| |
Using pointers (pun) from a previous post, I have been building a laser
for my robots. I used a miniature laser pointer from Sam Goody which
was only $10. The hardest part so far was chopping up the pointer to
get out the guts. It turned into a major piece of butchery with a hack
saw. The module will mount in a 2x3 stud brick with the brass case of the
diode itself sticking out a bit. The surface mount board is about the same
size as the diode brass housing. The whole thing is 5/16 inch wide
(very "Lego") and 1.25 inches long.
It runs on three batteries producing a total of about 4.5 volts. I
measured the output of the RCX ports and found them to be 7.8 volts.
I measured the current drain of the laser with its original batteries
and found it to be about 37.5 ma, so I selected a 100 ohm resistor.
The module has quite a few surface mount parts on a tiny attached board.
It is definately protected in a number of ways, including reverse polarity.
So I just unsoldered the switch with a very fine point iron and magnifier
lamp and replaced it with a 100 ohm resistor. I unsoldered the spring
and was left with two nice plated holes for the wires to the brick to
mount. Without fancy diodes it should just refuse to work if hooked up
backwards. Heaven knowns in fiddling with it I have powered it backwards
many times. If I had tried to start with a diode I would have blown things
for sure 10 times over. But these modules seem to assume people are going
to put the watch batteries in backwards 50% of the time. One could I suppose
mount two of these with different polarities to the same output and select
which one to power with the motor direction.
So far things appear to work. What is left is to mount the unit into a
brick. In truth, for $10, scrapping a laser pointer is definately the
way to go! Reverse voltage protection (apparently), all the photodiode
stabilizationfeedback circuitry, and even a microscopic pot to set the
voltage threshold.
The pointer produces an intense spot of red light. I found a cute heat
sink that exactly fits over the diode brass housing. Probably not required
but does make it look neater. I hope I do not break anything in the final
mounting, or immediately fry the diode when I try to power it with the
brick directly after making it "pretty".
Usual disclaimers about playing with laser pointers apply...
|
|
Message has 1 Reply:
 | | Re: Lego Laser
|
| (...) One thing to make sure of is that the RCX outputs are not constant. If you power the pbrick with external power it can shoot to over 9.5 volts. Something to keep in mind. Dean -- Coin-Op's For Sale!: (URL) Lego Workshop: (URL) Lego Club: (URL) (24 years ago, 12-Apr-00, to lugnet.robotics.rcx)
|
3 Messages in This Thread:
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
