Seperate Project Concurrent With My Wedding Project

So the wedding project is still going. Soldering as many LEDs as I am is time consuming and I just had a heat shrink snafu where I ordered the wrong size and not nearly enough to finish my project so I ordered the right size and quantity and expedited shipping hopefully it gets here in time.

I'm also making a wedding present that doesn't use an Arduino but just LED's in series with an on off switch and I was hoping someone could double check my math.

I'm going to wire up 20 white LEDs in series and I was hoping that I could wire all that up to a 110V lamp cord with an on / off switch wired in to it and a 300K resistor.

Also is silicone sealant conductive? As in can I put a small dab of silicone on the back side of an LED to secure it in place and if it bridges the gap between the two leads will that be an issue?

Thanks in advance for your help.

Silicon should not be conductive. After all, wafers are built up from silicon substrates.

20 white LEDs, @ 3.5V per LED = 70V
(120V-70V)/20mA = 2500 ohm

Is that what you were after?

Add a 1N4007 in series with the LEDs.
Calculations are using RMS, might want to use peak.
Use the correct wattage resistor.


Thanks when. I metered my LEDS and they came out at 2.5 volts but I trust your calculations better then mine.

better yet, buy some strings of white christmas tree LED's already strung and already designed for 120v

I had thought of that but the front face of material was laser beam cut with twenty holes just large enough to allow 3mm LEDs through. If the strand had more then twenty lights I could always just stuff them inside the present. I had also thought of drilling a hole in the side and wiring up a light socket for a standard bulb. But I wanted the individual pin points of light.

So I went with a remote controlled color changing self adhesive LED tape strip. I stuck it to the inside of the wooden box I made and just have the antenna that receives the remotes signals and the power cord coming out of the box.

Now I’m having a problem with soldering in my bigger wedding project. I pulled a fresh lead of wire off my roll. Then twisted a new LED out of the bag on the ends. I plug it in to the bread board on my test bed and run GoForSmokes sketch and wait. LED blinks yaa. Then I clip it in to my helping hands and solder it. Before putting the Heat shrink over the joint I plug it back in to the test bed. No blink no matter how long I wait.

The wire I’m using is solid with two separately sheathed strands one white one red. I’ve been careful with all my LEDs to solder all the whites wires on to the positive of the LED and the red wires on to the negative of the LED. I’m using silver bearing rosin cored solder that says it is for electrical. I’m doing my best to not get the soldering iron too close the LED. Any thoughts.

Figured out the photo uploading.

And the other two photos.