Page 137 - Programming the Photon Getting Started With the Internet of Things

Figure 6.13 Reading temperature from the Photon.

Measuring Distance Using an HC-SR04 Sensor

This experiment includes the use of an HC-SR04 ultrasonic range finder to detect the
distance from certain objects, as well as being used as a motion detector to determine
when something gets too close. These sensors are more commonly used in robotics to stop

the robot from bashing into objects. The ultrasonic sensor sends out pulses every so often
using one sensor, and the other sensor reads the feedback of those pulses and determines,
based on the timings in between, how far away an object is. This works on the same
principle as echolocation, which is how bats are able to see at night or how dolphins can

detect their surroundings. For this experiment we are going to use the components listed in
Table 6.4.

Schematic Reference Description Appendix

M1 Photon board M1

Breadboard H1

Jumper wires H2

H1 HC-SR04 M2

Table 6.4 Components and Hardware

The ultrasonic range finder used for this experiment has four pins. Two of the pins are
for 5-V power and ground; the other two pins are labeled trigger and echo. When the
trigger pin is activated for a very short period, it sends out pulses of ultrasound. When the
pulse is returned to the range finder the echo pin will indicate this. The breadboard layout