Optical sensors are among the sensors that are often used for distance measurements. An optical distance sensor is basically made of a light emitter (Tx) such as a light emitting diode (LED), a light receiver (Rx) such as a photosensitive transistor, and a circuit supporting the operation of the Tx and Rx. The distance measurement is made using the reflection technique in which the Tx emits a light to a target and the Rx receives the reflected light from the target. When designing such a sensor, the factors that affect the performance of measurements need to be taken into account. Among them are light intensity and wavelength. The purpose of this thesis project is to investigate and evaluate the optical sensors, in application towards distance measurement. To this purpose, three pairs of LEDs and phototransistors are selected which three distance sensors are made of. The lights from three LEDs have the wavelengths of 830, 880, and 940 nm, respectively, which are all in the infrared (IR) spectrum. A circuit was made for each sensor in order to read the measurements and then calculate the distances, and then tested in a testbench. The testbench has a metal plate used as a measurement target which can be moved up and down by a motor. Each of the circuits was placed on the testbench’s base, and a microcontroller (Arduino Uno R3) was used to read the measurement of voltage (proportional to the light intensity) from the Rx as the distance to the target changes up to one meter. The measurement data is then presented on a graphical interface to analyse the relationship of light intensity with distance. Curve fitting and optimization techniques are applied to the data to construct a smooth function that approximately fits the data. An operating range where the distance can be reliably determined is determined for each unit. The circuit design and technique was proven to work for operating ranges up to one meter. A limited moving range of the testbench does not allow for experiments at distances higher than one meter and the microcontroller is ill fit for measuring low voltages, but these can be addressed by improving the measuring environment without changing the underlying technique. The test results of the distance measurement reveal that the three sensors give similar distance estimations between different configurations over an operating range of up to 0.9 meters. Future work should consider improving the circuit design to reduce power ripple and increasing operating range.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-475170 |
| Date | January 2022 |
| Creators | Wigzell, Olof |
| Publisher | Uppsala universitet, Signaler och system |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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