Welcome to the training module on the Handheld Laser Rangefinder .
This training module will introduce the handheld laser range finder and recommend a solutions for its use.
Soon after the invention of the laser, it has found a place as a useful tool in many scientific, military, medical and industrial applications. Here we will look at an instrument using laser technology, Laser Rangefinder. As its name suggests, a handheld laser rangefinder is an instrument intended for distance measurements, usually in the open air. The range finder determines distance to a targeted object by sending out a laser emission and measuring the reflected emission returned to the detector housed in the rangefinder unit. When taking a measurement, a laser rangefinder emits hundreds of laser beams in an approximate half-second period to boost measurement accuracy. This also improves accuracy, as a single laser beam can miss a target that is too small.
There are two ways to measure the distance. One is by applying the time of flight (TOF) principle, called pulse. Another is based on phase-shift measurement. The TOF laser rangefinder transmits a laser signal toward a target, and then the laser signal is reflected back to the laser range finder, whereby the laser finder measures the traveling time of the laser signal. Accordingly, the distance of the target is derived from the light speed multiplied by half of the fly time. However, the phase-shift based laser rangefinder emits the laser beam which is modulated continuously to the target and then detects the variance of the phase during the traveling time. By calculating the variance of the phase during the traveling time, the phase-type laser rangefinder can get the distance easily. The TOF method is the most widely used technique for long distance measurement over length scales of several hundred meters to tens of kilometers. The phase shift technique is usually used to measure the short to intermediate distances up to several hundred meters.
Laser rangefinders are very fast at measuring distance. They have real-time processing capabilities. Such devices also measure the true, straight line distance between two points, without the bend or sag that commonly occurs with a tape measure. So it can obtain more accurate measurement. It is much easier to read the digital display on a laser rangefinder device, which can be held in a convenient position, than to read a tape measure that needs to be held in the measuring position. The rangefinders can measure the distance in places that are difficult to reach, like high ceilings, tall buildings or even water. Some rangefinders are capable of sending the measurements directly to a computer for further processing. Laser rangefinders allow you to measure areas that are not normally safe to access.
Laser rangefinders are generally used for longer distances and when accuracy is not as critical. There are several different potential uses for laser rangefinders. In the military, they can be used for military reconciliation and engineering. Laser rangefinders are used extensively in 3-D object recognition, 3-D object modeling, and a wide variety of computer vision-related fields. Laser rangefinders may be effectively used in various sports that require precision distance measurement, such as golf, hunting, and archery. Laser rangefinders are also used in several industries like construction, renovation and real estate as an alternative to a tape measure.
Performance characteristics of various laser rangefinders are affected by things such as the size and reflectivity of the targeted objects as well as weather conditions. Depending on the requirements of the applications, several terms are necessary to consider during the selection of a laser rangefinder. Therefore, when designing a laser rangefinder, designers must know them clearly in order to select suitable components for the design. The major features of these devices are reflectivity, effective range, view indicators, battery sizes and body construction. Reflectivity refers to the amount of laser emission signal that a target will reflect back to the emission source. Highly reflective targets can be ranged at greater distances than other similarly sized targets. The strength of the laser emission and sensitivity of the rangefinder's detector will determine maximum range to target determination.
The electronic system of a handheld laser rangefinder is composed of laser transceiver circuit, frequency synthesis and phase-detection circuit, MCU and LCD display. The transceiver circuit implements amplitude modulation on laser by using a high frequency sine-wave signal before the laser is transmitted. When the laser is reflected back by an object, the transceiver circuit converts it into electronic signal by its electro-optical component (normally it’s a PIN or APD). The electronic signal will then be amplified by a low noise amplifier and sent to the mixer, which down-converts the high-frequency modulated signal into intermediate-frequency signal for the purpose of increase phase-detection resolution. The phase-detection circuit implements waveform shaping over the intermediate-frequency signal and a local reference signal to produce a square waveform. These square waves are sent to comparator circuit to find out phase shift, which will have “AND” operation with the counter clock signal to produce a result used by the MCU. Finally the MCU will calculate the distance based on this phase shift and displays the result on the LCD.
In order to calculate the range, laser light must be transmitted using a laser and laser driver. Our solution uses a laser diode as the light source to produce the laser. It should have a low transmission power in handheld applications, normally lower than 5mW. The laser will need to be pulsed and depending on what driver is used the laser may need to be pulsed at up to tens of megahertz. The main performance characteristic that needs to be considered was how fast the laser diode could be pulsed. We show some Laser Diodes with the most commonly requested specifications in the table
The laser light is received by a photodiode and then amplified for further processing. If the photodiode cannot detect the reflected light then no matter how good the rest of the signal processing is, the receiver will be useless. Two photodiodes are used in our solution. One is used to convert the modulated laser reflected from an internal mirror into electronic signal; another for converting the modulated laser reflected from object into electronic signal. The output of the photodiode is initially amplified so that the signal can be processed more easily
In the transmitting and receiving paths, the mixer is responsible for mixing the high-frequency signal of transceiving path and local oscillation signal to provide intermediate-frequency signal output. In the reference path, the mixer is used to mix the high-frequency signal of reference path and local oscillation signal to provide the intermediate-frequency reference signal output. We select a series of mixers with wide input frequency range and low intermodulation distortion.
The AD8343 is a high-performance broadband active mixer. With wide bandwidth on all ports and very low intermodulation distortion, the AD8343 is well suited for demanding transmit applications or receive channel applications. The AD8343 provides a typical conversion gain of 7 dB. The integrated LO driver supports a 50 Ω differential input impedance with low LO drive level, helping to minimize external component count.
The microcontroller is required to record the range of the object being detected and then transmit the data for display. When a calculation is in progress and a pulse is received, the microcontroller must record the value of the counter and store it in the memory. When a pulse is received the microcontroller must also sample the output of the phase shift detection circuit in order to get the range of the object. To sample the output, the microcontroller must have an analogue to digital converter (ADC). The ADC should have the appropriate resolution so as to meet the accuracy specification of one centimeter. The more samples taken will lead to more accurate the results. So the faster the microcontroller can transmit the data the more accurate the results can be. Once the microcontroller has obtained the values of the range it must transmit them to a display.
The table lists out some additional components which are used in the solution. The power management part can be a DC/DC converter or LDO regulator that provides a wide range of input voltage, stable output voltage, and low standby current. As it is a handheld device, a battery is used as power source which may be a a rechargeable battery with small size, low weight, large capacity and long service life. The battery management parts help to extend battery life. The external memory devices are used to store range data and program.
Thank you for taking the time to view this presentation on the Laser Range Finder. If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more design resources you may either visit the element14 site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.
1. Handheld Laser Rangefinder
2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>To introduce handheld laser range finder knowledge and recommend a solution for it. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>What is laser rangefinder? </li></ul></ul><ul><ul><li>Applications of laser rangefinder </li></ul></ul><ul><ul><li>Requirements for laser rangefinder </li></ul></ul><ul><ul><li>Block diagram of the solution </li></ul></ul><ul><ul><li>Recommended parts </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>15 pages </li></ul></ul>
3. What is Laser Rangefinder? <ul><li>A laser rangefinder is an instrument which uses laser energy for determining the distance from the device to a place or object. </li></ul><ul><li>When taking a measurement, a laser rangefinder emits hundreds of laser beams in an approximate half-second period to boost measurement accuracy. </li></ul>Source from http://www.nikon.com
4. Different Methods <ul><li>Laser rangefinders can be divided into 2 categories in terms of their operation principle. </li></ul><ul><ul><li>Time-of-flight (TOF) method: a pulse wave is used as the laser beam, also called pulsed TOF laser rangefinder. </li></ul></ul><ul><ul><ul><li>Suitable for long distance measurement: from several meters to tens of kilometers </li></ul></ul></ul><ul><ul><li>Phase-shift method: the phase difference between the transmitted signal and the reflected signal represents a distance. </li></ul></ul><ul><ul><ul><li>Suitable for short to intermediate distance: up to several hundred meters. </li></ul></ul></ul>C is the speed of light in the atmosphere T is the amount of time for the round-trip between source and target ω is the angular frequency of optical modulation Transmitted Pulse Reflected Pulse Phase-shift Rangefinder Target Δ t Transmitted Pulse Reflected Pulse Target TOF Rangefinder T= 0 T= t
5. Why Use it? <ul><li>Time saving </li></ul><ul><li>Accuracy </li></ul><ul><li>Prevention of Errors </li></ul><ul><li>Easy to use </li></ul><ul><li>Ability to obtain difficult measurements </li></ul><ul><li>Data interface </li></ul><ul><li>Safety </li></ul>
6. Target Applications <ul><li>Military </li></ul><ul><ul><li>Provide an exact distance to targets located beyond the distance of point-blank shooting to snipers and artillery </li></ul></ul><ul><ul><li>Military reconciliation and engineering </li></ul></ul><ul><li>3D modeling </li></ul><ul><ul><li>3D object recognition, 3D object modeling </li></ul></ul><ul><li>Sports </li></ul><ul><ul><li>Golf </li></ul></ul><ul><ul><li>Hunting </li></ul></ul><ul><ul><li>Archery </li></ul></ul><ul><li>Industry production processes </li></ul><ul><li>Laser measuring tools </li></ul><ul><ul><li>Alternative to a tape measure </li></ul></ul>
7. Key Considerations for Laser Rangefinder <ul><li>Accuracy: is a measurement of the difference that can be expected between a laser rangefinder's reading and the actual distance measured. </li></ul><ul><li>Laser Power: the optical power level emitted by the laser in a sensor. </li></ul><ul><li>Maximum Range: the maximum distance to which a laser rangefinder can pick up reflected light and obtain an accurate distance measurement. </li></ul><ul><li>Response Time: the delay between the time of a change in the target position and the time a laser rangefinder's output changes. </li></ul><ul><li>Resolution: smallest change in distance that a Laser rangefinder can detect </li></ul><ul><li>Battery life: the time the battery can power the device for normal operation. </li></ul>
11. Broadband Mixer Selection Manufacturer Part Number Description Convert Type RF Frequency (MHz) LO Frequency (MHz) IF Frequency (MHz) Linear Technology LT5526EUF High Linearity, Low Power Downconverting Mixer Downconverting Mixer 0.1-2000 0.1-2500 0.1-1000 Linear Technology LT5512EUF High Signal Level Active Mixer Downconverting Mixer 0.001-3000 0.001-3000 0.001-2000 ADI AD8343ARUZ High IP3 Active Mixer Up/Down-converting Mixer DC-2500 DC-2500 DC-2500 ADI AD8342ACPZ Active Receive Mixer Up/Down-converting Mixer DC-2400 DC-2400 DC-2400
12. ADI’s AD8343 Mixer <ul><li>High-performance active mixer </li></ul><ul><li>Broadband operation to 2.5 GHz </li></ul><ul><li>Conversion gain: 7 dB </li></ul><ul><li>Input IP3: 16.5 dBm </li></ul><ul><li>LO drive: –10 dBm </li></ul><ul><li>Noise figure: 14 dB </li></ul><ul><li>Input P1dB: 2.8 dBm </li></ul><ul><li>Differential LO, IF and RF Ports </li></ul><ul><li>50 Ω LO input impedance </li></ul><ul><li>Single-supply operation: 5 V @ 50 mA typical </li></ul><ul><li>Power-down mode @ 20 μA typical </li></ul>
15. Additional Resource <ul><li>For ordering solution related products, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For more design resources go to </li></ul><ul><ul><li>http://www.element-14.com/community/docs/DOC-22607 </li></ul></ul><ul><li>Visit Element 14 to post your question </li></ul><ul><ul><li> www.element-14.com </li></ul></ul><ul><li>For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility </li></ul>Newark Farnell