This document provides instructions for extending a simple wind meter to an Internet of Things device by interfacing it with a smartphone. It discusses: 1) Building the mechanical structure of a propeller-based wind meter and coupling it to a DC motor to generate a voltage output proportional to wind speed. 2) Adding electronic components like a resistor and wiring to match the motor's impedance to a smartphone audio input. 3) Creating a mobile app to record the voltage signal from the wind meter and convert the readings to values like rotations per minute and wind speed.

1. Extending wind meter to an IoT device
Architecting of IoT
CHM College - Internet of Things - Session 5
Compiled by - Deepak
malani.deepak@gmail.com
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2. Learning Objectives of this session
1, Building a simple mechanical structure of propeller
2, Extend above to an electro-mechanical device
3, Understand electrical interface of sensors with mobile phones
4, Interpret electrical voltage values
5, Learn to solder electronic components
6, Learn calibration of electro-mechanical instrument
6, Build mobile application to display and transmit data
Disclaimer: Some of the images used here are downloaded from WWW for fair and educational purpose.
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3. Recap: Wind meter (A)
Propeller connected to motor, used as dynamo
Voltage output at motor terminals
Voltage range = 0-40mV
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4. Recap: Wind meter (B)
Voltage output at motor terminals
Reading (mV) Interpretation (wind speed)
0 not moving / stationary
3.4 very slow
5.7 slow
28.2 very fast
19.5 fast
-5.6 opposite direction, slow 4

5. Recap: Wind meter (C)
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Rotary
spoons
structure
Coupling
with toy
dc motor
DC Motor
as
dynamo
Record voltage
with digital
multimeter

6. Sample voltage signal
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7. Wind meter - Interface with smartphone
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Rotary
spoons
structure
Coupling
with toy
dc motor
DC motor
acts as
dynamo
Dynamo
output voltage
characterisation
Impedance
matching
for use as
line-in
4-terminal
TRRS-AUX
connector
Connect with
smartphone
Record with
voice recording
app
App to calculate
and display rpm,
speed values

8. Terminology: Audio connector
3.5mm connector
Auxiliary - AUX connector
Three types
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9. TRRS connection standard for smartphone
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10. Microphone input voltage specification
Typical electret microphone output voltage range = 0-200mV
Smartphone mic-input voltage saturation limit = 50mV
Mic-detection, Impedance matching
Phone detects mic is connected, if phone finds an impedance of about 1600 ohms
on mic-input terminal
Impedance matching of dynamo is done by connecting 1.5ohm resistor in series
with motor
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11. Electronic components and tools needed
Male stereo connector (1pc)
TRS to TRRS adapter cable (1pc)
1.5k ohm resistor (1pc)
10cm long multi-strand wires, red and black (1pc each)
Heat shrink sleeve 3mm (10cm)
Hot air gun or hair dryer (1 unit)
Soldering kit (1 set)
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12. Electronic components and tools needed
Heat shrink sleeve, 10cms, 2mm dia,
Hot air blower (hair dryer)
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13. Electronic components and tools needed
Soldering kit
Wire stripper
Solder lead wire (70:30)
Solder iron (25W)
Solder stand
Sand-paper
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14. 1, Make 5x1cm cut-pieces from heat shrink sleeve (HSS)
2, With sand-paper, sand/rough up the metal leads of resistor
3, Insert one HSS into each leg of 1.5K resistor
4, Solder any one end of 1.5K resistor to one terminal of motor
5, Cut, strip and solder one end of red wire to open end of 1.5K resistor
6, Cut, strip and solder one end of black wire to the other open terminal of the motor
7, Insert two HSS into black wire
Electronic assembly of interface
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15. 8, Sandup the metal leads of the stereo connector
9, Solder the open end of black wire to the smallest terminal (R) of the male stereo
connector
10, Insert last HSS into red wire
11, Strip, solder the open end of red wire to the biggest
terminal (S) of male stereo connector
12, Using hot-air blower, shrink all all the sleeves. Do not overheat.
13, Insert stereo connector to the TRRS adapter cable
Electronic assembly of interface
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16. Assembly sequence
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17. Assembly sequence (continued)
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18. Testing with Voice recorder app
1, Connect the wind-meter with the audio jack of smartphone
2. Most android smartphones will show head-set icon in notificitaion area, as soon
as this device is connected
3, If Impedance matching is done, head-set icon is seen, else only head-phone
icon is seen (PS: iPhones don’t show any icon, but this device is tested on iPhone)
3, Use voice recorder app, record the voltage signal when the rotary structure is
moving
4, Playback voice recording to confirm the signal and change in speeds
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19. Assignment 6
1, Build an android app to visualize and record wind-meter voltage signal
2, Convert the signal values into rpm (rotations per minute) and km/h and m/s by
calibrating wind-meter with a reference anemometer
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