# HELP NEEDED - Busy Box With Led Switches

#### TheChoreographer

Joined Mar 31, 2022
10
Hi guys,

I wanted to know the most efficient way to connect this up. The LED switches are 12v and the 2 AA battery supply is 3v. Will resistors be necessary or not?

Many thanks

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#### AlbertHall

Joined Jun 4, 2014
12,023
Welcome to AAC, @TheChoreographer
The switches may or may not have resistors buit in.
Can you give us a link to the switches?

#### dl324

Joined Mar 30, 2015
14,467
Welcome to AAC!
Will resistors be necessary or not?
The listing said they don't include current limiting resistors:

Naturally, they don't give any data on the LEDs...

#### TheChoreographer

Joined Mar 31, 2022
10
Welcome to AAC!

The listing said they don't include current limiting resistors:
View attachment 264011
Naturally, they don't give any data on the LEDs...
Thank you!
Ah yes, I actually asked that question on there and didn't realise someone answered! Now I just need to figure out how to do it

#### panic mode

Joined Oct 10, 2011
2,135
just pick couple of resistors, start with 1k. if it works but it is dim, chances are they already have resistor built in. measure current and choose lover value resistor as long as current is reasonable (less than 20mA).

btw one of the pictures shows switch lighted up with 9V battery. i would expect this to have the series resistor.

#### dl324

Joined Mar 30, 2015
14,467
I actually asked that question on there and didn't realise someone answered! Now I just need to figure out how to do it
If the LEDs aren't white or blue, assume a forward voltage drop of 2V and a forward current of 20mA (I assume you'd want them bright for more entertainment value). Use Ohm's Law to calculate:

$$\large R = \frac{V} {I}=\frac{V_{supply}-V_{LED}} {I_{LED}}=\frac{3V-2V} {20mA}=50\Omega$$

The forward voltage of the LEDs will likely be higher than 2V and the battery voltage will be less than 3V most of the time. If you're inclined to omit the resistors, don't because AA batteries can provide enough current to damage an LED.

Regarding wiring. It's unclear to me whether the LEDs are only on when the switch is closed.

Last edited:

#### djsfantasi

Joined Apr 11, 2010
8,325
I’d get rid of the 2xAA battery holder and replace it with a 3xAA holder. That gives you more voltage headroom for controlling the current to the LEDs. Plus, more operational range for when the batteries start to die.

Calculating the required resistors has been described in another post, so I won’t go into it again unless requested.

#### Audioguru again

Joined Oct 21, 2019
4,688
Of course the LED in the switch has a series resistor designed for 12V. The LED will be extremely dim with only 3V and probably not light when the battery voltage drops to 2V. The blue LEDs might not light since many of them need at least 3.2V.

The switch has two terminals for its switch and the third terminal for the cathode of the LED.

#### djsfantasi

Joined Apr 11, 2010
8,325
Of course the LED in the switch has a series resistor designed for 12V. The LED will be extremely dim with only 3V and probably not light when the battery voltage drops to 2V. The blue LEDs might not light since many of them need at least 3.2V.

The switch has two terminals for its switch and the third terminal for the cathode of the LED.
So how do you explain post #4?

#### Audioguru again

Joined Oct 21, 2019
4,688
So how do you explain post #4?
The listing does not say the switch does not include the resistor, an idiot answering said it wrong.
The LED will instantly burn out without a resistor when 12V is applied.

#### TheChoreographer

Joined Mar 31, 2022
10
Thank you for the advice guys... the switches only illuminate when switch is turned on I believe. Still not clear whether it has a resistor built in or not. Perhaps someone out there that's used this exact style of switch can confirm before I get the resistors. Anyhow, when wiring up, just solder all 8 negative wires to battery negative and all 8 positive wires to battery positive? Will use heat shrink tubing also and use a 3x AA battery pack.

#### Audioguru again

Joined Oct 21, 2019
4,688
The switches are made for 12VDC so the LED already must have a series resistor inside the switch. They say the LED will turn on when the switch is turned on. Use 12V, not 3x AA.

#### djsfantasi

Joined Apr 11, 2010
8,325
The switches are made for 12VDC so the LED already must have a series resistor inside the switch. They say the LED will turn on when the switch is turned on. Use 12V, not 3x AA.
I agree. I recommended 3xAA when I thought there was no internal resistor

#### Ya’akov

Joined Jan 27, 2019
5,663
If you have a DMM with a diode test range it may answer the resistor question. Many DMMs provide enough voltage to light the LED when testing. It it does then there is no resistor, if it doesn’t the result is ambiguous.

If you have an LED to check the DMM that would make things more clear. If the DMM lights a white LED it would pretty much guarantee that the switch would light when tested.

#### TheChoreographer

Joined Mar 31, 2022
10

#### Audioguru again

Joined Oct 21, 2019
4,688
Eight AAA alkaline batteries are expensive. A timer circuit should be included to turn it off when it is not used.

#### TheChoreographer

Joined Mar 31, 2022
10
I opened up a switch and couldn't really see a resistor. Can someone draw me up a basic diagram on how I can wire this circuit up please I'd really appreciate the help

#### Ya’akov

Joined Jan 27, 2019
5,663
I opened up a switch and couldn't really see a resistor. Can someone draw me up a basic diagram on how I can wire this circuit up please I'd really appreciate the help
Do you still have it open? Can you take photos? Just to be sure.