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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > Forward Voltage / Tracking issue

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justonce01	#1 30/09/2013 - 17h30 Top
Class : Apprenti Posts : 10 Registered on : 30/09/2013 Off line	This is really confusing for someone without any electronics knowledge. I want to use this LED, but I'm not sure what to put under forward voltage in the LED wizard. http://www.everlight.com/datasheets/IR323_H0_A_datasheet.pdf If I want to use 70mA (according to the datasheet the max current for this LED is 100mA), do I pick just a slightly lower value than the min. forward voltage value for 100mA? So, 1,3V? Edited by justonce01 on 13/11/2013 at 16h00.
Steph	#2 01/10/2013 - 10h39 Top
Class : Moderator Posts : 656 Registered on : 16/11/2007 Off line	Hi, put in 1.5V will be ok.
Stormrider	#3 01/10/2013 - 10h44 Top
Class : Légende du Forum Posts : 466 Registered on : 02/01/2013 Off line	the forward voltage is the voltage drop over the led.We use a resistor to limit the current. if you use a usb-poweradapter and you want to use 70mA in serie 3 point set-up (usb voltage -3xforward voltage leds)/ 0.07A= (5v-3x1,2)0,07=20 ohm that forward voltage of 1,2v is something I found http://nl.mouser.com/ProductDetail/Everlight/EL-IR323-H0-A/?qs=vs%252bWWTB4QKZIluvDWAfJQA== doorlaatspanning=forward voltage doorlaat stroom= forward current so you don't need the led wizzard, you can calculte it now yourself. If you are still confused, tell me what powersupply you have and I help you
justonce01	#4 01/10/2013 - 14h00 Top
Class : Apprenti Posts : 10 Registered on : 30/09/2013 Off line	I want to use it in a parallel 3 point set-up, running with two 1,2V rechargeable AA batteries (like THIS but with different LEDs). According to the wizard, if I use 1,2V as the forward voltage value, I need 15ohm resistors for 70mA. Even if I put 1,5V as the forward voltage, I get the same numbers (15ohm). Am I doing something wrong or will this work?
Stormrider	#5 03/10/2013 - 10h56 Top
Class : Légende du Forum Posts : 466 Registered on : 02/01/2013 Off line	for paralel you can calculate it like this: (powersupply voltage - forwar voltage led)/0,07A= resistor value (2,4V-1,5V)/0,07=12,85 ohm(make it 13 ohm) (2,4v-1,2v)/0,07=17,1 ohm If you should use a 15 ohm resistor and the the forward voltage is 1,2V you will have 80mA . firstI also used that calculator but I learned on this forum how to to calculate.The calculation I make have the same outcome as what I measure with my voltmetre. In your situation I should buy different values of resistors.To high resistor value make you leds to weak to track and to low may damage them. Resistors aren't that expensive.
justonce01	#6 03/10/2013 - 14h53 Top
Class : Apprenti Posts : 10 Registered on : 30/09/2013 Off line	Thanks for the help. I'll post the results once I build it.
justonce01	#7 13/11/2013 - 15h58 Top
Class : Apprenti Posts : 10 Registered on : 30/09/2013 Off line	I managed to find SFH 485p LEDs and that solved the problem. But now I ran into a new one. When I try to look down and to the side, the tracking messes up and starts moving on the X axis and applying non-existent roll movement. Single pitch and yaw movement gets tracked fine. Here's a GIF: Trying to do the thing mentioned above does this: Oh, and that only happens when I turn it to the right side. Looking left and down works fine (most of the time, but sometimes gets the same issue). Could it be related to my tracking device or my settings?
Steph	#8 13/11/2013 - 17h07 Top
Class : Moderator Posts : 656 Registered on : 16/11/2007 Off line	Are the distance between the two front LEDs are really 110mm (2x55mm)? This seems to be quit small. What can happens is that they overlapped, when turning your head especially when the webcam isn't centred in front of you. Try to see if you got the same behaviour when you increase the sensitivity on yaw and pitch, so that you do not need to turn your head so far like yo do now.
justonce01	#9 14/11/2013 - 17h52 Top
Class : Apprenti Posts : 10 Registered on : 30/09/2013 Off line	Increasing the pitch sensitivity fixed it. Yes, the distance is 5,5cm. Isn't that enough? Because I saw a lot of people making similar looking tracking devices, by just placing the LEDs on a baseball cap. This might seem like a silly question, but is there a guide on how to properly position the webcam and yourself? Part of my problem was the positioning of my tracking device (cap). I had to slightly tilt it up. I used to be sat like this: ... but I assume this is the proper and preferred way? Placing the webcam and tracking device on the same plane?
Stormrider	#10 15/11/2013 - 10h32 Top
Class : Légende du Forum Posts : 466 Registered on : 02/01/2013 Off line	This might seem like a silly question, but is there a guide on how to properly position the webcam and yourself? Part of my problem was the positioning of my tracking device (cap). Most people make mistake with filling in wrong dimensions and forget that they have to get used to ir-tracking.You found out yourself. Increasing the pitch sensitivity fixed it. You had to move your head to far to get movement with to little sensitivity. If the leds are to close to each other you wil see the dots melt together sometimes, which will cause strange behaviour with tracking.I use a cap-model with the leds just at 8cm.It is smaller then yours, but I don't have any problem with it.At greater distance probably I will get problems.So you see it is not so easy to say how to properly position the webcam and yourself, it depends on the situation. But if you always have the three green tacking dots(right corner) with all the movements of your head, filled in right dimensions, almost no jitter then there should not be any problem with your position.

FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > Forward Voltage / Tracking issue

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