FreeTrack Forum

Hi everyone.

This is my first post here. So, here it is:

I already buit a 3 IRs clip, using serie circuit. The only thing missing is the right resistor, but when I put my parameters at the LED Assembly Wizard calculator, it gives me only the resistor's value for a parallel array.

My doubt is: can I use the SAME resistor in my serie circuit? Or the value of the resistor changes due to be using a serie circuit?

I have this doubt because I'll be using only ONE resistor intead of THREE.

Thank you very much!

I am replying only because no one else has.  I am not that familiar with the resistor calculator you used.  But, I want to point out that you cannot just swap resistors between a parallel and series circuit.

Joe Dunfee

Hello!

Whats wrong with a parallel array? Just build it in a parallel way? Or are there special circumstances that you need a serial array?

Hi, just registered, and I apologize for the huge run on I'm about to give, but I am in class and wanna do this quicklike.

I have a 3 point led hat I just built in series with the recommended infrared LED's that alot of people use (forgot the number) and a 9v battery and a wii remote for a webcam.  I am currently using three 100 ohm resistors in parallel soldered together and putting that 3 resistor assembly in series with my led's.  That makes for one big ole 33 ohm resistor with a rediculous power rating (so it doesn't get too hot).  If you calculate the voltage and current going through each resistor, it comes to about 1.3-4 volts through each LED with 90 some odd mA.  Obviously well below the max reccomended of 3v and 100mA, but I find it sufficient for a 40 inch monitor sitting 5 ft away with a bright window (not direct sunlight, but enough to brightly light the room)behind me.

I figure the reason for using a series circuit rather than a parallel is actually a power saving one.  the calculator says for you to get one 62 ohm resistor in series with each LED, and each led-resistor combo is in parallel with each other.  That should get you 3 volts across and 96-98mA through each LED.  By having 100mA goin in parallel with each other, you have 300 mA going through the whole circuit which burns out a battery much faster than a series circuit which runs at 100mA.
Also consider the power dissappated by the resistors: if you have 3 volts across each LED with a 9 volt battery, that means 6 volts go across each resistor.  you have about 100mA going through each resistor-led combination.  That makes for .6 W of power dissappated through each resistor (that is enough to burn out the itty bitty resistors, and not to mention, even if you have a 1 W rated resistor, it is still wayyy hot).

EDIT: in short, use a 28-33 ohm resistor with at least 1 watt power rating or equivalent if you are going to do it in series.

My NiMH accumulator has 2400 mAh. My parallel setup with the IR LEDs running at approx. 75 mA x 3 needs 225 mA / h. So with fully charged accumulators I can use this setup approx. 10h.  Like a realtime flight from Frankfurt to New York in a flightsimulator

Just one question: How does the Voltage/brightness changes in a serial array from one LED to another?

Hello Ferujo, thanks for the tutorial at the Adrenaline forum.

as you can see, I have a few posts already on this forum... thats because I was planning to build a freetrack system for some time already, but only now, with your tutorial, I will be really doing it.

r0tty @ 02/06/2009 - 20h29 a dit:

Just one question: How does the Voltage/brightness changes in a serial array from one LED to another?

There is no difference, assuming that comparable resistances are used.  But, a general rule is that the lower the resistor value, the more efficient the circuit, in terms of power used.  You can just play around with the various options of series vs. parallel, different LED's, and different battery voltages, until you come up with the set up you are happy with.

Of course, sometimes it is just easier to follow someone else's design, and not worry much about it.

Joe Dunfee