Electronic Circuits and Projects Forum

You might want to look at the number of posts and rating the gent has before casting aspersions of valid contribution...

Back to task: at distance a simple linear repeater may suffer similar accuracy problems. May I suggest a simple encoding (74148s) then a display (7447s) of the number.

A uC would allow a deluxe answer: a 2.5 digit display of +/- 20, based on the 40 sensor array. Otherwise, the above would suffice...but either way you'll probably want to change 40 to either 32 or 64 <<<)))

P.S. In reading again, your issue will not be display for view. It'll be the scanner reception: I'd have the receivers look for a specific pulse rate as modulation. Trick will be rotational speed vs distance & maximum modulation rate. You may want to drastically reduce rotation speed for distance/accuracy.

P.P.S. there are Really reflective materials (3M highway grade stuff) that'll do Amazing things with an appropriate power beam.

Sorry OlPhart. With 13000 posts, I (incorrectly) assumed Sceadwian would have noticed the -CIRCUIT- emphasis I tried to convey. (Evidentally not well..) I specifically included the word 'please' to try to minimuse incorrect perception of any ill-will. I note that did not work.. A display of the number? I'm not all that electrically knowedgable, do you mean like a 7 segment led number display please? If so, that unfortunately defeats the intent of this project sorry.(Can elaborate if needed.) If not, could I please have some more explanation and a circuit diagram please? Thanks OlPhart.
PS: Thanks again OlPhart. Added note to my 1st post, and I would not think the frequency of the beam striking the receiver would have anything to do with its distance from the source?.

Ok, I'm smooth... I thought a number to read would be easier to interpret than a point on a scale at a distance. The bit about rotation vs distance and any kind of pulse frequency for recognition is based on simple geometry about how long a signal is over any given point at the given distance.

I'll 2nd the use of a higher power laser (careful there) and ultra-reflective strips. It's almost always easier/cheaper to centralize the power than distribute the sensor/receivers.

Another consideration: At a receiver/repeater, what kind of LED at what 1/2 beam angle and power consumption were you expecting to see at what distance?

In further review, (I)we need to see the map of optical power vs distances involved to better detail the problem. Angles, beam widths, and power are not trivial outdoors especially at distance (>100'). It's the main reason LED flashlights are no threat to deer shining...... (teehee) <<<)))

As the receiver has to detect tiny light pulses, you'd want to use a photodiode rather than phototransistor due to the response speed advantage. You'll also likely want to use a high-pass filter to remove the effect of ambient light (that's what C1 does in the attached circuit; I1 is the photodiode).

Have a look at the attached circuit and simulation for a circuit designed to receive laser pulses; the output is also a pulse, so you'll probably want to extend it before driving your indicator leds. R1 sets the sensitivity and working range. the pulse width in the simulation is for ~100' (very roughly) based on 100' * 500RPM --> 1700m/s & with a dot of 4mm, that's a pulse width of 2.3us.

If there's too many parts in that circuit (as you'll have to duplicate it for each LED), you may wish to look into using CMOS inverter gates as amps, which may give a usable result.

Originally Posted by Duggie

I'm not clever enough to know if that circuit will work

It works - real world - with a 10us laser pulse; I have tried it. The variables include the illumination brightness, and turn-on slope (due to the speed of the photodiode and of the rotating beam).

Originally Posted by Duggie

I'd love to get that out pulse to trigger an led illumination for about 2 seconds please?.

You can just poke a 555 timer after it for now for your bench test. Circuit attached (there are other ways of course)

Originally Posted by Duggie

What about a picaxe chip & program to handle part of this / multiple photodiodes?

You will still need the amplifier to be implemented for each photodiode; the extending of the pulses and controlling of the LEDs may be done by a microcontroller (possibly picaxe but I don't know).