Rotary Laser level detector / receiver please

[Duggie]

Hi.
I'm chasing a --CIRCUIT-- design to make a laser level receiver please.
It'll be about a foot high, with maybe 40 vertical LEDs. I'd like ONE of those LEDs to light up when the photo-diode(?) beside it detects the laser beam, thus showing me where on the detector the laser is striking. The laser level rotates at about 500rpm, I assume the detector circuit will have to detect this faint laser pulsing differentiating it form ambient light readings? I'm not too bright, but keen for some help please?

The receiver will be in bright daylight, and will need to be seen from some distance, hence the interest in LED illumination.
I have appreciated numerous ideas offered, but unfortunately nothing has been a better solution for my application than singular led illumination, in a vertical column, about 250-300mm tall. From previous enquiries, It would also seem a successful circuit might relate to the cyclic pulse of the laser beam striking the detector cells, identifying it from the incoming bright ambient light.

This is not a new idea. These rotating lasers already have receviers/detectors that accurately read the beam from 100m or more away, with an accuracy of 5mm or less.
The problem is, the hand helds have a small detection height (2 inches or so) and usually offer a readout of high, on grade, or low. I wish to make a big one, that can been seen from a distance, that shows exactly where the beam is striking it, so I can see exactly how far off grade I am, from a distance, outside, in daylight.
Thanks.

 

[Sceadwian]

Why do you want to obfuscate the problem and not use a laser with a line generator that's visible to the human eye?

 

[Duggie]

The receiver will be in locations not close to a human eye. The LED illumination will be easier to notice clearly and quickly from distances, in daylight. The project is for earthworks. So your unable to assist with a circuit then I assume please?

 

[OlPhart]

Think it through...

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.

 

[Duggie]

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?.

 

[OlPhart]

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) <<<)))

 

[Duggie]

From my experience, analogue displays are subliminally easier to quickly mentally register than digital readout. Hence my desire for one of 30 LEDS to illuminate than to read a led numeric display. The present detectors produce an accuracy of abt 3mm over 300', so there's a chance the beam stays tight / narrow over that distance. No, it is not definite, the existing circuitry might detect on 3 cells, then average out to the middle one.. I already have the laser. Just wish to make a bigger receiver. Not sure where a repeater comes into it. The trouble I seem to be having is not many in the electronics forums understand what a rotary laser level is. Laser beam shines vertical out of level, rotating mirror above it spins the beam horizontally 360 degrees, abt 400-500 rpm. That produces a virtual level plane, NOT changing height. Somewhere off in the field you raise and lower a detector, when it says on grade, you measure down from there to ground to compare your ground height reading to that of the virtual level plane. I was assuming if laser was spinning at 500rpm, detector would be detecting a pulse hitting it at 500 times / sec 3' away from level, and 500 times / sec 300' away from level. The Leds can be shadowed into recesses to make them a little more noticeable in the daylight, I'd like to see them lit up from maybe 100'. In my experience, if my kids shine their led torch at me 300' away in the day outside, I can see when it is on, or off. No, it won't help me read a newspaper in the dark at that distance, but I'll see its on looking at it.. If I can invest the time, I should make a drawing to better explain.

 

[dougy83]

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.

 

[Duggie]

I'm not clever enough to know if that circuit will work, but it seems to be the best response to my enquiry to date BY FAR.
Extremely appreciated! I'd love to get that out pulse to trigger an led illumination for about 2 seconds please?.
If I can get the just mentioned led action, I could make one of these, turn it on, and 'swipe' it past my spinning laser and see if it works.
I have circuit wizard to emmulate it, but I don't know how I'd simulate the laser pulses into the photodiode..
Again, I'd like to offer my sincere appreciation for your circuit, its what I've been hoping for for a long time.
What about a picaxe chip & program to handle part of this / multiple photodiodes?

 

[dougy83]

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).

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)

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).

 

[Duggie]

Please pardon my stupidity, but, Vce =5v? Pin 6 Earthed throught the 1Meg resistor please? Pin 3 to LED then ground?

 

[KeepItSimpleStupid]

Look at pdf page 38 here: https://www.electro-tech-online.com/custompdfs/2012/02/chapter04_image20sensors.pdf at the linear image sensors. It looks as if you can determine 0.5 mm over about a 5 cm distance

Another way to look at this problem would be say a slide with an image sensor on it. The slide could move at a slow rate within limits until the image sensor is found.

Once it is found it would then go into a micropositioning mode or it could just read out it's position e.g The beam is x pixels from the top or convert that to a distance. If you were able to micro position the sensor, then you could have it always lock to a given value.

Or maybe some sort of manual adjustment that you do through an RF link.

See, I'm not sure which end you want to be the variable. Are you shooting for a target at the stick end and positioning the level or are you setting the level and trying to find where it is at the stick end?

 

[Duggie]

Thanks Simple. Haven't looked at link yet. Laser is fixed position, rotating horizontally 360deg, generating a virtual flat level plane. You move the detector up and down, When it lights 'on grade' (middle of detector is gettin the laser beam) then measure from the detector to the ground, at numerous locations, to measure the fall / lay of the land. Trying to avoid any mechanical dependence, because this new detector will be mounted on the lift arm of a loader bucket- NOT a smooth ride, don't want to have to protect a moving parts design from its rough lifestyle..
Thanks for the help, I'll look at pdf.

 

[KeepItSimpleStupid]

At least I see what you want to do. Basically use the level in a backwards fashion. I've seen the levels at work in a landscaping application.

And I had someone do some surveying for me with a transit for a drainage slope.

 

[KeepItSimpleStupid]

I'll throw this at you too: **broken link removed**

A linear motor with virtually unlimited length.

 

[Duggie]

Just looked at your 1st pdf. JUST AMAZING. Thats the **** I'm chasing. Just brilliant, THANKS. Now I still need someone to design me a circuit..(Using detector array..)??
Um, I'm 2 dumb to understand what 2nd pdf is sorry.. U threw it at me, and I missed it...

 

[KeepItSimpleStupid]

The second PDF is about a Linear Motor. See: https://en.wikipedia.org/wiki/Linear_motor

Think Magelev trains. Look back apage: **broken link removed**

 

[Duggie]

Ur help has been excellent, thanks. How do u control those motors you have exampled please? Straight voltage? Can you recommend a site to design me a detector circuit using the detector arrays you pdf'd please?

 

[KeepItSimpleStupid]

Let me think for a while. I just happen to be awake at 5:00 AM in the morning today.

I had another off the wall thought. Suppose you were to take a small metallic parabola with a detector of some sort at the focal point. So, if you could find the beam within that space (think small satellite dish) you would know that the beam is within 1 ft or so. So now you could measure with something more conventional. A solar simulator has one in it.

Silly ideas, I know.

 

[KeepItSimpleStupid]

The bottom line is that they want to sell you a system, so they provide the controller.

PDF page 15 here https://www.electro-tech-online.com/custompdfs/2012/02/AerotechLinear_Motors.pdf now makes some sense as to how they work.

This https://www.electro-tech-online.com/custompdfs/2012/02/00857a.pdf might provide some insight.

With a BLDC motor, there are three coils and there is a sensor that basically feeds back the position of when only one of the coils in energized. So, there would be one of three positions.

To rotate a motor, you energize the coils based on which sensor(s) is active. You can determine the RPM by monitoring just one sensor. If you actually vary the current in each phase you could microposition the motor.

So picture 3 coils that repeat linearly for the length of the linear motor. Again picture 3 sensors that repeat. Now connect every 3rd sensor in parallel and every 3rd coil in parallal. Now as it moves, a new set of coils are used, but each repeating set of 3 has the same magnetic field. Since there is nothing to move except where the actuator is, the actuator moves. I could imagine that crude positioning could be determined by the sensors in the motor alone and past actions.

An encoder is a way of measuring position. It's nothing more than a disk with two optical sensors which generate pulses. You can determine the direction and speed based on this sensor.

I know you said map terrain, but you didn't give any real specs. Resoluton, height etc. Distance to be traveled etc. How accurate the x y and z position should be. etc.

Suppose I wanted to map an area 20' in diameter and 10' is the max depression. So I position my reference in the 10' depression and my rotating level is in the center.

So, let's use polar coordinates from the camera and we roll around this thing that looks like a medical I-V cart, but with some way of leveling it. Maybe you don't want to level it and use the sensor to determine the angle.

So, you set it down. Pull it taught. Push a button. The gismo moves the linear sensor into the field of view of the laser. It knows the height to the precision of the encoder. It could even find the angle (if shallow) using the linear position sensor. Then you move to the next position.

This could probably be totally automated. Move while keeping a certain amount of force on the cord. Find the laser beam. Level itself. Find the height. Move a distance theta and do it again. A position sensor would keep track of theta too.

When your done, convert everything back to Cartesian co-ordinates (x,y).