Chris writes – “P.O. sent us this how-to on building a very handy flashlight out of a old TicTac mint box. It consists of a empty TicTac box (duh!), three batteries (that fits perfect), a small switch, a resistor and a bright LED. It might not take a rocket scientist to figure out how to connect it all, but still…” – Link.
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10 thoughts on “HOW TO – Make a TicTac flashlight”
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Am I the only one incredibly annoyed by comments like “an ultra bright white LED (25.000 mcd – 3,8 volt and 20 mA – 35 degrees) and a serial resistor of 27 ohm (to make it 3,8 Volt).“?
It seems like most people using LEDs have no clue what they are doing or why they include a resistor.
Well, according to my calculations, given a 4.5V source looks like he would be overdriving it at around 26ma instead of 20ma. The LED will burn out quicker than if he used a proper resistance which should be about 35ohm, but it might still last a decent time.
Here’s a good resistance calculator:
http://led.linear1.org/1led.wiz
I wasn’t so much commenting on his choice of resistor value. I’d probably go with 30mA for a flashlight like his design that’s only meant to be used in brief bursts.
What I’m talking about is thinks he’s using the resistor to “make it 3.8 volts”. The LED will drop 3.8 volts (if that’s the rated value) for any supply voltage greater than 3.8 volts. The resistor is what limits the current through the LED.
It annoys me that I keep seeing crap like that post over and over because people read postings like it and believe it and then post their own version.
Could someone who knows the connection pattern for the parts, or can guess it, post a how to for those of us who aren’t smart?
It doesn’t really matter that people don’t understand quite why they are doing something on a project this small, but once they get onto something bigger, which switches and transistors, they will be in trouble.
The resistor is there, as Oracle points out correctly, to limit the current across the light emitting DIODE junction. It has nothing to do with the voltage! It’s a non-linear device, and so trying to look at it from a voltage point of view is seriously flawed.
I should just point out that the LEDs here are probably rated to 100mA for short periods, so short uses (a few seconds or so) at 50mA won’t kill the device instantly. In fact, it will give more light, but for a far, far shorter time, and perhaps kill the LEDs in a week, rather than 20 years. YMMV.