[Laser] Ramsey kits for sale?

[TWOSIG at aol.com]

Art

My units are not for sale, but I think that I can help you with the 
transmitter problem.  In simple terms the Ramsey driver circuit is +5 volts to the 
laser pointer that is designed for 4.5 volts out of watch batteries (that don't 
supply much current).  The switching device is a 2N7000 FET which connects the 
pointer to ground when the gate is driven by the microprocessor.  

Two things could be wrong.  If the +5 volt regulator is not holding the power 
line down, the rest of the circuits shouldn't fail, but there is nothing to 
prevent the current from zapping the laser pointer.  If the supply is a firm +5 
volts, then the FET, which is supposed to drop at least a half volt, may be 
running with too low a voltage drop.

I have run both of my transmitters, with +12 volts supplied to the voltage 
regulator, continuously for more than 5 hours at a school demonstration with no 
problems.  My units use the stock components and stock circuit, although I did 
modify the mechanical details.

If you try to soup up the output, my advice is that you put a 1K resistor 
from +5 to the top of the FET and build an outboard laser driver circuit that 
limits the laser drive current to a safe value.  The driver circuit should be 
turned on by the FET going low, about 0.5 volt, and sinking no more than 20 
milliamp.

Hope that helps.

James
N5GUI

In a message dated 6/29/2004 7:34:21 PM Central Standard Time, ky1k at pivot.net 
writes:



Hi Everyone,

OK.

Al, XE2AT has modified his Ramsey laser communicators for use with the Burr 
Brown opt-101 receiver chips. He says the boost in receiver sensitivity is 
very substantial, his receent 25.8 km laser QSO was made possible due to 
the improved sensitivity of the mod. A previous attempt at the same 
distance with the stock receiver did not succeed..

But, he has blown up laser pointers, now he has a pile of 4 bad lasers. 
Presumably this is due to the simple driver (just a current limiting 
resistor). I'm looking for a replacement for him, something that can be 
bolted in and run properly. Hopefully this will provide a little more power 
and have a proper photodiode based APC control so that the lasers won't 
continue to blow.

It's really tough to hack on these things by long distance however, linked 
only by email.

Does anyone have a pair of the Ramsey Laser Communicators for sale at a 
reasonable price???? Please advise if you are willing to part with your 
Ramsey's. I want a complete set of transmitters and receivers (2 of each).

I also have a pdf documenting the mod to put the opt-101 integrated 
photodiode and amp into the Ramsey receiver. Al says it works much better, 
I only have his word regarding the success of this as I haven't tested it 
myself. Any, I am happy to email the pdf to anyone who is interested in 
hopping up the Ramsey receivers.

Regards,

Art


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