FreeTrack Forum

Do I need to use a resistor if I use 3 x AA batteries (4.5v), I think the SFH485P are 1.5v each... is that right?. My webcam has a floppy disc IR filter.

If I go with a rectangular 9v battery, what resistor do I use?

Please let me know if you have any tips on what battery/resistor combination is best & will last the longest amount of time.

Cheers
Al

Hi

Check this out http://www.free-track.net/english/hardware/calcled/

is a link on the main page of Free-Track, just fill the values and it will tell you the resistors you need and how to connect the leds... pay special attention to "Dissipated power" value cause it will tell you the wattage that the resistor needs to handle...

In my case i'm using a 9v battery with 2 watts resistors, but i´m not using SFH485P leds

Regards

I'm not an expert so i don't now exact reason but it's adviced on the internet to always use resistors with leds

In my opinion you should first think about the battery life. AA holds something like 2200mAh, AAA 850 mAh and 9V 270-500 mAh. If you connect two batteries in parallel your mAh will double and if in series your voltage will double(mAh stays the same).

Depending on your setup(ir filter, visible light filter etc.) your leds need 3 x 30-90mA = overall 90-270 mA. So you can calculate battery life easily... For example one AAA gives something like 850mAh so with two AAA's in series you get overall battery life of 850mAh / ( 3*70mA ) = 4 hours and voltage of 3V.

You can connect led in parallel or series. If parallel: voltage needed for 3 leds is 1.5V and if series 3x1.5V=4.5V. Basically you will have to think what kind of battery life you will need/want and how big batteries you want to install to your 3 point setup. Rechargeable batteries are an option but remember that the voltage is a bit smaller(1,2V per battery). When you have made a decision use that calcled to calculate proper resistors for your wanted mA per led.

Ps. I'm not really an expert on this but wanted to answer because this forum is quite dead. If someone notices an error please correct.

Pps. My model is in prototype-stage. I ended up using a separate 6V regulated power supply, 30mA current(ir filter removed and visible light filter installed). Prototype seemed to work fine now I just have to think the final design through and find the time and motivation to make the final version =)