RobotSentry – Home Security System – Part 2


Following on from RobotSentry – Home Security System – Part 1 this is the second post in my security system project. With the basics of the design finished I assembled a set of components. Many of them I was able to salvage from previous projects.

Here is a list of all the items I used :

Photo Item Source Notes
Raspberry Pi 2 Model B Raspberry Pi Farnell Model B+
DC-DC Step-down regulator Voltage regulator eBay 12V to 5V (variable)
2 Channel Relay Module 2 Channel Relay module Amazon 2-channel module
Silver IR Illuminator 1 2 Infrared Illuminators Amazon 12V, 48 LED
Pi NoIR Camera Module PiNoIR Camera CPC Infrared Camera
BH1750 Light Sensor Module BH1750 I2C eBay I2C Light sensor
BMP180 Pressure Temperature Module BMP180 eBay I2C Temp pressure sensor
PIR Module #1 PIR module Amazon
Junction Box Enclosure 175x151x95mm CPC Plastic IP65
Junction Box with Transparent Cover Enclosure 80x172x53mm CPC Hylec, Plastic IP67
 12V DC Power Supply 12V Power supply CPC 3.5A
20m Cat5e network cable CPC
Pi camera 50cm cable eBay
5mm LEDs CPC

To connect it together I also needed these bits :

QTY Item Source Notes
2 330 ohm resistors CPC
3 2.1mm DC barrel sockets CPC For illuminators
2 2.1mm DC extension cables CPC For illuminators
1m 40 way ribbon cable eBay
4 2×20 IDC connectors eBay
2 Stripboard eBay
200 2.54mm male pin headers eBay
19 2.54mm female pin headers eBay
2 2.5mm nylon bolts eBay
12 2.5 nylon round pillars eBay
4 4mm nylon hex pillars eBay

I used a variety of suppliers but the components (or alternatives) are available from various other sellers.

Here is a photo of the external box with a ruler included for scale :

RobotSentry External Sensor Box

You can see (from left to right) the light sensor, pressure sensor, LEDs, PIR and camera module. This box has a clear plastic lid. This week I carried out a few tests with the PIR sensor. I had planned to mount it inside the and let it look through the transparent cover. However I found it just didn’t work behind the plastic. So this week I will cut a hole in the transparent enclosure cover and mount the sensor. The join can be sealed with silicon sealant. The camera module will be stuck to the cover and remain protected inside the box.

Here is a photo of the internal box :

RobotSentry Internal Box

The black pin headers on the strip board are for the ribbon cable that connects to the sensor box. The barrel connectors in the top left and right will be connected to the relay module to provide power to the infra-red illuminators.

Here is a close up of the 12V to 5V regulator and 2-channel relay module which are mounted on the side :

RobotSentry Internal Box

Coming soon

The next posts in this series will be :

  • RobotSentry – Home Security System – Part 3 – Hardware Testing
  • RobotSentry – Home Security System – Part 4 – Installation Outside
  • RobotSentry – Home Security System – Part 5 – Working System!


  1. Hi Matt. Great series so far. I also coincidentally am working on a very similar system (RPI2, LED IR array, Noir Camera, PIR sensor, 2 channel relay, all powered via 12V DC to IR LEDS, and UBEC stepped down to 5V DC for the RPI). My design is intended to separate the camera, PIR sensor and IR LEDS into an outdoor (driveway) housing connected an indoor (garage) RPI control unit via a HDMI/Camera extension cable. The hardware setup for my outdoor camera housing needs some kind of adjustable mount for the camera, but I’m working on it. I’ve tested the system all wired up and it appears to work discretely. I’m now trying to work out the software design for a PIR triggered monitoring solution. Do you have any recommendations on the best approach to handling image/video capture? e.g. a single Python application which loops waiting for PIR, flipping the IR LED relay, capturing an image, repeat. Or has your previous project experience pushed you in a different direction? Thanks and I’m looking forward to your future instalments.

    • Just a quick follow up with my build. I found with 12V DC @ 2 Amps simply didn’t provide enough juice for just 1 of those 12 V DC IR LED arrays + the RPI. I switched to a 3 Amp power supply and its better, but not ideal. With your 3.5 Amp power supply, it would probably drive just 1 of your IR LED lights brighter than 2 units. The problem is those IR LED arrays need like 12V DC @ 2 Amps to themselves to perform reasonably unless you’re in a smallish room. With the RPI + accessories, I think you’ll find the IR lighting to be unsatisfactory.

      I’m about to pull the trigger on ordering a 5 Amp power supply myself. Even if its over kill, the power supply will run cooler when everything is drawing simultaneously.

      • Thanks for the info. My plan was to get the system working without the IR lamps, check the relays switched ok and then introduce the lamps as required. So I might just need to keep an eye on the power consumption. I’ve got a conventional security light as well in the same area so I won’t know if I even need two IR lamps. Luckily I can always upgrade the power supply if I need to.

    • It’s still on my list but I’ve got so many other things getting in the way I’m struggling to make progress with it.

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