Help with a flasher circuit with 555 Timer IC

Discussion in 'General Electronics Discussion' started by Alaa, Jul 28, 2015.

1. Alaa

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0
Jul 28, 2015

Hi Guys
The Purpose of this circuit :
1- Creating Low and Hi levels of lights with the three positions switch " SW1"
the 1st position will light up the upper group of LEDs " the two LEDs ", and 2nd position will light up all the exciting LEDs.

2- Creating a Flasher with the five LEDs together with " SW2 "

The problem is finding a way to connect leg 3 of the 555 IC with the five LEDs without affecting the first circuit.

2. duke37

5,364
771
Jan 9, 2011
My old brain is not too good so I had to find a book to remind me of what pin3 is. I deduce that it is the output.
The book also says that 4.5V is the minimum supply voltage for the 555.

The voltage required by the leds is not specified. It would be better to use a higher voltage and place a current control resistor is series with each led.

Diodes can be used to stop voltage going from one load to another but this involves another 0.6V drop.

3. Alaa

2
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Jul 28, 2015
Oh , It's Done
Thanks bro. ^_^

4. Colin Mitchell

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Aug 31, 2014
The transistor is doing nothing

4,960
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May 8, 2012

Chris

6. ramussons

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Jun 10, 2014
You are likely to burn off the B-E junction of your transistor.

7. Harald KappModeratorModerator

11,424
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Nov 17, 2011
There are a few issues with this circuit:

1. LEDs in paralle are not a good idea. The one with the lower pass voltage will drain most of the current, the other one will be only dimly lit, if lit at alll.
2. LEDs without current limiting series resistor are not a good idea. Without current limiting, the LEDs will draw too much current and will nurn. See our ressource section for more information on that issue and how to deal with it.
3. Add a resistor in series to the base to limit the currrent.
Apart from that, Q1 has no function at all. When sw1 is in the low position, it will drive a current through the be-junction of Q1 through LEDs D2, D3 and D4 (see above for that issue) and the LEDs wil be simply on, just as when sw1 is in the top position and LEDs D1 and D5 will be on. You can simply leave out the transistor, but don't forget the current limiting resistors, one per LED.
4. When sw1 is in the on position, the 555 is supplied with power, but nothing apparent will happen as the output pin 3 is unconnected.

What is it that you want to achieve with this circuit? Your explanation is not all too clear to me. Perhaps a table showing switch positions and LED function could be useful.

Combining logic functions of two (or more) switches can be achieved by logic gates or by some simple diode-transistor logic. This way you can combine the flashing output of the 555 with a constant control signal from the switches to let the LEds either flash, be on or off.

8. Alec_t

2,949
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Jul 7, 2015
Is this the sort of thing you want?

I've included a push-switch to prevent the battery being drained by the 555's standby current.

9. CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Just a guess Harald but I think you're going find a few issues with this one too.

Chris

10. Alec_t

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Jul 7, 2015
I'll revise the suggested circuit if you can identify the issues, Chris. (My interpretation of the OP's intentions may be wrong.)

11. CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Alec, when I viewed your schematic earlier I could have sworn the Trig pin was floating. I don't see that now. What's the Diodes for?

Chris

Edit: Another look and I see what D7, D8 (isolation) are doing but what's D8 used for?

Last edited: Aug 1, 2015
12. HellasTechn

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Apr 14, 2013
Why dont you just use the 555 in unstable mood and then just use the switch to connect the pairs of led's to the output (pin 3) with one resistor on the cathode of each led group ? that would make your leds flash when pin 3 goes high or low if you reverse polarit and use the resistor on the anode.

13. CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Alaa, just a bit curious. .. Are you designing a rear bike light with brake light capability?

Chris

14. Alec_t

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Jul 7, 2015
D8 provides a voltage drop so that the LED brightness will be the same whether the LEDs are turned on via the manual switches or the 555's discharge transistor on pin 7.

15. CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Just my opinion but it's a needless waste of power. Power is going to be dissipated with it or without it. I'd rather dissipate it in the LEDs. I cycle an average of 11,000 miles a year. My wife has been side swiped, knocked off her bike and injured. I've (by the grace of God) escaped these lunatics more times than I can count. In short,.. if there's battery power to burn I'd rather burn it in my LEDs.

Chris

Arouse1973 likes this.
16. CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
One other thought. I see you designed this with a 6V source. It would be more power efficient to series up some of those LEDs. Rear bike lights are Red LEDs.

Chris

17. Alec_t

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Jul 7, 2015
The 6V source was chosen for proof of concept because we don't know the LED type or spec, and the 3.7V source in post # 1 doesn't leave much headroom for current control if white LEDs are required.
Agreed, if we're talking red bike lights (the OP hasn't specified use or LED colour/spec) and efficiency then D8 isn't needed and series LEDs would work. There are several ways to skin this particular cat.

Martaine2005, CDRIVE and Arouse1973 like this.
18. CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Hi Alec, just so you know... I believe I'm a bit guilty of the "Peck The New Guy Syndrome". However, you took the pecking like a pro! I didn't detect so much as a little rattle in your replies.

Welcome!
Chris

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19. Martaine2005

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May 12, 2015
Hi Chris, Clearly you don't check you're fly zapper enough. Some smoke and others don't.
I prefer smoke!! Sometimes a banggg too.

Martin

20. CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Actually, I've been considering getting a Horror Freight swatter fryer.

Chris

Arouse1973 likes this.