Hi.
Forgive this idiotic question, I am a complete numbskull on this topic and have to Google and spend hours researching the simplest electronic problems.

My issue is this.
I have torn open a 3rd Gen Amazon Echo Dot and fitted it in an old 1948 radio chassis (the chassis components and wiring etc was basically destroyed so it wouldve just gone to the tip, I take pity on things like this).

I have the Echo Dot fitted in the chassis with an external speaker and it works well apart from one niggling problem.

The radio originally had a 6v dial lamp. Ive put in a small LED and found that when its powered at 3.5v it gives off a nice dim light similar to the original incandescent 6v bulb but at almost half the power.

Now, I obviously have the Echo Dot power lead going into the radio chassis to power the Echo Dot and I do not want another lead going into the radio just to power the dial LED.

Im wondering if I can splice open the Echo Dot lead and spur off from its 12v feed to the Echo dot and use the spur to power the Dials LED?

However, somewhere in my brain I believe Ive read that any resistors I use (on that spur) will produce heat and Im also wondering if the Echo Dots 12v requirement will be compromised if I split off to power the LED. Hence the little project has now stalled due to my lack of talent.

Any advice greatfully accepted. I should add Im in the UK with a 236v wall outlet but the Amazon plug quotes a 100-240v 0.5A 50/60Hz input and a 12.0V 1 25A output.

Thank you. (All this fuss just so i can have a little dial lamp lol .... but it just wouldnt be right without one.)

 

If you are actually running the LED on 0.0008A (0.8mA) of current, then a simple dropping resistor from the 12V supply should be fine.

If you are sure the 12V supply is DC, you can use a 10k resistor to reduce 12V to 3.5V at 0.8mA. The resistor will generate heat, but only a tiny amount since the current is so low. It will not affect the 12V supply.

 

You need either the equation P = IV, i.e. Power = (current x voltage) --OR-- P = (I^2)R Use this to calculate the heat that will be generated by the resistor. For the first equation, voltage will be the voltage drop across the resistor. For example, if you use a 10k resistor and you measure .00085A, the heat will be (0.00085^2) * 10000 = 0.007W. As mentioned above, this is a teeny tiny amount of heat, not enough to think about at all.

 

Other options would include using a similar wattage rated 12 volt light, or even a "warm white" LED with a suitable resistor.