Session 3 of the AFNOG tutorial
on IoT sensors

Uli Raich

• the ultra-sonic sensor
• the color sensor
• the colored paper

• cylinders
• boxes
• a sphere

It is more difficult to insert these into the TWiki pages than into the slides.

I uploaded mpeg video clips and added links such by clicking them

you can download and/or visualize the clips.

VPython creates the scene in a separate windows and

• Lets you move the viewpoint (3rd mouse button)
• Lets you scale the image (2nd mouse button)

and here is the video clip:

https://iotworkshop.africa/pub/AFNOG/VPythonAndTheVirtualWorld/virtualWorld.mpeg

You can find it at vpython.org

Now we will go through a few simple examples which will enable us to assemble the scene.

It turns out that I did not have this problem on my older version of

Raspbian which runs a slightly older version of Python.

It must have appeared only with a very recent Python-2.7 version.

It is only a warning and does not prevent the program from running.

If it annoys you, you have 2 options:

• Correct the code of VPython or
• simply suppress the warning

change the color of the sphere and make it real small.

simulating the paper sheet:

(depending of the distance of the real paper to the distance detector)

and how to change its color (depending on the color found by the color sensor)

Let's first do this without reading the sensors by just displaying the paper at a certain

position before moving it on and by changing its color and displaying it for a time before

changing it.

https://iotworkshop.africa/pub/AFNOG/VPythonAndTheVirtualWorld/movePaper.mpeg

https://iotworkshop.africa/pub/AFNOG/VPythonAndTheVirtualWorld/colors.mpeg

https://iotworkshop.africa/pub/AFNOG/VPythonAndTheVirtualWorldlabel.mpeg

First the blue base plate is creates on which we have 2 cylinders

representing the loudspeaker and the microphone.

On top of each white cylinder I put a very thin black cylinder.

In addition we see the quartz implemented as a box

Understanding this code will allow you to easily create the model of the color sensor.

• Create a pi object connecting our program to the pigpiod daemon
• Create a colorSensor instance
• Create a usSensor instance (us stands for ultra-sonic)
• Calibrate the colorSensor with black and white

• Read the distance sensor
• If the paper is close to the distance sensor, read the color
• Adapt the distance and the color of the model paper

The color found by the sensor depends on the light intensity

reflected by the paper and this changes with distance

If we measure the color far away from the sensor little light will fall

onto the sensor and the color will come out dark.

Therefore put the paper close to the color sensor at first and keep the same

color when the paper is moving away from the sensor.

It is time to experiment. Hopefully you now have the information needed to play with

• the Python language
• sensors and actuators
• VPython to create realistic models

The Raspberry Pi offers you many more possibilities:

• different hardware interfaces
  • I2C bus
  • SPI bus
  • camera interface ....
• and of course you can write your IoT code in a different language