Historically, the job of land surveying has involved taking precise measurements at various locations for the purposes of determining borders, scouting suitable construction sites, and for scientific endeavors. However, in modern times, somewhat expensive equipment is required in order to get the most accurate measurements possible. The use of lasers, robots, and GPS all need specialized equipment, therefore, Fieldman on Hackaday.io decided to create his own solution that is both inexpensive and accurate down to a couple of centimeters over a large area.
Fieldman’s design involves the use of two base stations placed into the ground on top of stakes and an additional station that moves around within a 25 by 25 meter area. Each individual unit contains a single microphone and speaker, along with a wireless transceiver for communicating with other units within a range of around 100-300 meters. To get the location of the mobile station, it starts by telling one unit that it should listen for an audible sound and then reply by sending a sound of its own. This process is repeated for the second base station so that two distances can be calculated and used to determine where the mobile unit is located with some simple math.
Every unit houses the same PCB, which improves the simplicity and helps reduce costs even further. Originally, Fieldman had wanted to use the CC1312R High-Performance Sub-1 GHz Wireless MCU IC from Texas Instruments directly due to its good spec sheet and low price, but the small size made it difficult to solder by hand. Instead, he opted for a slightly larger module that contains the same chip but in a far easier package. His PCB design incorporates this module along with power management circuitry, the microphone and its amplifier, a speaker driver, a temperature sensor, and programming headers. Unlike the mobile station, the two base stations are powered by a pair of rechargeable AAA batteries that last for about 15 hours of continuous use.
As stated previously, the mobile station (referred to as “M”) is responsible for starting the measurement. It sends a signal over a radio link to one of the two base stations, which puts the station into listening mode. Once the sound has been picked up and matched with the reference tone sweep for extra accuracy, it records the time between the first radio message and when the sound arrived. This process is repeated in reverse to get the distance for the other direction, and the two distances are averaged and combined with the air temperature to get a distance value. After the mobile station has measurements for the distances between the two base stations and its own distance to them, the Pythagorean theorem can be used to calculate a location on the 2D plane down to the centimeter.
Due to the low-cost nature of this land surveying solution, there are countless ways to use the system and innovate it further for improved specifications. Additionally, Fieldman’s software could be expanded to include new functionality or diagnostic data when the need arises. To see more information about this project, you can visit its write-up here on Hackaday.io or watch his excellent explanation video here on YouTube.