"Energy Saving Star" EFM32 Application Solution - Handheld Laser Distance Meter

Overview

With the development of modern technology and the improvement of people's living standards, portable laser rangefinders are widely used in various industries, such as construction, golf, driving speed and distance measurement. Laser is an electromagnetic wave with strong directionality, good monochromaticity, good coherence, and high brightness, making it the preferred electromagnetic wave for distance measurement.

The commonly used laser ranging methods are:

1. Pulse ranging method: Use a pulse laser to emit a single laser pulse or a laser pulse train, measure the round-trip time for the laser pulse to reach the target and return from the target to the receiver, and calculate the target distance. This method has a large error and is suitable for long-distance measurement.

2. Interference distance measurement: Using the principle of light interference, the distance is measured by measuring the interference fringes between laser emission and reception. This method has very high accuracy, but it can only measure relative distance, not absolute distance.

3. Phase distance measurement method: Use a continuously modulated laser beam to illuminate the measured target, and calculate the distance of the target by measuring the phase change generated by the beam during the round trip. This method can achieve high-precision long-distance measurement when using cooperative target reflectors and multiple rulers.

System Structure

EFM32 is a high-performance, low-power 32-bit microcontroller designed by Energymicro of Norway using the ARM Cortex-M3 core. It has outstanding low-power characteristics and is suitable for "three meters" (electricity meter, water/heat meter, gas meter), industrial control, alarm security system, health and sports application system, handheld medical equipment and smart home control.

FIG1 is a block diagram of the structure of a handheld laser rangefinder, including power supply and charging, laser transmitting circuit, laser receiving circuit, storage chip, display module, main processor, and control buttons.

Figure 1 Block diagram of handheld laser rangefinder

Power supply and charging

The handheld laser rangefinder is battery powered and has a charging circuit. The operating voltage of EFM32 is 1.8~3.8V, and the operating voltage range is relatively wide. [page]

Laser emission circuit

The modulated signals of different frequencies are generated by PWM to achieve multi-measurement. The modulated sinusoidal signal is transmitted to the target through the laser transmitter.

Laser receiving circuit

The received signal is amplified by a high-speed operational amplifier and sampled by an ADC to determine the waveform phase.

Memory IC

Save the measurement results.

Display Module

The measurement results can be displayed on LCD or TFT, and previous measurement results can be searched or other functions can be displayed.

Main Controller

Different models of EFM32 can be selected as the main control MCU according to the different functions of the rangefinder. EFM32 has good compatibility, and the pins of the same numbered chips are pin-pin compatible. In low-end applications, the EFM32TG series can be selected as the main control, and its flash and RAM resources are 8~32KB and 2~4KB; in high-end products, the EFM32LG series can be selected, which is pin-pin compatible with the EFM32TG series, with flash and RAM resources of 32~128KB and 8~16KB, and with TFT driver and USB.

Control buttons

Define different functions according to the product usage area.

Solution Advantages

Compared with the traditional 8-bit and 16-bit single-chip implemented handheld laser rangefinder, this solution based on EFM32 has the following advantages:

Ultra-low power consumption

EFM32 is the world's lowest power 32-bit microcontroller. In EM2 mode with RTC and DMA running, the power consumption current is only 900nA, and it can be as low as 600nA when RTC is not running, and it is only 20nA when RAM data is not saved. Since the handheld laser rangefinder is powered by a battery, it has certain requirements on power consumption, so the low power consumption of EFM32 has obvious advantages.

High integration and high performance

EFM32 is a Cortex-M3 core, and the core's instruction efficiency and code density are higher than those of traditional 8-bit microcontrollers, especially in algorithm processing, which has a significant advantage in calculating phase difference. The chip has a 12-bit ADC with a sampling rate of 1M, which can achieve precise timing sampling and data storage with PRS and DMA, and obtain the phase of the returned waveform more accurately, so that the MCU has the ability to process and respond to external events faster, which is more suitable for this application. In addition, EFM32 integrates up to 8X36 LCD drivers on the chip, and even supports TFT screen drivers with 16-bit RGB interfaces. The rich integrated peripherals provide a variety of choices for different system applications.

Good scalability

EFM32's TG, G, and GG series have good compatibility, and chips of the same model but different series are pin-pin compatible, ensuring that users can tailor different functional requirements on a unified hardware platform. Flash resources range from the lowest 4KB to 1024KB, and RAM resources range from 2KB to 128KB.

Summarize

EFM32 has excellent low power consumption characteristics and is very suitable for handheld laser rangefinder applications that have certain requirements for low power consumption. The EFM32 core adopts the currently popular Cortex-M3 design, which greatly shortens the development time of developers. EFM32 has rich peripherals, which provides conditions for system expansion functions and cost reduction.