My current problem

Morning all,

I'm hoping someone can help.

I am looking to control 8 sets of 13 bulbs using the arduino. I am confident with the coding of this and am planning to use relays to switch on and off each set of 13 bulbs.

I am trying to work out the best way of powering the sets of 13 bulbs. The bulbs are 3.5 with a current of 300mA.

Would it be better to power each set of 13 in parallel or in series? And for parallel/series what sort of power supply, and current are needed? Remembering that I also need to power and switch 8 sets of these bulbs.

These are the bulbs I wish to use as they fit with the theme of my project, a wheel of fortune. MES Bulb, pack of 50 – Kitronik Ltd

Thanks for any help you can give.


If run in parallel, you need a 4A 3.5v supply.

It would be better to use 4 on series and fed with 12v. Run 3 strings in parallel. I know this is only 12 lamps but that is my suggestion.


13 is a prime number.
So it's not possible to make two, three, or four strings with equal numbers of lightbulbs.
One single string is risky. When one bulb blows (they do!), the whole string is out.

Can you change your set to 12 or 16.

The whole setup will use ~110watt, not counting losses.
12volt/10A supplies are common/cheap (ebay).

Four 3.5volt bulbs in series would be perfect on a 12volt supply.
Brightness is slightly down at 3volt/bulb, but lifetime is a lot longer.

Arduino can also be powered from 12volt.

Look at the date. This is 2015. Why would you use incandescent globes?

"Warm White" LEDs approximate the colour of an incandescent globe if that concerns you. If you also want slow fade, you can emulate that in software (software PWM). The cost is much the same and you do not have to find sockets for them.

A TPIC6A595 should be able to drive strings of 5 parallel sets of 3 in series from 12V (with series resistors for each set of 3 or 1).

But if ya want retro, you have to use globes/lamps.
I haven't seen an LED that has a nice warm element in a glass envelope.

Tom..... :slight_smile:

4 sets of 3, and 1 single.
Sets of 3 use 5 ohm current limit resistor.
Single uses 28 ohm current limit resistors.
1.5A/13 bulbs

8 set = 12A, use 2 12V/10A supplies, 4 sets on each one.

There are constant current voltage-boost converter chips that are designed specifically for driving a
dozen or so power LEDs in series...