brainwagon

I intended to play around with some of the NRF24L01 radio modules I have around, but my brain didn’t feel up to it after a day of debugging. So, instead i dusted off a Parallax PING))) sensor that I’ve had around for a long time. I thought it might be fun to see if I could use the OLED display to display the distance measured by the sensor. While watching Agents of Shield, I came up with the following tiny bit of code, demo’ed below.

[sourcecode lang=”cpp”]
#include "U8glib.h"

U8GLIB_SSD1306_128X64 u8g(U8G_I2C_OPT_NONE);

// _
// ___ (_)__ ___ _
// / _ \/ / _ \/ _ `/
// / .__/_/_//_/\_, /
// /_/ /___/
//
// A simple rangefinder program using the Parallax PING sensor
// Writes display out to my tiny OLED display…

const int pingPin = 7 ;

char dbuf[10] ;

void
draw()
{
u8g.setDefaultBackgroundColor();
u8g.drawBox(0, 0, 128, 64);
u8g.setDefaultForegroundColor();
u8g.setFont(u8g_font_10x20);
u8g.drawStr(14, 42, dbuf);
u8g.drawStr(94, 42, "cm");
}

void
setup()
{
Serial.begin(9600);
}

void
loop()
{
long duration ;

pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW); // Make sure we drive the pin low…
delayMicroseconds(2);
digitalWrite(pingPin, HIGH); // Pulse high for 5us
delayMicroseconds(5);
digitalWrite(pingPin, LOW); // Finish the pulse…

pinMode(pingPin, INPUT); // Get ready to read…
duration = pulseIn(pingPin, HIGH); // Wait for the echo pulse to drop back to low

// The speed of sound is 29 us per cm… j

float cm = duration / (29. * 2.) ;
dtostrf(cm, 8, 2, dbuf) ;

u8g.firstPage() ;
do {
draw() ;
} while (u8g.nextPage()) ;
}
[/sourcecode]

Addendum: I’ve been snapping short videos with the Vine app, and then posting them to Twitter and Facebook. Irritatingly, these don’t seem to actually play properly when I embed them back in my website. I’ll figure out a better workflow next time.

Addendum²: Goofing around a little, it appeared that this sensor worked out until about 70cm or so, and then snaps to 340cm. Not sure what that is about: the sensor should behave more accurately than that. I’ll experiment more tomorrow. I should also note that these Parallax sensors are fairly pricey: list price is almost $30. I like the Parallax guys a lot, but that’s pretty spendy. You can get much cheaper modules on Ebay, with costs as low as around $1.50. I haven’t got any of these, but they are worth trying, although various sources on the web suggest that you might get what you pay for. Try googling for “HC-SR04” for more information.