Newbie needs help with first circuit

[Ragerin]

Hello all.

 

 

First of all - I am getting very inspired by all the amazing home cockpits in here. I really hope to be able to make something like them, one day.

 

 

As I want to get started learning, I chose a simple, first project. :smartass:

 

The deal is, I find the TrackClip Pro very fragile and I fear, that some day it will break! And there's just no way, that I could be without it. Heh.

So I wanted to create my own TrackClip, from some more sturdy materials (maybe some lightweight metal or something...). But I never did any electronics before, so I would very much like some advice.

 

 

A (crude) image is attached of my idea. Sorry for using homemade symbols - I have never done anything with circuits before.

Also, a link to the data sheet of the IR LED's is below.

 

 

I am thinking of using a USB-cable for power (just like the original TrackClip Pro). This gives me an output of 5 V.

 

The IR LEDs I've found, have a forward voltage of 1.5V and a forward current of 100mA.

They also have something listed as an "Off voltage" for 5V. What does this mean?

 

 

So now my question is, what do I need to get for a resistor?

I tried using this calculator:

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

But I don't know if I used it right. I put these numbers in:

Supply voltage: 5V

Voltage drop per LED: 1.5V

Desired LED Current: 15mA

Number of LEDs: 3

 

Based on the results, I have been looking at this resistor:

ACS5S 39R J TR

Resistance: 39 Ohm

Rated effect: 5 W

Tolerance: +/-5 %

 

Can I use this one? Or do I need another resistor?

 

 

Link to data sheet of IR LEDs: https://www1.elfa.se/data1/wwwroot/assets/datasheets/efSFH487P_data_de-en.pdf

 

 

:helpsmilie:

 

I hope somebody can help me, so I can learn how to do this in the future.

 

Also, I apologize for my english, it is not the best. :music_whistling:

 

 

Sincerely,

Ragerin

[geert]

Hi,

 

There's someone on ebay how sells an alternative to the track clip pro, search for "Delan" or "delan clip" or something on ebay and/or on this forum for more info. He also sells the separate parts so you can do your own assembling. Can't really help you with the electronics stuff, there's other people in here who can I'm sure.

 

cheers,

Geert

[Ragerin]

Hey geert.

 

Thanks for your reply. Yeah, I saw that "DelanClip", which is in fact another inspiration for me. :-) I hope that I can learn to choose the bits and pieces myself and do the necessary calculations. But thanks any way! Definately a solution.

[Boltz]

Ragerin that resistor looks fine. Use the formula R(Resistance)=V(Voltage)/I(Current). Voltage in a series circuit, which this is, is calculated by taking your supply voltage (5v but you can only get multiples of 1.5v in standard batteries) and subtracting the forward voltage (voltage drop) of your LED (1.5v.) In this case you have three LEDs so take the 1.5v off three times. This leaves you with a calculation of R=5-(1.5*3)/0.015=34 Ohms Resistance. The 0.015 is the forward current in Amperes (15mA=0.015A).

 

Look for a resistor of at least 34 Ohms and you should get what you want. I have based these calculations of of the numbers you entered into the calculator. This should show a breakdown of what it did but I don't see why it gave you 39 Ohms. That must be a standard resistor. Those IR LEDs show a forward current of up to 100mA so for increased brightness you could increase to around 80mA due to the tolerance of resistors i.e. they are not perfect and the percentage of tolerance is how accurate they are so a 100 Ohm resistor with +/-5% could range from 95-105 Ohms. Always assume it will be the lower number (which could be why the calculator got 39 Ohms) but as long as you aim for a sensible proportional current less than the forward Voltage (IF) you should be fine.

 

That probably wasn't the best way to explain it so you can do a search on google for more information but thats the basics.

 

Hope it helps,

Boltz

[Ragerin]

Hey Boltz.

 

Thank you very much. It was very clarifying.

 

So based on my IR LEDs, which allows for up to 100mA forward current - the calculator website gives me a safe resistance value of 6.25 Ohm (when I input 80mA as you said). So I would for 15mA need another resistor.

 

What do you think? Should I go for 15mA for the LEDs or should I yank them up to 80? Would the higher mA-value allow the TrackIR to better filter out the LEDs in contrast to ie. background lighting?

 

 

P.S. What do I do about fuses? I don't want to fry my motherboard, because of any newbie soldering. :-) Should I go for a PTC?

[Boltz]

I dont have a TrackIR so I don't know the necessary brightness but I would imagine that them being brighter does increase the contrast and so makes it easier for them to be picked out. Those have a forward voltage of 1.5v so three in series require 4.5v. If you give them exactly 4.5v (3x 'AA' or 'AAA' size batteries) then they will draw what they require and you will not need any resistor or fuses. If you give them the exact forward voltage they need then you don't require any additional circuitry. I don't have an accxount on any image hosting websites so I can't show you a diagram but three normal batteries in series connected to three IR LEDs in series will work. Try not to use rechargeable ones though as their voltage seems to vary a lot more from standard ones. Even better is to get a power supply that you plug into the wall that will provide 4.5v.

[Thick8]

This is a great tool to fill in your diagram's ?

 

http://led.linear1.org/led.wiz

 

The forward voltage and current is printed on the bag of the IR LED's that you can buy at Radioshack or wherever you plan on buying them.

Edited November 2, 2013 by Thick8

[Ragerin]

Thank you for your help! I think I have collected enough courage to try to make something. I've got a friend, who wants to help me with making the "chassis"/clip. He can make them in light metals and hard plastic.

 

I will upload some pictures, during and finishing the project, to show anybody interested how it works out. :-) I have my fingers crossed. Hopefully before Christmas, it will be done and I have a more stable TrackClip.

[Boltz]

Good luck. I am looking for some head tracking system at the moment. Probably going to try FreeTrack so I will need to build one of these as well.

[Ragerin]

I have sent you a friend-request, Boltz. Perhaps we can inspire each other. :-) Hope to hear about your ideas.

[Boltz]

Accepted it. Will be good to see some pictures of what you come up with.