Help Identifying the Sensor in a Laser Detector - Page 1
Forum section: electronics / projects

author: canadaboy25
author_rank: Regular Contributor
timestamp: May 22, 2020, 04:23:54 pm
content: Hey everyone, I'm looking for some help identifying the sensors used in some standard laser detector units.I have two units here which detect the spinning red laser from a rotary laser. I am looking to buy some of the sensors used in these detectors for use in my own project. However, I can't seem to find anything similar to the sensors on the internet.If you zoom into the sensor on the NWi unit, you can see that the sensor panel is made up of two elements split in the middle. The operation of this unit is very simple. When the laser is hitting the lower half of the sensor, the display shows an up arrow and vice versa for the top half. When the laser is right in the middle and hitting both halves, the unit displays level. The thin silver piece running vertically must be some sort of photo diode as it produces a voltage of about 20mV when a light is shined directly on it. I have searched through pretty much all of Mouser's and and Digikey's photo diodes and found nothing similar. All of the photo diodes I have found are in small round packages which is not convenient for detecting a spinning laser as they are very small and seem to be very dependent on the angle that the light hits them. The sensors on the laser detector units are able to detect the laser even at angles over 45 degrees.The Topcon unit is a little more complicated as the up and down arrows on the display grow larger and smaller as you raise the unit up and down. If you zoom in onto that sensor you can see that each half of the sensor has 4 small wires in it which are spaced evenly at the middle and meet at the ends. This obviously creates some type of variable output depending on where the laser is. I have not tested the output from this sensor but I imagine it works in a similar way to the other one.I am not looking for something as fancy as the variable sensor in the Topcon unit. If anyone has some idea as to what the linear photo diode type elements in the NWi unit are, that would be very helpful.Thanks

author: Marco
author_rank: Super Contributor
timestamp: May 22, 2020, 05:08:34 pm
content: Are you quite sure they aren't just linear image sensors with more connections underneath?

author: canadaboy25
author_rank: Regular Contributor
timestamp: May 22, 2020, 05:13:54 pm
content: Quote from: Marco on May 22, 2020, 05:08:34 pmFor the Topcon unit with the variable sensor, I am not certain how it is set up as I have not looked very closely at it.However, the NWi unit with the simple two part sensor is definitely just a two connection element that generates voltage when light hits it. Each half has only two connections. I can hook a scope up to the sensor and see the voltage pulses from the sensor when the laser hits it without even having a battery in the unit. This is the sensor I am interested in.

author: Marco
author_rank: Super Contributor
timestamp: May 22, 2020, 05:38:31 pm
content: I guess the triangle shapes wouldn't make much sense for a linear image sensor either.Maybe they make it themselves with PV ink?

author: awallin
author_rank: Frequent Contributor
timestamp: May 22, 2020, 05:50:52 pm
content: position sensitive photodiode?something like these:https://www.hamamatsu.com/eu/en/product/optical-sensors/distance-position-sensor/psd/one-dimensional-psd/index.htmlhttps://www.on-trak.com/1lseries.htmlor maybe from p50 herehttps://sphereoptics.de/wp-content/uploads/2017/08/OSI_Si-Photodiodes.pdf

author: moffy
author_rank: Super Contributor
timestamp: May 24, 2020, 04:04:38 am
content: They are probably quadrant photo diodes e.g.:https://www.first-sensor.com/en/products/optical-sensors/detectors/quadrant-pin-photodiodes-qp/You measure the current out of each of the quadrants and when left=right and top=bottom the beam is centered.