[Laser] Ramsey kits for sale?

[Art]

At 11:32 PM 6/29/04, you wrote:
>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.


Hi James,

I looked up the 2n7000 mosfet on the Fairchild Semi site. Typical specs say 
it conducts fully with a gate voltage of 2.2 volts. Anything above that, 
and the transisitor should be full on. The device is good for 200 milliamps 
continuous and 500 ma pulsed-it should have more than enough current 
capacity to blow up any low power laser diode.

>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.

Once the device is on, it runs about 2 ohms resistance between the drain 
and source. Hence, the voltage drop across the fet should be about .1 volts 
(assuming a 50 ma laser current).

2N7000 specs at:

www.fairchildsemi.com/ds/2N%2F2N7000.pdf

>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.

Last night, I did find some info on laser sam's faq regarding drivers. He 
states that some low power laser diodes can safely be run using only a 
resistor to limit current because of new and improved manufacturing 
techniques. These devices are identified by the lack of a third lead since 
there is no photodiode required to sense power output of the laser. They 
still have widely varying power output as the temperature changes and they 
still need a good heat sink, but they can apparently stay within acceptable 
current limits due to the new manufacturing process used.

Regards,

Art