ee8kh@gdt.bath.ac.uk (K House) (03/06/91)
I'm currently undertaking a small project using Infra-red LEDs to transmit information over distances of about 50 metres (through air). However, the range I am currently achieving is not really high enough for the application I have in mind and so I am toying with the idea of using laser diodes as emitters instead of the diodes I am using at present. My current two emitters are a CQX19 and a (TW?)5202 both being driven by pulse currents of about 8amps for a couple of microseconds at a repetition rate of about 60kHz. With either of these two diodes I can achieve distances of 50metres or so, but I am aiming to achieve at least 200metres. (I cannot easily make any changes to the sensor, so I need to improve the emitter). To get to the point, can anybody out there tell me where I can find out about infra-red laser diodes and their transmission distances esp. w.r.t. power output The only laser-diodes I have found so far are 10mW, which I think is far too high an output to be eye-safe (another very important requirement). Please bear in mind that I intend to collimate(sp?) the beam to a spread angle of less than 1 degree. What level of power output is acceptable, for how long, what duty factor etc.... ? I am currently using a converging lens to try to narrow the beam-spread, can anybody tell me how much more effective a proper collimater would be, or where I might get one ? (my budget is very limited). In addition, any information regarding low power visible lasers (also eye-safe) would be greatly appreciated. I will gladly offer further details of the problem if required, just drop me an email note. Thanks in advance for any help you may be able to offer. Kevin House -- " If I was someone, I would like to be the fool. ___ No-one would know me and I think that would be cool. " / / )__ __ ^__ __ __-_This_Mortal_Coil ______________________________________/ / ((_(( (((_((_.__
larry@kitty.UUCP (Larry Lippman) (03/07/91)
In article <1991Mar5.164506.18567@gdt.bath.ac.uk> ee8kh@gdt.bath.ac.uk (K House) writes: >I'm currently undertaking a small project using Infra-red LEDs to transmit >information over distances of about 50 metres (through air). >However, the range I am currently achieving is not really high enough for the >application I have in mind and so I am toying with the idea of using laser >diodes as emitters instead of the diodes I am using at present. I don't believe it is necessary to utilize laser diodes to achieve greater range, which later in your article you state is 200 meters. One of the simplest techniques in extending range to 200 meters (which is about the limit, btw) is to use multiple IR-emitting diodes in an array. Since multiple IR-emitting diodes cost less than an IR laser diode, this should be an attractive alternative. A second technique is to use a suitable IR filter material for the photodiode receiver. Failure to filter light below 800 nm will result in serious limitations to amplification of photodiode signals since its input will be significantly loaded by ambient lighting - especially that of fluorescent illumination. Many fluorescent lighting systems produce a really ugly 120 Hz signal with many higher frequency components because it is not a sine wave due to ballast characteristics. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry
wolfgang@wsrcc.com (Wolfgang S. Rupprecht) (03/10/91)
In article <1991Mar5.164506.18567@gdt.bath.ac.uk> ee8kh@gdt.bath.ac.uk (K House) writes: >I'm currently undertaking a small project using Infra-red LEDs to transmit >information over distances of about 50 metres (through air). >However, the range I am currently achieving is not really high enough for the >application I have in mind and so I am toying with the idea of using laser >diodes as emitters instead of the diodes I am using at present. If you just want to carry audio freq stuff you can also try a plain old flashlight bulb. Just bias it to the normal operating voltage, and then modulate it with the signal from there. The purist will notice that this is non-linear as all heck. True. Just keep the modulation to low levels. One 6" reflector, and a 3 watt bulb, for the xmitter, and a 5 mm^2 photodiode, a 3" lens, and a 536 fet op amp for the receiver will allow you to send telephone quality sound several hundred meters. -wolfgang -- Wolfgang Rupprecht wolfgang@wsrcc.com (or) uunet!wsrcc!wolfgang Snail Mail Address: Box 6524, Alexandria, VA 22306-0524