> Finding the right Resister for USB power IRLEDS
|
|
|
remoteplayer1 |
|
Class : Apprenti
Posts : 24
Registered on : 27/07/2008
Off line
|
thats what i am doing, black and red wires, no voltage at all. should i remove the data pins in the usb part that plugs into computer?
i am obviously using a breadboard to see if i wire it properly
|
|
tristan68 |
|
Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
Off line
|
Hello remoteplayer1
You can remove the data cable if you want , but don't ground them thats all
|
|
remoteplayer1 |
|
Class : Apprenti
Posts : 24
Registered on : 27/07/2008
Off line
|
ok i figured out why i was getting no voltage in the usb it was because the color code was wrong
another problem has arrissed though the 485p arn't lighting up when i test the setup on a bread board i am using a digital camera to try and see them.
are the polarities backwards on these or something, i am going to test it tommorow but i hope i dont burn them out.
|
|
tristan68 |
|
Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
Off line
|
Hello remoteplayer1
You can normally NOT destroy SFH485P with usb power by wiring them the wrong way, since their reverse voltage is 5v. So if you wire them the wring way, they'll simply not light up.....
You can still destroy them by overpowering them, so beware.
remember : these are IR leds, you should only see a VERY FAINT red glow on their chip when they are operating (almost nothing).....
cya
|
|
remoteplayer1 |
|
Class : Apprenti
Posts : 24
Registered on : 27/07/2008
Off line
|
it does the same thing with the wrong polarity. i put it corrdct and i just tested it right now with long being + short - and it doesnt do anything, its weird if i measure the voltage from the end of the resistor to the end i get 5 volts. and when i measure the voltage of the leds i get nothing. i am using the exact schemtics with ptc fuse> resisitor> leds
maybe the cameras digital cameras just aren't picking it up, how faint is this glow ? from peoples pics with 485ps they looks pretty bright to me
|
|
tristan68 |
|
Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
Off line
|
Hello remoteplayer1
Seems bad news to me.
Can you please confirm the setup you're currently using (since I re-read the complete thread, and now i'm unsure of the setting you finally used.
I apologize in advance , but just to be sure :
- To measure a voltage , you put the leads of your voltmeter on each side of the component you want to check , ok ?
So to measure the led voltage drop , you put the red wire on one side of the led, and the black wire on the other side of the led, ok ?
If you do so, and :
- read 5v when your check your resistor
- read 0v on the led monted in serial with that resistor
then it seems the led is short circuited.... eq fried...
please confirm me the whole thing :
- your current setup
- the voltage you get on each component, including the power source (power adapter or USB cable)
thx
|
|
remoteplayer1 |
|
Class : Apprenti
Posts : 24
Registered on : 27/07/2008
Off line
|
currently using the usb 5v, ptc 0.2a fuse, 20 ohms resistor, 3 leds setup
i reversed the polarities again and they seem to be working.
|
|
remoteplayer1 |
|
Class : Apprenti
Posts : 24
Registered on : 27/07/2008
Off line
|
added my hat to the point model gallery thread
|
|
Fanboy1337 |
|
Class : Apprenti
Posts : 22
Registered on : 03/04/2009
Off line
|
edit: never mind, sry  |
|
mattme |
|
Class : Apprenti
Posts : 1
Registered on : 24/03/2010
Off line
|
Ok I tried to my own hat rig to usb
I made my power cable like this
[usb +] ----->PTC (the spec'd above) -----> Resistor 10 Ohm 10% 1w -----> Led ----->Led -----> [usb -]
So in series would not light up but in parallel (one resistor before the parallel split) they would. Any thoughts is the resistor to blame. Is the fuse and/or resistor directional?
THanks
Matt
The led x 3 are the sfh 485 p
PTC Fuse: FUSE PTC RESETTABLE .1A HOLD
Resistor: Brown. black, black, silver
|
|
buccaneer |
|
Class : Apprenti
Posts : 24
Registered on : 14/03/2010
Off line
|
mattme @ 02/04/2010 - 04h47 a dit:
...
[usb +] ----->PTC (the spec'd above) -----> Resistor 10 Ohm 10% 1w -----> Led ----->Led -----> [usb -]
...
PTC Fuse: FUSE PTC RESETTABLE .1A HOLD
Resistor: Brown. black, black, silver
Do you really have 2 LEDs in serial layout(as you show in diagram)?
If you have only 2 LEDs, than you will have 5 - 1.5x2 = 2V voltage drop on the resistor.
The current will be 2V/10Ohm = 200mA and with PTC with hold at 0.1A it will be close to trip(block) state. Do you use PTC in parallel wiring also?
AFAIK resistor and PTC are not directional
|