Something like this.
The 5 LEDs indicate the % if time remaining in 20% increments. All LEDs light together and go out one by one at the timer times out.

Not even bench tested, just the concept.

Ken

 

Ken,u're great
Whats the VR value at each comparator,pin 4,6,8,10?
Cnt replace with fixed resistor ah?

 

Pin 4 is 7.0V
Pin 6 is 5.8V
Pin 8 is 4.3V
Pin 10 is 2.4V

These are approximate values assuming a fixed 12.0V battery supply...and the 555's time ending with 8.0V (12 * 2/3) across C2.

Yes, you can make voltage dividers with fixed resistors instead of trimmer pots.

Ken

 

Whats the VR value at each comparator,pin 4,6,8,10?

Sorry my mistake,
what i meant was the R value for the VR at those pins.
Those are variable resistor rite?

 

Voltage divider resistors for:
Pin 4 is 4.7K and 33k
Pin 6 is 3.3k and 10k
Pin 8 is 3.3k and 3.9k
Pin 10 is 27K and 12K

Worst case error with standard resistors was 3%...but we're not dealing with critical timing here...are we?

I used a resistance calculator called ResCAD: http://www.armory.com/~rstevew/Public/Software/ Very handy!


ken

 

Ken,im confused.
Why u give 2 value for each pin?
And whats the resistor value near the LED at the LM339's output?
What is the function of LM339 as a comparator?

 

The two resistors form a voltage divider, the same way as the trimmer pot, except fixed. This divides the +12V down to a fixed reference voltage that equals the voltage across C2 at a specific time the 555 cycle.

The comparators act as 5 step voltmeter. The voltages corresponds to 20% decrements of time in your case.

The comparators compare these reference voltages on their (-) inputs with the C2 voltage on their (+) inputs. If the C2 voltage is below the reference voltage, the comparators output is grounded and this turns on its LED. If the C2 voltage is above the reference voltage, the comparators output is +12V and the LED is off.

The resistors on the LEDs are 1K...for a 10mA LED current at 12V.

ken

 

U mean i has to combine in series 4.7K and 33k resistor for pin 4?

 

Like this. But remember that I have not bench tested this.

Ken

 

Thanks Ken.
The picture give me a lot of info,
Now i understand.

I got a question,
Lets say we took out the comparator circuit,n left will be a basic circuit.
This circuit i want to use for car,so its powered from 12V battery.
If i use for different power supply,lets say 9V or 24V,which component value do i need to change in order for the circuit to function normally?
The circuit u designed is for 12V supply.Will there be any effect in the timing or other aspect if i use 9V supply?

 

Since the 555 timing and the 339 comparator functions are all proportional to the the supply voltage, you can change the supply voltage without changing their component values. However the NE555 datasheet lists its "Absolute Maximum" supply voltage as 18VDC and the LMC555 (CMOS version) as 15VDC. So, 24VDC is out. The relay would need to be replaced with one with the correct coil voltage. In the range of 9VDC to 18VDC the LED current limiting resistors could probably remain the same.

Whenever someone mentions "9V" as a supply I immediately assume that they are thinking of small 9V rectangular batteries. These have a low amp-hour capacity and a circuit designed to run off of a 200AH/12V car battery may not work on a small 9V battery. This is where choosing LMC555 over an NE555, and other low-current draw components comes in. 30A relays are not going to be able to work for long with a small battery.

But, perhaps you have something else in mind....?

Ken

 

In earlier post u said LM555C n now u said LMC555.
Is the CMOS version is LM555C or LMC555?

But, perhaps you have something else in mind....?

Yeah you're right Ken,im thinking using this circuit for other application.

 

Actually I find the CMOS version of the 555 listed by National Semiconductor as both a LMC555 and a LM555C. Also, as a 7555 by other manufacturers.

Ken

 

Well i just found that the shop guy gave me LM324 actually.I dont know what the guy tought when i asked for LM339.Hmmmm.

Well Ken,can u explain to me abt the comparator circuit.Can it used as audio VU meter?I want to use the comparator for other circuit,how to calculate the resistor value so that it show the voltage i want.

 

The LM339 would only give you 4 levels (not counting zero to the first LED on) as a VU meter. It would be a matter of calculating the voltages for each step. You can expand that with another LM339 and more LEDs. If you want that, a simpler IC would be a LM3915. Already scaled as a VU meter to drive 10 LEDs.

Ken

 

Thanks for the info Ken.
Well my fren did a timer circuit(9VDC).
I told him abt the comparator circuit that u did,he dont know how to calculate the resistor value to be added so the LED light up as ur circuit above because his circuit is powered by 9VDC.
Can u help?

 

The scaling on the resistors is proportional and is the same for whatever supply you use. Those resistors will work from 5v to 18v supplies.

ken

 

All rite Ken.
Just want to make sure,there are 3 input for the comparator rite?
1 for +ve supply,1 for ground and 1 for signal(from capacitor)?