Getting the most from an LED
Hi guys. I have recently written the walkthorugh on how to transmit serial data with an IR led and it works fine. Now to the next step: i want to achieve the highest range possible with my LED, without using external aids such as lenses. (that is: only with electronics).
I have a TSAL 6100 from Vishay ( http://www.farnell.com/datasheets/93358.pdf ). If I am right, to achieve the most out of it, i have to get a current similar to the "peak current" value from the manual in the LED. But as for the voltage i guess i just need to give it at least a value equal to its forward voltage.
Problem is, i am not sure about the things i have just written... :) Is it really the right way to do it?
Suppose it is, i cannot give enough current to the LED with an output pin, so i think i'll be using either a mosfet or a standard NPN. But again, how do i exactly know what current i will get with it? As far as i know i have to measure the "amplification value"( hFe?) with my multimeter and multiply that to the current entering the base. Am I right?
@ Tue, 2008-12-16 22:35
back on the topic!i need to
back on the topic!
i need to get a mosfet for the IR LED circuit. The above circuit suggests this one: http://www.irf.com/product-info/datasheets/data/irld110pbf.pdf
Could you just give me a brief explanation of its features?
For example :
what are these two things ( i suppose the first stand for the maximum voltage the drain can pass to the source, but don't have many clues on the continuous drain )? Is there an internet site that explains these kind of things so that i don't have to bother you every time? :=)
@ Tue, 2008-12-16 23:41
Parameters
@ Mon, 2008-11-24 15:46
it is strange though....look
it is strange though....look at the resistance values at the top left, they're really low ( i guess they are the ones to be used with the IR LED), considering we came up with a max value of 200mA at 38kHz and 50% duty cycle and he has a min of 347mA and 56kHz (without considering the use of power mosfets).
These things make me wonder...
@ Mon, 2008-11-24 18:07
Why wonder?
Remember that the IR LED datasheet had a max of 200 mA at a rate of 5000 Hz, 50% duty, repeated ad infinitum. The next parameter down is a non-repetitive surge current of up to 1.5 A for a similar 100 uS as before, but not repeated. The LED won't just immediately fry if going above the 200 mA, but this is a point in a curve of what it can take for an extended period of time. The other circuit shown is probably estimating some cool-down time for the LED to rest when it is not being driven, and tried different values to get even more current through it, without burning it up. And the FETs were probably used to get the currents greater than 350 or 400 mA, about the limit of many basic BJTs. I think 2N2222 BJTs can go up to 500 mA pretty easy, but getting much higher would require the FETs or stronger BJTs in a different package (TO220).
THe kHz is probably to match the detectors they are using, different TSOPs.
@ Mon, 2008-11-24 18:20
yeah, no worries about the
yeah, no worries about the KHz. But no, it is not expecting any cooldown time. As it says in the protocol page, the system can "shoot" up to 29 times per second, and that is sending 16 data bits continuously. But then he clearly states "[...]as the limits of the Infrared LED are often stressed in Laser Tag designs to gain maximum power and range."
I guess that in these cases you just have to use a bit of common sense. You won't be keeping your finger on the trigger for more than a sec anyways, so at most you'll just stress the LED a little more than you should and substitute it in case it burns out.
@ Mon, 2008-11-24 19:17
Dividing a second
@ Sun, 2008-11-23 23:02
i've found this schematic.
i've found this schematic. It was taken from lasertagparts.com, and wants to do a similar thing, well, actually it is exactly the same, as we are trying to do.
here it is:
question is: why is he using Power Mosfets, or well, let's say field-effect transistors in general, instead of standar bipolar transistors like i am using? Is there something to gain?
@ Mon, 2008-11-24 00:19
FETs and BJTs
@ Wed, 2008-11-19 21:49
It works! The problem i had
It works! The problem i had was related to..well...misreading of the datasheet, i thought the collector was on pin 2 whereas it was on pin 1...
Anyways, i've used the schematic of the AND gate with transistor and placed my resistor and IR led on its output (on the output of the AND gate) and it works. As for the coding I used T (true) reception on the receiver and it works (notice that i kept N on the sender).
how cool :)
@ Thu, 2008-11-20 00:51
Way cool!