FreeTrack Forum

I'm in a very similar position to this poster http://forum.free-track.net/index.php?showtopic=4242&page=1 except I'm physically fit, but permantly house bound and need something to do with all my spare time.

I'm starting out with the same LED's as that poster for a USB build.

https://www.jaycar.com/productView.asp?SUBCATID=976&CATID=78&ID=ZD1945&URL=index
(5MM EMITTING DIODELooks like a 5mm LED & has a blue transparent lens.Specifications:- Forward Current (If): 50mA max - Peak forward current (Ip): 1.2A- Forward Voltage (VF): 1.2V @ 20mA - Reverse Voltage (VR): 5V max- Power Dissipation (Pd): 100mW max - Viewing Angle: 30°- Peak Spectral Wavelength(IR): 940nm @ 20mA * Spectral Bandwidth (DI): 50nm@20mA- Material: GaAs)

Want to add a PTC for MB protection and this is the closest one I can find available to me:
http://www.ebay.com.au/itm/60R010XU-Littelfuse-Polyfuse-Ptc-60R-Radial-0-1A-/131209401150?pt=AU_B_I_Electrical_Test_Equipment&hash=item1e8cb0933e
(Carrying Current Max:    40A
Holding Current:    100mA
Initial Resistance Max:    7.5ohm
Operating Voltage:    60V
PTC Fuse Case:    Radial Leaded
Series:    POLYFUSE 60R
Tripping Current:    200mA
Holding Current Max Ih:    100mA
MSL:    -
Operating Temperature Max:    85°C
Operating Temperature Min:    -40°C
Power Dissipation Pd:    0.38W
Trip Time:    4s)

Is that adaquate? Also following the maths above with it's resistance being about 7.5ohms I need another 20ohms worth in my resistor (aprox.) and while I have several 1/4w 5% carbon film resistors lying around the house from projects on musical equipment I don't have anything quite that high. Is it okay to stack several smaller resistors in series (likes two 8.2ohm and a 3.3ohm) to get in the right ballpark or will that cause other problems?

Thanks in advance.

Hi,

I do miss your first post, sorry for that.

With the specs you give I get:

Specifications:- Forward Current (If): 50mA max - Peak forward current (Ip): 1.2A- Forward Voltage (VF): 1.2V @ 20mA - Reverse Voltage (VR): 5V max- Power Dissipation (Pd): 100mW max - Viewing Angle: 30°- Peak Spectral Wavelength(IR): 940nm @ 20mA * Spectral Bandwidth (DI): 50nm@20mA- Material: GaAs)

R = ( 5V – 3 x 1.2V) / 30mA (anything between 20 and 50mA max)
R = 47 Ohm

...so look for 47 Ohm resistor or anything near, (39 or 56 without going under 30 Ohm at the risk of passing 50mA).

Forget the PTC and go for any 5v USB mobile charger. You can get them for 5 bucks if you haven't already one in the drawer. It's the best protection for your motherboard, because a PTC isn't really sure.

By mobile charger do you mean a power bank like this?
http://www.ebay.com/itm/2600mAh-Power-Bank-External-Battery-USB-Charger-For-iphone-HTC-Samsung-CR-/181393738451?pt=LH_DefaultDomain_2&var=&hash=item2a3be8cad3

That probably does work better for my purposes anyway since I use a wireless headset...

Okay so for the 47ohm resistor is this adaquate
http://www.jaycar.com.au/productView.asp?ID=RR2542 (47ohm 1 Watt 5% Carbon Film Resistor)
Or will I need to import a 1/4 Watt one?
Alternatively could I line up say 7 of these http://www.jaycar.com.au/productView.asp?ID=RR1522 (6R8ohm 1/4 Watt 5% Carbon Film)
for the same net effect?

I can't see this link because of legal restrictions in some countries, but it's ok.
Any 5V mobile USB charger is okay (Ipod, Samsung, Sony or whatever, go for a cheap one).

1W resistor is oversized, but if you have enough space in your mount it doesn't matter. 1/2 or 1/4 is quit enaugh and smaller.

And yes, you can line up resistors without any problems.