEDS (although more is cool) Yellow for low, Green for good and red for overcharge.

Ive looked all over and cannot find a circuit that uses a single 555 ic to do this easy task.


5 Replies

metal_head_mike (author)2012-04-19

the LM339 is a good IC to monitor automotive voltage.
you can buy a kit from Thaishine that is made for 12v systems, or make it yourself with the LM339 IC. I have the kit but havent had the time to make the circuit yet. there is not much to the kit so it should be easy to build.

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the 555 IC is a single timer, a timer wont do anything for monitoring voltage,
i think for what he wants, he should use an LM339 Dip IC, i have this kit that is made for 12v automotive systems and it does the job well.
here is a list of items that are needed, or included with the cheap kit.

Part List: 12 volt Battery Monitor.
1x L78L05 5v 100ma Voltage Reg.
1x LM339 Dip IC
2x 220 ohms ¼ watts resistors
1x 14 pin dip socket
1x 8.2K ohms ¼ watts resistor
1x 100uf 25v elect-cap
1x 47K ohms ¼ watts resistor
1x .1uf ceramic cap.
1x 24K ohms ¼ watts resistor
1x 470uf 35v elect-cap
1x 33K ohms ¼ watts resistor
2x 1N4148 diodes
1x 10K ohms ¼ watts resistor
1x 10K trimmer pot single turn
1x small preformatted board
1x Red 5mm LED 1x RED 3mm LED
1x Green 5mm LED 1x Green 3mm LED
1x LM317T Voltage reg.(to-220)
1x 2k trimmer pot
1x 150 ohms ¼ watt resistor

with these parts you can build a very good voltage monitor,
Green Led Light indicates charging of battery(s) and lights at 13.25v.
Red LED Lights and buzzer sounds at 15v or higher
and indicates probable overcharging that will damage your battery.

you can also buy the kit for about $16 + shipping.

the LM3914 IC's are great for bar/dot graphs, you can use them for monitoring voltage also, i built a meter for my 2x 2600farad caps at 1300f 5v and its on right now showing the voltsage drop on the caps.

a LM3914, a 6x6x11 momentary button or jumper, 3 resistors, two jumpers and a 10 segment bar grapg. thats it, its good for visual, but had no real monitor beside a bar graph view, a buzzer will allow you to hear when the charge is either going over volts or under. the kit above provides visual and audio and you can set it for any volts you want to monitor.

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steveastrouk (author)2012-02-20

Expanding on Rick's comments: you want a window comparator.

Or, for 10 LEDs, you need an LM3914 bar graph chip.

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Sky Graham (author)steveastrouk2012-02-21

Thanks for the replies guys, I researched the op amp, got some experience there, aswell as the LM3914. I am not at that level yet.

Im aware of the 555 being unsuited for this purpose.

But I really do just want to incorporate the 555 into this really simple circuit here
(its the first one)

No special purpose, maybe make an LED blink for battery low.
I am at the learning stage of 555 making led's blink, change brightness, fade - I know this is easy but aarrrrr..... I will get it

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rickharris (author)2012-02-20

Wrong IC you want an OP amp.

Whole set of circuits here


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