Sensor Array and Monitor




Introduction: Sensor Array and Monitor

About: I am an Electrical Engineer with over 30 years experience in my field. My hobbies include making things and fixing things. I enjoy making things with Arduino's, and making useful things with 3D printing. Oth…

The Sensor Array and Monitor is a wireless monitor with motion sensors. This system features multiple sensors that detect motion and a monitor to display the sensor hit count. The monitor is small enough to fit in a pocket, and vibrates to alert you when the sensors are active.

The sensors work independently from the monitor. Each sensor must be within radio range of at least one sensor, or can be in range of several or all sensors. When the PIR detects motion, it transmits that sensors total number of hits. When another sensor receives this report, it relays this report and adds it's total number of hits to the report. In turn, each sensor does the same until all sensors hear the same report, and transmissions will stop.

The monitor listens in on the sensor transmissions and displays each sensor hits on the display. When sensors are transmitting, the monitor vibrates. When the sensors are not active, the report button sends a signal to the sensors to report their hits. The monitor has a reset button to signal the sensors to reset the hit counters to zero. The monitor only needs to be in range of one sensor to track hit counts on all sensors, or send commands to all sensors. When the monitor is powered on and in range of any sensor, the monitor will keep track of all sensor hit counts. The last sensor to change will flash green. The monitor will color the sensor text red when the sensor reports and is in range of the monitor. After 5 minutes of sensor inactivity, the monitor display will turn off to save power.

Step 1: The Monitor

Monitor Components:

1 - Adafruit Feather 32u4 Radio with RFM60HCW Packet Radio

1 - Adafruit 1.44" Color TFT LCD Display

1 - Lithium Ion Polymer Battery 3.7v 1200mAh (Adafruit)

1 - Vibrating Mini Motor Disc (Adafruit)

2 - momentary contact buttons

1 - SPDT Slide Switch (Adafruit)

The case is 3D printed and information, files and assembly instructions can be found here:

The case features a integral 3D printed circuit board. Note the wiring diagram is shown from the back side of the device.

Step 2: The Sensors

Sensor Components:

1 - Adafruit 5V Pro Trinket

1 - Adafruit RFM69HCW Transceiver Radio Breakout

1 - PIR Motion Sensor (From Adafruit)

1 - 8 AA Battery Pack (Radio Shack) - two rows of 4 batteries with 9V type battery clip

1 - 9V type battery clip

Male and Female Header Pins (0.1 in)

The case is 3D printed and features a 3D printed circuit board, battery door, and PIR sensor sun shield. The files and assembly instructions can be found here:

The circuit board wiring diagram shown is from the back of the board.

Step 3: The Code

There are two sets of code, one for the sensors and one for the monitor.

Change this line for each sensor:

#define NODEID 1

Each sensor needs a unique number starting with 1 to 4.

example, for sensor 2:

#define NODEID 2

Step 4: Additional Comments

I have found the PIR sensors are affected by radio transmissions. If a radio transmitter is near the PIR, it will cause false triggers. The Sensor sketch ignores the PIR when transmitting, so this is not a problem for normal operation. If two sensors are close together, they may interfere with each other. Separate the sensors by at least 5 feet to avoid false triggers from other radios.

The Sensor battery pack used is a tight fit. Insert the battery pack top first, then slide in the bottom. Reverse the procedure for removing the battery bottom first. If you use another battery pack, you may need to modify the battery compartment. The sensors do not have an on-off switch, so the battery pack needs to be unplugged to turn them off. I put a small strip of paper between one of the batteries and the terminal to shut them off, then I can just pull the paper strip out to turn it on.

Direct sunlight on the sensor lens will cause false hit. The sun shield on the PIR will help shield the sensor. When setting up the sensors, aim the sensor away from the rising or setting sun.

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    5 years ago

    Great Project!

    I prototyped this project, but for the base the lcd displays on for a couple seconds when powered up. Then its blank. When I press either of the two buttons, the lcd displays for a couple seconds then turn off.

    Any ideas?


    Reply 5 years ago

    Sorry I didn't see this sooner. The display will go blank to save power when there is no activity received from the sensors. When the monitor receives radio traffic from the sensors, it will turn on.


    5 years ago

    Nice Instructible. Can you give me a rough idea of cost of sensor and main unit?


    Reply 5 years ago

    Thanks. I estimate the total cost of components for this project is about $220. The costs may not cover filament or shipping costs. I used a good part of a roll of PLA filament in development. It may be about a half roll if I did another set now. Most all components can be purchased at Adafruit ( except for the sensor battery holder. I got mine at Radio Shack. I'm sure they can be also found on Amazon. The formatting allowed for comments doesn't allow tables. The attachment shows a better cost breakout.

    - Dave

    Sensor Array Proj Cost est.JPG

    Reply 5 years ago

    Thank you for the reply and the pricing information. It is a nice project and you wrote a nice Instructable.