LED flasher

Thread Starter

kuxz2008

Joined Nov 16, 2009
84
what is maximum number of led can i connect together if i want all led to flash at the same time with a 9volt battery source?
 

Thread Starter

kuxz2008

Joined Nov 16, 2009
84
now i am planning to add additional feature like a group of ledA will flash normally when the 555 timer is activated while another group of ledB will flash only when a '1' is detected.

how do i connect to the present 555 timer led flasher circuit?
i am thinking of using a transistor but do not know how to connect ....
 

Wendy

Joined Mar 24, 2008
21,847
There are many ways to do this. I just posted on a thread where someone wanted to use 24VDC to light a series of LEDs, but the 555 max voltage is 15V!

The solution I posted on post #9 is a good example of LED drivers. Be sure to drop the number of LEDs to something your power supply (was it 9VDC?) can handle.

http://forum.allaboutcircuits.com/showthread.php?t=32625

That same article I keep recomending you read covers basic LED theory on Chapters 1 and 2, and covers drivers on Chapter 10. If you want to learn electronics there no substitution for basic reading, it is fundimental. Once you learn something, the knowledge is yours, and it is something people can not steal.
 

Thread Starter

kuxz2008

Joined Nov 16, 2009
84
i have try out my thinking in multisim and it seems that it could not work...

the goal of my circuit is to enable the the led9 and led7 to start flashing only when the 5v vcc (J1) is on while led9 and led7 to stop flashing when (J1) is to ground. However i simulate the circuit and it seems that led9 and led7 keep on flashing even though switching the vcc to ground at (J1).

can you help me take a look at the circuit and find out whether did i connect correctly ....
 

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SgtWookie

Joined Jul 17, 2007
22,201
You need a resistor on the base of Q1.

You also need to limit the current through the LEDs on the emitter of Q1.
 

Wendy

Joined Mar 24, 2008
21,847
I assume LED1, LED3, and LED6 are white LEDs. White LEDs typically drop 3.6V (this is Vf). Add 3 together and you get 10.2V, which exceeds your battery voltage quite a bit. With White LEDs using a Vf of 3.6V 2 is the limit on 9V.

The other side, LED2, LED4, and LED5 have a different problem. A 555 can only get within 1.4V of the positive supply rail, so the output of the 555 is 7.8V max. Red LEDs have a typical Vf of 2.4 V (it varies a bit), so you have 3X2.4= 7.2V. The resistor is way too large to light them up right.

Wookie already mentioned the lack of a current limiting resistors on the other LEDs and transistor base.

All of this is covered in the article I keep referring you to.
 

Audioguru

Joined Dec 20, 2007
11,251
A 555 can only get within 1.4V of the positive supply rail, so the output of the 555 is 7.8V max.
It is not a 555. It is a Cmos LMC555 that has a max output high current of nothing when its output is at the supply voltage. Its output high current is not enough to light the LEDs directly but it can drive the transistor.
 

Wendy

Joined Mar 24, 2008
21,847
I missed the LMC designation, as opposed to the LM. A standard 555 can power LEDs, a CMOS can't.

Again, this was explained in the article. Why haven't you read it, you're just wasting our time and yours not doing basic research, when it has already been done and is in a really easy format?

I even have some schematics showing how to use a 7555 to power LEDs, but since you don't have the most fundamental basics down you're not going to get anywhere.

LEDs are simple. They are really simple. A 10 year old can figure them out, if they are willing to research the subject. Research in this context is basic reading.

The AAC book has a section on them, maybe you'd prefer to use it?

http://www.allaboutcircuits.com/vol_3/chpt_3/12.html

About 1/5th the way down.
 

Audioguru

Joined Dec 20, 2007
11,251
I mentioned the Cmos 555 because many new people don't know that it is a 555 with different (low output high current)) spec's. The circuit using the LMC555 to directly power LEDs might not work even if the LEDs are 1.8V red ones.
 

radiohead

Joined May 28, 2009
505
...or perhaps you could use LEDs that blink... just connect a current limiting resistor and a couple blinking LEDs to a battery and you have achieved your end state. If you need more voltage, use two 9V in series, be sure to adjust your resistor value.

By the way, you really should read Bills work... Just sayin'
 
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