Seeed grove ultrasonic ranger

Table of Contents

  1. Hardware
  2. Software

This sensor measures the distance to the nearest object by measuring the time an ultrasound pulse takes to reflect from the object.

Seeed ultrasound range finder

http://www.seeedstudio.com/wiki/Grove_-_Ultrasonic_Ranger is Seeed's docs for the module.

Hardware

The range finder has a 4 pin connector, 3 of which are used. It has GND, Vcc and Signal lines. These are labelled on the board. The docs say the sensor is designed for 5V, but it works fine with the mbed's 3.3V. The signal line can be connected to any of the mbed's digital in/out pins.

To trigger a measurement a short pulse (around 10 us) is sent on the signal line. The ranger then send out some pulses and time when they return. The distance is then returned as a pulse of varying length such that

distance [m] = pulse width [us] / 5800 [us / m]

The two images below show the pulses being sent and received for a couple of different distances.

x pulse x pulse

Software

I've written some code that runs the ultrasound ranger. It uses a /handbook/DigitalInOut to send a pulse and then to measure the width of the returning pulse using a /handbook/Timer. The code allows you to set a cut off time so that, should you lose connection to your range finder, it will return a negative distance and not hang up your program. I've tried this out and it is quite happy for me to disconnect the sensor and it will just return a distance of -1.0 m each loop until I reconnect it and it will resume giving me measured distances.

My code uses a library I wrote to read and write digital pulses:

Import libraryPulse

Output digital pulses of specified length and read the length of input pulses.

and also a library for range finders:

Import libraryRangeFinder

Class to handle triggering and reading the distance measured by a range finder.

This means that you can use a range finder with a very simple piece of code such as:

Import program

00001 /* Copyright (c) 2012 Nick Ryder, University of Oxford
00002  * nick.ryder@physics.ox.ac.uk
00003  *
00004  *  MIT License
00005  *
00006  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
00007  * and associated documentation files (the "Software"), to deal in the Software without restriction, 
00008  * including without limitation the rights to use, copy, modify, merge, publish, distribute, 
00009  * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
00010  * furnished to do so, subject to the following conditions:
00011  *
00012  * The above copyright notice and this permission notice shall be included in all copies or 
00013  * substantial portions of the Software.
00014  *
00015  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING 
00016  * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
00017  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
00018  * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
00019  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
00020  */
00021 
00022 #include "mbed.h"
00023 
00024 #include "RangeFinder.h"
00025 
00026 // Seeed ultrasound range finder
00027 RangeFinder rf(p21, 10, 5800.0, 100000);
00028 DigitalOut led(LED1);
00029 
00030 int main()  {
00031     led = 1;
00032     float d;
00033     while (1)   {
00034         d = rf.read_m();
00035         if (d == -1.0)  {
00036             printf("Timeout Error.\n");   
00037         } else if (d > 5.0) {  
00038             // Seeed's sensor has a maximum range of 4m, it returns
00039             // something like 7m if the ultrasound pulse isn't reflected. 
00040             printf("No object within detection range.\n");
00041         } else  {
00042             printf("Distance = %f m.\n", d);
00043         }
00044         wait(0.5);
00045         led = !led;
00046     }
00047 }     

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