wire in an led indicator light

[smoothcannibal]

starting a tube mod project in the next day or so when i get to the hardware store to pick up the rest of the bits i need. going to make a few to give my wife and other family members if mine works good. i might make some for my moms plant sale in the spring to sell as i have a couple ideas that i haven't seen that could set me apart.


i would like to add an led for an indicator that it is firing.

i tried searching and all i could find was the box mod tutorial from madvapes. but i am using the body for the negative connection


can i just solder both connections of the led in with the positive wire or do i need to connect one to the body to act as a negative. does it matter if its between the atty connection and the switch or between the switch and positive batt connection.
do i really need the resistor that came with the led?

all my soldering/electrical knowledge comes from my tamiya/traxxas rc habit, but i'd rather ask since if not done right can be dangerous. and this is a little different than servos and speed controllers etc.

 

[asdaq]

Yes you do need a resistor, and here is why:

If the voltage is too high the current will go above the maximum rating, heating and potentially destroying the LED.

If the supply voltage is equal to the LED's voltage drop, no resistor is needed.

Typically a LED will be rated for about 3v, and we supply 3.2-4.2v with a single Li-On or more even with electronics added to the circuit. You likely have a 470ohm resistor that goes with it, this is fine for a LED sticking out of a mod, if you want it brighter you can go down to about 100ohms. The resistor may be connected to either the positive or negative leg of the LED, it limits either way.

 

[Seebs]

The resistance rating for the little resistor you want to add will vary depending on three things:

1 Supply voltage: If the tube-mod you're making is going to be a single voltage thing (3.7V Set it and forget it) type. Then that 3.7V is your supply voltage.

2 Forward Voltage also known as LED voltage drop.

3 Forward Current also known as LED max current.

Let's take this LED for example: 3mm RED LED standard - 1.8 - 2.2 forward voltage - 20mA

You would go to any online LED resistor calculator; I like this one: ledcalc and plug in the numbers on the LED you plan on using.

If we use that calculator and input the numbers on the example LED I linked to; we get:

Supply Voltage: 3.7V
Voltage Drop Across LED: 2.2V --> Notice that the LED we picked shows a range between 1.8V and 2.2V for the voltage drop. Entering a lower number in the range for the voltage drop will mean that you use a higher rating resistor. I always go with the high end of the voltage drop range and call it a day.

Desired LED current: 20mA as stated by the LED specs.

Number of LEDS: 1 -> Unless you want more than 1 LED in there.

And then you hit the "Calculate" button. The page will give you the exact Ohms you need for the LED. In this particular case; it results in an exact resistance of 75 Ohms, but resistors on 75 Ohms are not made so you have to get the next one up. In this case; it shows you that you need to get the 82 Ohm resistor and it needs to be rated for at least 1/8 watt.

Once you have all the numbers; it's just as easy as soldering the the positive leg of the LED (Anode) - That is the longer leg - to the (+) line on your mod... And the negative leg of the LED (Kathode) - The shorter leg - to the (-) - GND side of your mod.... That's it... Easy as pie once you get it figured out.

If you feel like doing the math yourself; the formula to calculate the required resistance for any give LED is:

R = (V_S - V_L) / I

R -> Resistance
V_S -> Supply Voltage
V_L -> Forward Voltage
I -> Forward Current.

Hope this helps

Seebs

 

[asdaq]

1 Supply voltage: If the tube-mod you're making is going to be a single voltage thing (3.7V Set it and forget it) type. Then that 3.7V is your supply voltage.

Uhh, Seebs, fresh off the charger it is much more like 4.2v. That is why I suggested a 100ohm minimum.

 

[Seebs]

Uhh, Seebs, fresh off the charger it is much more like 4.2v. That is why I suggested a 100ohm minimum.

LOL... Goes to show. I'm not as much a noob at LEDs and wiring electronics as I am about PV mods.

In that case; I'd say go with the 100 Ohm resistor.

 

[smoothcannibal]

i should have mentioned that they will be 3.7v mods using single 18xxx batts. i got the 3mm green led from madvapes with a 470 ohm resistor. i figured i did need the resistor but you never know. i will be stopping off at radio shack for a different resistor.

so from what i am getting is, solder the negative leg of the led to the body and the positive to wire leading to the battery with the resistor on either side.

thanks guys.

 

[asdaq]

That 470 ohm resistor will work fine too, it just won't be as bright. If you are building a mod that the LED sticks out a bit and you just look at it to see that it is on, it may be just what you want. You can literally hold the parts together and to a battery to see if it is enough. For a brighter LED to illuminate a tank or similar then a 100 or 200 ohm may be in order. You probably don't want it to light up your nose or blind you though.

 

[daPorkchop]

You probably don't want it to light up your nose or blind you though.

I'd buy that mod! Except the whole going blind thing...