Distance sensor with a threshold

Author: cs223vr

Table of Content

Distance sensor with a threshold
- Introduction
- Objective
Tutorial

Introduction

This project is about warning the user if an object is above/below a certain threshold, using a distance sensor (HC-SR04) and a buzzer (PKM22EPP-40). The distance measurements will be sent over WiFi and will be visualised through pybytes platform. By following this tutorial you will learn how to collect data from a sensor and pass it on to the internet. The estimated time for this project is 2 hours.

Objective

I chose this project because I wanted to work with the distance sensor (HC-SR04). The purpose is to be able to warn the user if the distance to an object increases or decreases. This can be applied in many scenarios, such as monitoring if a door is opened.

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Tutorial

Material

The material used in this projekt can be seen in Table 1.

Table 1 - List of materials

Computer Setup

The integrated development environment (IDE) that was used was Pymakr Plugin for Atom, which is programmed in MicroPython language. Down below is a guide on how to install Atom and the Pymakr Plugin, along with how to connect the Pycom device to your computer and how the code is uploaded to the device.

Step 1:
Download and install Atom, here.

Step 2:
Navigate to the Install page, via Atom > Preferences > Install and search for Pymakr and install the official Pycom Pymakr Plugin.

Step 3:
Connect your Pycom device to your computer via USB. Pymakr has auto-connection enabled by default and in case your device hasn’t connected right away, click on Connect device and then on your device.

Step 4:
To upload the code, click on "Upload project to device", as shown by the red rectangle in Figure 1. The code for this project can be found under The code-section

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Figure 1 - How to upload the code to the Pycom device.

Putting everything together

This section describes how all the electronics were connected.

The breaboard was connected to the expansion board with two jumper wires, one to 3V3 (power) and one to GND (ground), which is shown by (1) and (2) in Figure 2. The Pycom LoPy4 was also attached to the breadboard.

The HC-SR04 were attached to the breadboard and jumper wires were connected the following way:

(3) VCC -> power (+ on the breadboard)
(4) Trig -> P23 (Pin 23 on the expansion board)
(5) Echo -> P22 (Pin 22 on the expansion board)
(6) GND -> GND (- on the breadboard)

where the numbers are connected to the numbers in Figure 2.

The PKM22EPP-40 was also attached to the breadboard with one jumper wire connected to P21 (7) and one to GND (8).

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Figure 2 - Assembly of components.

Platform

In this project, the free cloud-based device management platform Pybytes was used, which is available for all Pycom development boards and modules. On Pybytes, you can add your device via USB and keep your devices connected to your favourite network and monitor them in a easy dashboard.

The code

The code for this project is presented down below and consists of two functions. A main-function that is looping forever, and checks if the distance is above the threshold or not. If the distance is above the threshold the buzzer is turned on and the distance is sent to the platform, otherwise the buzzer is turned off. The distance-function returns the measured distance from the sensor.



























































# Libraries
import utime
from machine import Pin, PWM
import time

# Setup
echo = Pin('P22', mode=Pin.IN) # HC-SR04 sensor, pin 22
trigger = Pin('P23', mode=Pin.OUT) # HC-SR04 sensor, pin 23
buz = Pin('P21') # PKM22EPP-40, pin 21
tim = PWM(0, frequency=300)
ch = tim.channel(2, duty_cycle=0.5, pin=buz)
threshold = 10;

# Main function
def main():
    while True:
        distance = distance_measure() #Get measured distance
        time.sleep(2)

        #Check if the distance is below threshold or not
        if(distance > threshold):
            ch.duty_cycle(0.50) # Turn the buzzer on
            pybytes.send_signal(1, distance) # Send distance to platform
        else:
            ch.duty_cycle(0) # Turn the buzzer off


# Distance function
def distance_measure():
    # Make sure output is low
    trigger.value(0)
    utime.sleep_us(10)

    # Trigger 8 cycle sonic burst by setting trigger to high for 10us
    trigger.value(1)
    utime.sleep_us(10)
    trigger.value(0)

    # Wait for pulse to start on input pin.
    while echo() == 0:
        pass
    start = utime.ticks_us()

    # Run until input pin changes to low.
    while echo() == 1:
        pass
    finish = utime.ticks_us()

    utime.sleep_ms(10) # wait before the next measuring

    # Calc the duration of the received pulse, divide the result by
    # 2 (round-trip) and divide it by 29 (the speed of sound is
    # 340 m/s and that is 29 us/cm).
    distance = utime.ticks_diff(finish, start)/29/2


    return distance

Transmitting the data / connectivity

To send data to the Pybytes platform, the function pybytes.send_signal(signalNumber, value) is called. This function is part of the Pybytes library, and it has two arguments: signalNumber and value. The signalNumber represents which signal is receiving data and the value is in this case the distance measurements.

The choice of wireless protocol was WiFi and the data was sent every time the measured distance was above a certain threshold.

Presenting the data

In Pybytes, you can define the signal and visualize the data in a dashboard, which is shown in Figure 3.

Figure 3 - Dashboard in Pybytes.

.
Here you can see when the data was received and how many bytes that was sent. You can also visualize the data with different charts, as can be seen in Figure 4.

Figure 4 - Line chart with received distances.

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The figure represents what time the data was received along with the measured distance.

Finalizing the design

Figure 5 shows the final result of this project.

Figure 5 - Pycom device and sensors

There have been no difficulties during the course of the project and by following this tutorial you should have learned how to collect data via a sensor and pass it on to the internet.
An improvement that could have been made is to send fewer bytes as 8 bytes are currently being sent, which is a bit much. LoRa could also have been used instead of WiFi since it enables transmission of data over longer distances and has low energy consumption.