Turn Your PC Into a Motion Sensing Security Device with .NET
Thanks to new types of hardware that can easily be programmed using .NET, you can create a
motion sensing application that can be deployed for security—or just for fun.
by Wei-Meng Lee
on how to integrate your .NET applications with external devices, I showed how to
display system information using an LCD display. In this article, I will dive into the world of sensors. Sensors
are interesting devices because they are the "eyes and ears" of your computer and can provide detailed
information about the surroundings, such as temperature, lighting detection, proximity measurement, and so
For this article, I will be using two types of sensors: a passive infrared (PIR) sensor and an ultrasonic sensor.
PIR Sensor from Parallax
) is a low-cost sensor ($7.95) that is able to detect motion by
using the principle of infrared radiation. It can detect motion up to a range of 20 feet. Its connection is a simple
three-pin connector—GND, 5VDC, and a signal line. When motion is detected, the signal line will register a 1,
and will fall to 0 when the motion stops. It is ideal for detecting movements.
The second sensor, the
PING))) Ultrasonic Sensor
), is much more interesting and it is able to
provide precise measurement of distance ranging from 2 cm to 3 meters. It works by emitting a short
ultrasonic burst and then measures the time it takes the burst to bounce back when it hits an object. By timing
this process, it is able to calculate the exact distance between the sensor and the object. The PING))) sensor
costs $24.95. Like the PIR sensor, the PING))) sensor has a three-pin connector—'GND, 5VDC, and a signal
line. The signal line will return the distance measured in pulses (more about pulses later in the article).
Connecting to the PC
Unlike the LCD module that I discussed in my last article, the two sensors in this article cannot be directly
connected to the RS-232 serial port of the PC. PC serial ports works on RS-232 voltages and serial
communication, while the PIR and PING))) sensors run at 5V (TTL) and uses Pulse-Trigger and Pulse-Width
to trigger. Hence, you need a microcontroller to connect to these two sensors; the microcontroller can return
the results back to the PC via a serial connection.
For this purpose, I used the
BASIC Stamp 2 (BS2) Module
, also from Parallax. The BS2 is a microcontroller
that runs at 20MHz and can execute approximately 4000 instructions per second. The BS2 costs $49.
You also need a board to house the BS2 module. I used Parallax's USB
Board of Education (BoE)
. The Parallax PIR sensor is shown.