FreeTrack Forum

Getting a new MS VX-1000 so now I'm going for the LED, resistors and soldering things.
I can not find it in the search topic but I was thinking why using 3 resistors and not 1 for a parallel system.
In http://ledcalc.com/#calc they are using 1 resistor???

Dutch

If you going to put LEDs together, you need one resistor for each circuit to limit the current.

Putting 3 LEDs in series means one circuit, one current and one resistor.

Putting 3 LEDs parallel means 3 independent circuits, so vou need 3 resistors to limit the current in each one of them.

ledcalc.com puts them im series, which is acceptable for this application.

The summary:

- you have one supply-voltage (Ug): e.g. 12V
- you can say, that on each diode the voltage falls constantly (Uf): e.g. 1.5V
- if you put diodes in series, you add each Uf
- you may reckon that a diode is a short circuit for the current: so you need resistors to limit the current at least to the maximum forward-current (If) specified by the manufacturer: e.g. 100mA
- knowing all that, you can calculate the resistor(s)

-> 3 diodes in series: R = (Ug-3*Uf)/Ig = (12V-4.5V)/0.1A = 75Ohm
-> 3 diodes parallel for each circuit: R = (Ug-Uf)/Ig = (12V-1.5V)/0.1A = 105Ohm

- here, the parallel order uses 3 times the current over the serial order and it is a tiny bit more demanding to build. This means if you plan to use some kind of battery-pack, stick to the serial order ;o)

If current matters, you don't need the full specified 100mA to get good tracking- results.
My Diodes for instance do the Job at about 40mA. Anything more just gets them warmer... of course you have to experience for yourself what your LEDs are capable of.


Sorry if I babble too much. I need to practice my technical english big time, so I keep on babbeling and hope to learn something while I'm at it ;o)

VG Gizzmo

thanks, but if you click "parallel" in LED calc you see 1 resistor for a parallel LED system (fill in number off LED's = 3).

So they using only 1 resistor for an parallel system, looks to me more simple to soldere then 3 resistors as calculated in this Forum's LED calculating system.

Dutch

Hupps, sorry. I didn't see that :o/

As far as I'm concerned this is not an appropriate way to wire LEDs.
You can do that if you're having 3 exact the same LEDs made from one and the same piece of silicon. Otherwise their characteristics may differ slightly form each other and 2 of the LEDs may be damaged or at least won't work properly.

Because you can never be sure about the characteristic curve of your LED unless you measured it, you're on the safe side NOT to connect your LEDs like that.

If you just want to use one resistor and save some energy: put them together in a serie.

VG Gizzmo

Yep so only different brand LED need seperated resisitors. Modern factories now a days are very good in their LED spec. so I take the risk and going for 1 resistor. M'n LED's are all from the same factory.
For the supply I'm using recharceble AA (1,2V 3A) or AAA (1,2V 1A) batteries, so duration is not the isue.

Dutch