Editing Eyes in the back of your back
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[[User:rachel|Rachel]] and others are creating a vest that will allow the wearer to feel side-to-side movement behind them. This will be done by a set of motion sensors connected to a touch display (of pager motors, at least initially). The first prototype will have a one dimensional display so that up & down motion will not be detected, but this can probably be added later once some of the more pressing problems are solved. We have not yet made a final determination on the prototype sensors but have had some success with ultrasonic rangefinders. | [[User:rachel|Rachel]] and others are creating a vest that will allow the wearer to feel side-to-side movement behind them. This will be done by a set of motion sensors connected to a touch display (of pager motors, at least initially). The first prototype will have a one dimensional display so that up & down motion will not be detected, but this can probably be added later once some of the more pressing problems are solved. We have not yet made a final determination on the prototype sensors but have had some success with ultrasonic rangefinders. | ||
== Current Status == | == Current Status == | ||
Some functional if rough arduino code for a Parallax Ping))) module has been produced. It blinks an LED once per half second, with a larger duty cycle the closer an object is to the sensor. The Ping))) module is large and somewhat cumbersome, and appears to be quite inaccurate at distances greater than about 2-3 feet. There is a pair of MaxSonar-EZ1 modules in the Cyborg parts bin which look interesting to try as well. | |||
I (Rachel) have a fairly detailed mental model of the armature but have not made it yet. | |||
Code: | |||
<pre> | |||
/* | |||
* Based on code found at http://arduino.cc/en/Tutorial/Ping | |||
*/ | |||
int pin = 13; | |||
int pingPin = 12; | |||
int ledPin = 11; | |||
double periodFactor = .5; // percent of one second | |||
void setup() // run once, when the sketch starts | |||
{ | |||
// pinMode(pin, OUTPUT); // sets the digital pin as output | |||
Serial.begin(9600); | |||
pinMode(ledPin, OUTPUT); | |||
} | |||
void loop() // run over and over again | |||
{ | |||
long duration, inches, cm; | |||
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds. | |||
</ | // We give a short LOW pulse beforehand to ensure a clean HIGH pulse. | ||
pinMode(pingPin, OUTPUT); | |||
digitalWrite(pingPin, LOW); | |||
delayMicroseconds(2); | |||
digitalWrite(pingPin, HIGH); | |||
delayMicroseconds(5); | |||
digitalWrite(pingPin, LOW); | |||
delayMicroseconds(2); | |||
// The same pin is used to read the signal from the PING))): a HIGH | |||
// pulse whose duration is the time (in microseconds) from the sending | |||
// of the ping to the reception of its echo off of an object. | |||
pinMode(pingPin, INPUT); | |||
duration = pulseIn(pingPin, HIGH); | |||
// convert the time into a distance | |||
inches = microsecondsToInches(duration); | |||
cm = microsecondsToCentimeters(duration); | |||
Serial.print(inches); | |||
Serial.print("in, "); | |||
Serial.print(cm); | |||
Serial.print("cm"); | |||
Serial.println(); | |||
pwm(duration); | |||
} | |||
void pwm(long microseconds) | |||
{ | |||
Serial.print(microseconds); | |||
Serial.println("ms"); | |||
long offCycle = microseconds / 18; | |||
long onCycle = 1000 - offCycle; | |||
digitalWrite(ledPin, HIGH); | |||
delay(onCycle * periodFactor); | |||
digitalWrite(ledPin, LOW); | |||
delay(offCycle * periodFactor); | |||
} | |||
long microsecondsToInches(long microseconds) | |||
{ | |||
// According to Parallax's datasheet for the PING))), there are | |||
// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per | |||
// second). This gives the distance travelled by the ping, outbound | |||
// and return, so we divide by 2 to get the distance of the obstacle. | |||
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf | |||
return microseconds / 74 / 2; | |||
} | |||
long microsecondsToCentimeters(long microseconds) | |||
{ | |||
// The speed of sound is 340 m/s or 29 microseconds per centimeter. | |||
// The ping travels out and back, so to find the distance of the | |||
// object we take half of the distance travelled. | |||
return microseconds / 29 / 2; | |||
} | |||
</pre> | |||
== Next Steps == | == Next Steps == | ||
Next we'd like to see if the MaxSonar-EZ1 device has any better of a range than the Ping))). Someone else has hooked it up to an arduino and posted code: http://www.flatline.net/journal/2007/12/02/arduino-reading-the-maxbotix-ultrasonic-rangefinder/ | |||