Tachometer vs LIDAR ?  - Page 1
Forum section: electronics / projects

author: rajhlinux
author_rank: Contributor
timestamp: January 02, 2021, 11:31:08 am
content: Hello, Happy New Year to all.I would like to measure the RPM of a spinning disc using the theory of a "laser tachometer".Was wondering maybe I could do this using a "LIDAR" module, such as this:https://www.ebay.com/itm/50m-164ft-Laser-Distance-Measuring-Sensor-Module-UART-output-for-arduino/254161557105?hash=item3b2d359671:g:UIsAAOSwdfVciERCYou think I'll be able to read accurate readings in the range of 20,000 RPM using the above LIDAR module?I couldn't find such information on the internet, also couldn't find the modulation frequency of these LIDAR modules.Thanks.

author: mikerj
author_rank: Super Contributor
timestamp: January 02, 2021, 01:35:22 pm
content: The answer is no. The purpose of LIDAR is to measuring distance, not the frequency of a rotating target.You can buy a hand held laser tachometer for somewhat less than the price of that LIDAR module (e.g. UNI-T UT373 which will measure up to 99999 RPM)

author: rajhlinux
author_rank: Contributor
timestamp: January 02, 2021, 02:14:47 pm
content: Thanks for your quick reply.I was hoping I could get two functionality from that LIDAR module:1) Laser Tachometer2) LIDARAll in all, glad I didn't buy that LIDAR module.So this "Laser Receiver - Transmitter" module should do the trick for reading the rotating target?:https://www.amazon.com/gp/product/B00NJNYQ9G/ref=ask_ql_qh_dp_hzaThere also a handheld device "Dt-2234c+ digital tachometer 99,999RPM" for $16 many reviews showed it is reliable:https://www.amazon.com/gp/product/B07G5VLQ7D/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1Not sure how I'm going to get the readings into a microprocessor such as Arduino, gunna have to open it up and do some reverse engineering...But the first link can be easily accessed by an Arduino.

author: mjkuwp
author_rank: Unknown
timestamp: January 02, 2021, 03:09:58 pm
content: I recommend this one: Dt-2234cit will have the exact circuit for acquiring the high speed pulses. the other device may not be optimized for that.The theory of operation is photoconductance. A diode emits light when current passes forward. Likewise, when light falls on the diode a small current will be caused in the reverse direction. The tachometer will have some levels of filtering to acquire this signal and square it up.I guess it will be easy for you to find a connection for the microcontroller.

author: rajhlinux
author_rank: Contributor
timestamp: January 02, 2021, 05:36:21 pm
content: Thanks for the reply.I already purchased a "Dt-2234c+" and you have the "Dt-2234c" (without the "+"), hope it's not much of a difference.It should come after few days from Amazon.I'll take a look at it and also take some High Resolution pictures of the PCB, hopefully you Pros can help me hook it up with a microcontroller.Need a decent accurate tachometer because I'm building a balancing device which uses a sensitive accelerometer to detect vibrations, so that I can balance motor shafts/stators, propellers, spinning wheels...Here is an example of the balancing device project:Overall, I'm designing a polygon laser scanner which uses a transparent glass prism rather than a mirror for scanning the laser.Since I'm using a custom made glass prism, it needs to be balanced with the polygon motor (I removed the original mirror) at high speeds around 10K-20K RPM.This polygon laser is going to help me design homemade PCB with a promising resolution of 0.02mm traces/spaces (Good for chips with PBGA).Here is the project which I am following for the polygon laser:https://hackaday.io/project/21933-open-hardware-fast-high-resolution-laserThanks.