Multiple circuits using one power supply

[vwguy16]

Hi,
I recently started to get into electronics with help of a PC program that allows you to design and test circtuits.

The circuits that I made are to simulate running lights on a model starship:

the primary LED flasher circuit that uses a 555 timer to flash 10 LEDs on and off every couple of seconds

A secondary flasher(555 also) that briefly flashes 4 LEDs on for half a second every 3 seconds

a fade in circuit..ie when power is applied the leds will take several seconds to fade up to full brightness.

The idea was to put all 3 circuits inside my model and run the wires down the stand to a single switch and a 9v power supply.

I had great success making these circuits and when i actually built them using real components they worked as well as the program said they would...individually....

However, I wanted them to all run off of a single 9v power supply. Problem is if I connect the + wires for the two flashers together and the - wires together and apply power something goes wrong...the primary flasher does not behave the same..in that the flasher seems to be faster and the primary LEDs will turn off when the secondary LEDs turn off...so im guessing something is interfering....

do i need to isolate the separate circuits somehow ? if so how do i do this?

Any help would be great !!

Thanks,
Andy

[Thomas W]

Hi Andy,
please post the three circuit diagrams.

[I_Daniel]

Is your power supply well regulated ? or does it fluctuate ?
Can it provide the amperes for all the circuits ?

A large capacitor say 470 Mfd and a .01 Mfd capacitor across the power supply and a choke in the positive line may help to decouple the power supply. But as you have not given any specific circuits this is just a wild suggestion.

[JMACgyver]

Howdy,

A normal 9-volt battery will only supply ~150mA to any given circuit (if needed)

Parallelling three circuits on it bring each circuit roughly 50mA, I'm sure much lower than the circuit needs, hence the erratic behavior. See if six AA cells instead of the 9V helps at all.

In addition to the capacitor and choke mentioned, another choice may be to wire in a diode along the negative wires going to each circuit. (Cathode to battery of course) this may help with any feedback from one circuit affecting the others. Might try the positive line if that doesn't work.

Regards,
--Electro--
aka David M.
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