Raspberry Pi and a PIR Sensor

Today, I successfully used the Human Sensor PIR module with the RPi. I ordered this: http://www.amazon.com/gp/product/B007XQRKD4/

I followed this blog post. The only change was different GPIO port numbers:
http://www.millamilla.com/?p=18

When moving in front of the sensor, the LED turns on.

Worked great!

There are two manual adjustments on the module:

• Sensitive Setting: turn to right, distance increases (about 7m); turn to left, distance reduces (about 3m)
• Time Setting: turn to right, time increases (about 300 seconds); turn to left, time reduces (about 5 seconds).

Raspberry Pi and Temperature Sensor

Today I successfully connected the DS18B20 temperature sensor to the RPi. I ordered the waterproof version that comes with ~ 2 ft leads.

I used the following Adafruit lesson to the letter and it worked great:
http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing/overview

RPi - Controlling a Servo Motor

Today I set up the Raspberry Pi to control a servo motor.

For the hardware setup, I referred to chapter 10 from the Raspberry Pi Cookbook. Aside from the Pi, I only used the Pi Cobbler, a 1k resistor, and a 4AA battery pack. I didn't use any other special components. In the future, I'll consider getting a specialized breakout board for controlling servos.

For the software, I started with the code from this blog post:  http://www.doctormonk.com/2012/07/raspberry-pi-gpio-driving-servo.html
Note that in Simon Monk's post, he uses a transistor in his circuit that I didn't use based on the circuit in the book.

My first attempt didn't work well. The servo would turn very slowly, arriving at the 180 degree position, and stay there. I could feel the motor working but there was little to no movement.

After further research, I made some modifications to the starting code including changing the order of the True and False statements and playing with the timing. Things started to work. I was reading that servos needed between a .001 and .002 second pulse to move between 0 and 180 degrees respectively. I was finding those to be too long. For my servo, the range was between .00055 and .002. I don't know if that is a servo thing or if that helps to compensate for a delay from the RPi itself.

Finally, I added some code to accept an angle 0-180 as input and convert that angle into the appropriate timing of the pulses. I also had that input affect the number of loops because for shorter angle changes, a greater number of loop iterations would result in the motor jumping around slightly after reaching the desired angle. Now I can probably convert this to a function and use with other programs.

I had been reading about others experiencing a jittery movement when only using GPIO to control the servo but once I figured out the appropriate timing and loops, I found that it moved very smoothly. I don't know if there are other factors that I'm not experiencing that could affect the performance.

The Code:

import RPi.GPIO as GPIO
import time
import math

pin = 18
refresh_period = 0.02

prev_angle = 90           #initiate previous angle

GPIO.setmode(GPIO.BCM)

GPIO.setup(pin, GPIO.OUT)
GPIO.output(pin, False)

while True:
    angle = int(input('Angle: '))

    # convert degrees (0-180) to the servo pulse (.00055 to .002ms)
    pulse = (angle * .00000805555) + .00055

    # determine the number of loops based on degrees needed to travel, a shorter distance (degrees) to travel = fewer loops
    loops = math.ceil(math.fabs(prev_angle - angle) * .135) + 2
    prev_angle = angle

    # move the servo arm
    for i in range(1, loops):
        time.sleep(refresh_period)
        GPIO.output(pin, True)
        time.sleep(pulse)
        GPIO.output(pin, False)

The circuit:

The servo I used:

The servo specs:

Years ago, I created a very simple robotic arm that waves and was able to revive it once again with the RPi!

RPi - Python and Blinking LED

I successfully created a python script to blink an LED attached to the RPi/Pi Cobbler.

The circuit attaches to the 3.3V output, routes through the LED, a 470R, and back to GPIO pin 18.

I wrote it using IDLE on the RPi GUI.

I used this blog post as my guide: http://www.thirdeyevis.com/pi-page-2.php
I also referred to this one and even started to set up the WebIDE: http://www.akeric.com/blog/?tag=pi-cobbler

The code:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

def Blink(numTimes,speed):
    for i in range(0,numTimes):
        print "Iteration " + str(i+1)
        GPIO.output(18,True)
        time.sleep(speed)
        GPIO.output(18,False)
        time.sleep(speed)
    print "Done"
    GPIO.cleanup()

iterations = raw_input("Enter total number of times to blink: ")
speed = raw_input("Enter length of each blink(seconds): ")

Blink(int(iterations),float(speed))