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viper3two #1 12/12/2007 - 12h35

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Hello, sorry if I got this wrong but could interperet the french posting buttons, hope this works.
I have and understand the webcam removal of IR filter and adding a negative film for filtering. All ok there.
I am planning on making a 3 point clip for a cap. I have ordered 10 of the recommended LED SFH845P, incase I mess it up I will have spares.
I will be using the series-type wiring schematic. The problem I have is I am unable to use the calculator to determine the resistor.
First, what is the recommended ma of the 3 point clip for the power supply? I plan on using a power supply instead of batteries. It will be 6 volts (same as 4 1.5 batteries), but I do not know whether to get a 300ma or 500ma power supply.

The second question is what resistor should I use if I plan on getting a 300ma power supply, or the 500ma power supply, could you list both recommendations.

thank you
viper3two
Kestrel #2 12/12/2007 - 12h52

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viper3two @ 12/12/2007 - 13h35 a dit:


First, what is the recommended ma of the 3 point clip for the power supply? I plan on using a power supply instead of batteries. It will be 6 volts (same as 4 1.5 batteries), but I do not know whether to get a 300ma or 500ma power supply.

The second question is what resistor should I use if I plan on getting a 300ma power supply, or the 500ma power supply, could you list both recommendations.



A power supply is normally a constant voltage source that supplies whatever current the circuit wants, up to a maximum value. The 300mA and 500mA values you mention are the maximum currents that those supplies can provide and since LEDs normally require less than 100mA, there's no practical difference between the two supplies.

The current (mA) that you enter into the wizard is the LED current and needs to be less than the maximum current as per the specifications (100mA in the case of SFH385P). Try 40mA.
viper3two #3 12/12/2007 - 23h52

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First, thank you for the reply. I think it is beginning to make sense. So each LED have a max current of 100ma, so the resistor needs to knock the power down to keep from reaching the max, so in this case you say I could use a 300ma power constant voltage, and use a 40ma resistor to keep the current (ma) from reaching the max.
In this case I would need to buy a 300ma power supply, 6 volt dc and a 40ma resistor. Correct?
One other question is MA the same as OHM? I think when I was looking earlier it listed some resistors at a local store as for example 40Ohm. Just wanted to be sure that is correct so I can order the right stuff.
Thank you again, excuse my electrical ignorance here -)
Kestrel #4 13/12/2007 - 00h19

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They're two different things:

mA = milliamperes: measure of current flow
ohm: measure of resistance to current flow

You just put 6V, 1.5V and 40mA (the latter two being the SFH485P characteristics) in that order into the LED assembly wizard and it will give you the required resistance.

Which is 39 ohms for a series circuit. (I had to use the assembly wizard on the french site because the english site version only outputs a parallel circuit)
viper3two #5 13/12/2007 - 11h49

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Thanks again Kestrel. Now it is all making sense! I went ahead and ordered the items last night on line, should have it here end of next week sometime. Can't wait to get this little project underway, been wanting a TrackIR for sometime.....
Appreciate your time and patience with me.
viper3two

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