Rotary Laser Level Receiver Circuit ... #2

Thread Starter

arnolde

Joined Oct 21, 2020
9
I want to build my own laser-guided grader (using Arduino to control the hydraulics) and the cheapest comparable receivers (with more than 10cm detector area) are around 1000€, and I need 2 of them, so I want to build my own also. I am very interested to hear if anyone (maybe the thread poster?) actually succeeded in building this. I would make a printed PCB and maybe even a batch of 100 or so to share the costs, I'd expect the kit cost to be <100$ each. If anyone is interested please contact me at < mod: deleted email> (but please write a meaningful Subject line as I get lots of spam!)

Mod: Link to old thread
https://forum.allaboutcircuits.com/threads/rotary-laser-level-receiver-circuit.155616/post-1343047
 
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jpanhalt

Joined Jan 18, 2008
10,515
Re: Detector length

Can you use light guides (fiber optic) to go from a longer area to a much smaller detector? Diode arrays for spectrometry and imaging have been around for a long time. Just one example, the MLX75306 is about $14 and has 142 elements in a 7-mm high array. That was just the first hit.

I suspect the detector is the key part and the most challenging part will be dealing with stray light.
 

Thread Starter

arnolde

Joined Oct 21, 2020
9
Right now I plan to use a long string of photodiodes i.e. BP104 like in the photo in the first post in the previous thread, and use those to a) trigger an interrupt on the microcontroller and b) use a latching shift register like 74HC597 to latch and read which photodiode fired. I'm not sure though if the 1µs laser pulse will be strong enough over the ambient daylight to be detected easily. Using a red light filter should help but will it be enough?
 

jpanhalt

Joined Jan 18, 2008
10,515
Passive filters probably help, but the IR modules with which I am familiar modulate the light beam (something like 30 kHz to <100 kHz) so that only light with the correct modulation frequency registers a response. Here's one example of a large number of such detectors: https://www.vishay.com/docs/82881/tsop131df1p.pdf Details are on page 3 of that datasheet. A steady source of light does not register.

I have used those detectors in bright daylight without interference. Of course, range may be a problem, and there is a definite period needed for detection.
 

Thread Starter

arnolde

Joined Oct 21, 2020
9
The rotating laser transmitter will generate a pulse of a few µs (depending on distance) at 8-10Hz. How can we easily filter that (for 64 seperate sensors)? (Note: The frequency is probably pretty stable, either at 8Hz or at 10Hz. The 1µs is at 100m distance, at only 10m distance it will be longer)
 

Thread Starter

arnolde

Joined Oct 21, 2020
9
BTW: This is the rotation laser I want to detect (I actually have exactly this one): https://www.aliexpress.com/item/4001022181272.html
It uses a 635nm laser diode and rotates at 600rpm, so 10 Hz was correct (can also be reduced to 5Hz or 1.5Hz to increase the range)
It includes a receiver similar to the one the first thread's starter has (smaller though). This is what I want to copy, and build one about 30cm long, to control my hydraulics with.
I just saw it includes "laser goggles" and remembered I have a pair too, which I never used - I will dig them out and try them today :) maybe I can fabricate a filter from the (plastic) glasses.
 

Thread Starter

arnolde

Joined Oct 21, 2020
9

jpanhalt

Joined Jan 18, 2008
10,515
An inexpensive filter will probably not be a bandpass, but rather something like this (Source: Edmund optics):

1603292907957.png

Of course the Sun emits strongly in the deep red and infrared parts of the spectrum. I suspect your detector would look for a "blip" in intensity against some arbitrary and variable background intensity. You could set minimum and maximum widths to filter noise. If the rotation is 10 Hz, you might be able to use a missing pulse detector to determine when the beam is on or off target. That would have to be able to discriminate between each of the photodetectors, which may be why some devices only report on target, high, or low (e.g., all outputs off target are treated as one) .
 

Thread Starter

arnolde

Joined Oct 21, 2020
9
I just took apart my own laser receiver and was surprised not to find a row of photodiodes as I hoped, but rather 2 small photovoltaic cells (each about 5x20mm), one below and one above the centerline. Okay, that sure simplifies things, the receiver circuit only needs to "watch" for pulses at the expected frequency (or one of the expected frequencies) on 1 of the 2 cells, instead of dozens of small sensors. Now I need to think about that concept, and if I might want to copy that. But the commercial grader by Bobcat that I recently used had the option to adjust the grade up and down by a few centimeters at the touch of a button, that option would not work with this solution. But maybe it's not that important. Hmmm.


laser-receiver-photocells.jpg
 

Thread Starter

arnolde

Joined Oct 21, 2020
9
@ericgibbs What are you trying to tell me? That 1 chip contains multiple OPAs? Yes, but using quad OPAs still means 1/2 chip per sensor, plus (in the linked circuit) 4R and 3C. Means 32 chips and 448 passive components for 64 channels... (in addition to the 8 buffering shift register chips) I was hoping to get by with fewer components ;-)
 

Dodgydave

Joined Jun 22, 2012
9,666
I just took apart my own laser receiver and was surprised not to find a row of photodiodes as I hoped, but rather 2 small photovoltaic cells (each about 5x20mm), one below and one above the centerline. Okay, that sure simplifies things, the receiver circuit only needs to "watch" for pulses at the expected frequency (or one of the expected frequencies) on 1 of the 2 cells, instead of dozens of small sensors. Now I need to think about that concept, and if I might want to copy that. But the commercial grader by Bobcat that I recently used had the option to adjust the grade up and down by a few centimeters at the touch of a button, that option would not work with this solution. But maybe it's not that important. Hmmm.


View attachment 220211
Looks a 28pin Pic from Microchip..so must be some software development ..
 

RobHalleNL

Joined Oct 25, 2020
4
Hello Arnold,

I am looking for a similar solution, I am making a grading board, something like this:

Kilverbord.jpg

and want to be able to control the hydraulic valve by hand, with a switch, as well as with a laser receiver.
My rotation laser is the same as you have.

Rotatielaser.jpg

I think the biggest challenge is to use a sensor that does receive the laser signal in daylight.

Hopefully we will come to a workable solution.
 
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RobHalleNL

Joined Oct 25, 2020
4
Unfortunately, the original receiver has an LCD display.
If it had three LEDs, you could easily branch out the status of the LEDs.

I tried to measure signals on the PCB hoping to find the three status signals.
Unfortunately, not found.
 
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