multiple 555 timers, same +/-

[dylar]

If I'm just using them to time LEDs is there any reason why three or more 555 circuits can't use the same +voltage and ground?

Also, can someone tell me how to calculate the required voltage for 6 555 timers that light 2 LEDs each? Don't need an exact number, just wondering if a 9v adapter would do the trick.

[pjwhite]

There is no reason you couldn't share power and ground connections.

A 9V DC adapter should work, though I wouldn't expect to get very regular timing is it is unregulated.  If you need accurate timing, use a regulated supply.

If your LEDs are wired in parallel to the 555 output, a 5 volt supply would be enough.  In series, and the 9V supply would be a better choice.
Be sure to put a resistor in series with the LEDs to limit the current.  I'm sure there are lots of posts on this board to tell you how to calculate the resistor value.

[defaced]

Read the datasheet, but you'll probably want to give every 555 a decoupling capacitor (0.1u ceramic or film) between power and ground.  These caps get located physically close to the power/ground pins on the 555.  You can read up on decoupling caps more, but basically they will keep any junk from the chips from entering the power rails and possibly interfering with other chips.

[dylar]

Thanks!
Does this still apply given that the 555 circuits are not in the audio signal path? (using homemade vactrols).  Without decoupling will there be enough interference to change the flash rate of the LEDs?

[defaced]

In this case, it's a digital IC etiquette thing.  If you look at most projects with digital ICs, they will have this cap.  It's nothing to do with audio or the LEDs, it's just to keep the chips from dirtying up the power rails.  Other typcs of circuits (analog IC and even tube circuits) have decoupling caps of different values in different places but all for similar reasons.  For digital chips (the 555 is a CMOS chip), a 0.1u cap connecting between power and ground located right next to the chip's power and ground pins is a standard decoupling approach. 

[deadastronaut]

@mike. nice tip. would that stop any (notorious 555) ticking in an audio application though?....just curious. cheers rob.

[mr clack]

Also a 7555 is meant to have less affect on the supply

[defaced]

@mike. nice tip. would that stop any (notorious 555) ticking in an audio application though?....just curious. cheers rob.

I've never worked with 555 in an audio application. Do you have a schematic you can post or reference to?

[deadastronaut]

@mike. nice tip. would that stop any (notorious 555) ticking in an audio application though?....just curious. cheers rob.

I've never worked with 555 in an audio application. Do you have a schematic you can post or reference to?

hmmm not at the moment, but i have used 555's to flash leds into ldr's..for tremolo type stuff...i had ticking with standard 555's..

then i used tl555cn low noise cmos and they were better....but now i experiment with opamp lfo's just to avoid these noise/tick issues!...