Like a Bat with HC SR04

How to use HC SR04 to measure distance (with noise filter).

BeginnerProtip1,863

Things used in this project

Hardware components

Ultrasonic Sensor - HC-SR04 (Generic)

Raspberry Pi 2 Model B

you can use this

Raspberry Pi 3 Model B

or this

MinnowBoard MAX

or this

Qualcomm DragonBoard 410c

or this

Software apps and online services

Microsoft Windows 10 IoT Core

PowerBerry SUP - StartUpPackage

PowerBerry POWER-KI - Programming Language

Story

This simple program demonstrates how simple it is to use the HC-SR04 to measure distance with centimeter resolution.

The principle of operation is that of the sonar. Applying a pulse of 10 microseconds to TRIG, HC-SR04 emits an ultrasonic signal. When the reflected wave is received, ECHO signal is raised (0-1-0) for a time proportional to the time taken, outward and return. In our program all is managed by HCSR04 VAR.

POWER-KI WorkBench : HCSR04 VAR

The INIT is called with the pin number for pulse and echo (pin 4 and 5 that you can change). It sets the TRIG Method for the Echo pin and wait, till the and of the program, for computing the distance.

The TRIG does a very simple job: it computes the microsecond between the set (1) and reset (0) of the ECHO edge signal.

       
#if(trg_edge);
    eTime=trg_tmrUs;
#else;
    #while(1);
        #if(~eTime);
            mTime=trg_tmrUs-etime;
            eTime=£;
            #break;
        #end;
        yield;
    #end; 
#end;

Sampling and Filtering

The main loop of the INIT method sends a pulse and waits for a reply (mTime not NULL) or a timeOut. The code has a two stage filtering:

After three valid values the middle is used

The average is computed on the last 5 values

The result value (distance) is shown in the following page.

Get Used to and Learn

The APP is contained in PowerBerry SUP (StartUpPackage) and is in executable source code that you can open/study/change with POWER-Ki WorkBench.

Free Use

POWER-Ki and PowerBerry can be used freely.

Code

=========================================================================
(VAR) HCSR04
--------------------------------------------------
eTime:   (elapsed time)
mTime:   (measured time)
distance:   (distance)
SV: 
NV: 
Lis: 
VT: 
md: 
--------------------------------------------------
========================================
(MTHD) Init
--------------------------------------------------
PinOut:   (Output pin)
PinInp:   (Echo pin)
refDat:   (Reference to the da)
gpio: 
trg: 
tmo: 
ntmo: 
step: 
--------------------------------------------------
..............................
gpio=HIO_GPIOnew;
trg=TRIG(£\HCSR04\TRIG,"trg_pin,trg_val,trg_edge,trg_tmrUs");

HIO_GPIOset(gpio,pinInp,0,trg);
..............................
(WHILE) while
 Loop
--------------------------------------------------
_COND_: 
--------------------------------------------------
..............................
_COND_= runFlg@\Main;
..............................
(DO) do
..............................
#if(~lis==0);lis=lis_new;#end;
ntmo=0;
md=0;

#while(runFlg@\Main);
mTime=£;

HIO_GPIOpulse(gpio,pinOut,1,10);

tmo=tmr+500;
#while(!mTime and runFlg@\Main and tmr<tmo);
sleep(5);
#end;


#if(tmr>=tmo);#skip;ntmo=ntmo+1;#end;

#while(1);

#if(mtime > 38000 or mTime<58*4);#break;#end;

#if(LIS_NUM(lis)<3);
LIS_ADD(lis,mTime);
#break;
#end;

LIS_SORT(lis,£ASC);
mTime=LIS_POS(lis,2);
lis_clr(LIS);

#if(abs(mTime-md) > md*.4);SV=0;NV=0;#end;

#if(NV>=5); SV=SV-md;NV=NV-1;#end;
SV=SV+mTime;
NV=NV+1;
md=SV/NV;

distance=FLT(md/58,0);

#break;
#end;

sleep(20);
#end;
..............................
..............................
HIO_GPIOset(gpio,pinInp,0,£);
trash(gpio);
trash(trg);
..............................
========================================
(MTHD) TRIG
--------------------------------------------------
trg_pin: 
trg_val: 
trg_edge: 
trg_tmrUs: 
--------------------------------------------------
..............................
#if(trg_edge);
eTime=trg_tmrUs;
#else;
#while(1);
#if(~eTime);
mTime=trg_tmrUs-etime;
eTime=£;
#break;
#end;
yield;
#end;
#end;
..............................
========================================