Laser Measure Sensor (how to)

[Dashunter]

Hi everyone,

I am new to this forum, and I am looking for guidance in building a laser measuring device. I am trying to find a sensor with a minimum measuring distance below 3 inches and any max above 24 in. Also, I need the sensor to have an accuracy of +/- 1/16 or less. Any suggestions or advice would be helpful. And if someone could give me an idea of all the parts that I might need would be great!

 

[BradtheRad]

The speed of light is so fast that components have a miniscule time to measure a reflected flash , especially at a range of a few inches.
Or perhaps you're thinking of a geometric (triangulation) rangefinder?

Did you see an article describing details of a laser rangefinder?

Did you rule out audio sensor methods? It's much easier to work with that length of timeframe.

 

[Dashunter]

I am comparing this to the Bosch Blaze Pro 165' Laser Distance Measure GLM165-40. Basically, I am trying to build a device that can measure length of something that is placed within two walls. One wall is stationary and the other slides back and forth. It can be thought as the foot measuring device when you go get new shoes but with lasers.

 

[betwixt]

What is the 'moving wall' made of?
Time of flight measurement over such short distances is almost impossible but if you can reflect a spot of light back at a slight angle so you change distance away into a lateral displacement it is very easy. You could also try the interference method, splitting the source light to two paths and mixing the split original with a reflection to see their phase difference.


Brian.

 

[FvM]

Laser interferometer gives high resolution but no absolute distance information. For the intended measurement range and resolution, a laser rangefinder using TOF or multi frequency phase shift methode would be appropriate. There are small OEM modules on the market that can be integrated in your instrument. Building it from the scratch involves advanced skills in high speed electronics and probably 0.5 to 1 man-year development effort.

 

[G4BCH]

Try looking at how tank level measuring radars work. Most use fmcw, but in the dim and distant past I did investagate a potential tank radar product using an ultra wide band pulse. I can't remember much of the details now, but the way of recovering the pulses was by sub sampling. There were two cryatal oscillators used that had a small frequency difference etween them one used for generatiing the TX pulse ( a UWB signal) and the other the sampling pulse. The idea was that the sampling pulse slowly drifted through the TX pulses, it worked very much like a sampling 'scope giving the impression of stretching time.

 

[Dashunter]

What is the 'moving wall' made of?
Time of flight measurement over such short distances is almost impossible but if you can reflect a spot of light back at a slight angle so you change distance away into a lateral displacement it is very easy. You could also try the interference method, splitting the source light to two paths and mixing the split original with a reflection to see their phase difference.


Brian.

The wall will be made of plastic. How does Bosch Blaze Pro 165' Laser Distance Measure GLM165-40 work?

 

[Dashunter]

Laser interferometer gives high resolution but no absolute distance information. For the intended measurement range and resolution, a laser rangefinder using TOF or multi frequency phase shift methode would be appropriate. There are small OEM modules on the market that can be integrated in your instrument. Building it from the scratch involves advanced skills in high speed electronics and probably 0.5 to 1 man-year development effort.

If I used an Ultra-low Power Integrated Ultrasonic Time-of-Flight Range Sensor would that work? Then connected it to a Rasberry Pi to control it?

--- Updated Feb 20, 2021 ---

Update: This seems to be what I am looking for.
TOF10120 Laser Range Sensor Module 10-180cm Distance Sensor RS232 Interface UART I2C IIC Output 3-5V
If I am looking at this correctly this should work, but I do not know if it has the accuracy that I am looking for.

 

[FvM]

According to internet reports, TOF10120 measurements have at least several mm variance. Presume it doesn't fulfill your requirements. The 3" minimum distance will be an issue with laser range finders that have larger dead zone.

Ultrasonic can work, but sound velocity temperature dependency must be considered, also sensitivity to air flow.