totally_clueless

Hi all, ok, yes first post and maybe asking too much but am well stuck tbh...

Bit of background, got a heap of LED's, some 555's, some stripboard pile of resistors n caps. Just need to know how to put them together

What am I trying to do !?

Ok, am trying to make an indicator "pack" for a bike, idea being able to flash 20 leds , being able to switch off but also to have an "auto off" after approx 60 seconds..

So, from what I've read so far will need a 555 setup Astable, 750ms on and 750ms off..

then another timer that is triggered when the indicator circuit is triggered and resets the indicator circuit after the preset time...

Maybe that should be the other way round ?

So the main timer is triggered by the indicator switch, which triggers the indicator circuit??

AM a bit lost to be honest as to how to get it all to work together and the best way to do it..

Can anyone help out a neewbie please ???

TIA

totally_clueless

totally_clueless

Ok, so having a dig around and finding circuits I need...

astable



R1 = 1ohm (I think !)
R2 = 820ohm
C = 1uf

Pulse should be .8 (ish)

Does that look/sound about right ??

Now that should be triggered by a monostable right ? lol...

Should anyone reply, please assume I am a complete numpty !!!

AllVol

Hi, totally. Your circuit looks good. Go ahead and put it together, although I would recommend building on a cheap, plastic breadboard like from Radio Shack. That way you can change quickly if you see you've made a mistake. I think your choice of resistors is wrong for the time you indicate, but try it out. don't be afraid to play around with values. You can't really hurt anything.

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Roff

Are you wanting turn-signal indicators for a motorcycle? If so, how many LEDs per side will you have (you mentioned 20), and how much current do you want to pass through them? Is this powered frm a standard 12 volt sealed-lead-acid battery?
And don't be too sure that Allvol is correct about not hurting anything. I think R1=1 ohm may smoke either the resistor, or the 555.

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Ron

kchriste

Breadboard up the above circuit and try out these values:
R1 = 1K (1000 ohms)
R2 = 220K (adjust to get the flash rate desired)
C1 = 1 uF 16V to 50V

Don't go much lower than 1K with R1 as this will cause pin 7 of the 555 to draw too much current. To drive 20 LEDs it will be best connect them in series/parallel to save on current and minimize power dissipation in the current limiting resistor. The bipolar 555 will only give around 200ma out of pin 3 so you may need a power transistor for more current. What is the nominal current rating for the LEDs? Some super brights can take alot of current while plain Jane LEDs usually should be limited to 20ma or less for longer life.

Oznog

You MUST have an output transistor- bipolar or MOSFET- here. A 555 output can barely drive 1 LED, much less 20 powerful ones.

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audioguru

Can you imagine seeing 20 1W Luxion LEDs on the back of a bicycle at night? You would be blinded and the battery would be huge.

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k7elp60

I think you can do it with 2ea 555 timers IC's. One as a one-shot for the auto off at 60 seconds, and the other one as the flasher.
If my memory serves me right a regular 555 can sink or source 200Ma, thats a bunch of LED's.
Several of my reference sources recommend the minimum value of the resistor
from pin 7 to Vcc to be 1K.

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Hero999

A standard 555 can supply 200mA, which is 10 LEDs @ 20mA and 20 @ 10mA, or connect the LEDs in series and double your LEDs, no output transistor is required!

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