The next step in this adventure was to find a way to rack mount all this kit - I was fine with the sensor pods hanging loosely at the top of the rack but the Pi and connector board needed to be mounted neatly. The sensor pod boards then connected with an RJ12 cable knocked up using some spare lengths of cat5e. Once assembled each connector board presented four RJ12 ports, and connected to the Pi's 3V, 5V, Ground and 4 of the GPIO pins. The PCB back from the printers, I managed to fit 8 main boards and 24 pods in to the A3 sized board.
I knocked up the boards in Circuit Wizard and sent them off to a PCB printing company. Using four RJ12 ports on each connector board I could then plug up to 4 pods in to each Pi (although in practise it became unreliable when more than 3 were plugged in, presumably I was trying to draw too much power out of the Pi). I then designed a connector board to sit between these pods and the Pi. This worked great so I moved onto the next step and came up with the idea to create "sensor pods" - small circuit boards containing the DHT11 sensor, some sort of connector and an LED. The prototype for this system was a single DHT11 sensor on a breadboard, connected to a Pi's GPIO pins. Mechanism to send SMS messages if the temperature rises above a defined limit.PHP script on the web server to receive the data and log in a MySQL database and also to display the current temperature and humidity at each sensor.Python script on the Pi reads the temperatures on a schedule and uploads this data to a web server.Use a Pi to monitor temperature but reduce the number of Pis needed to a minimum - so if we have 3 racks in one room, try and monitor these off a single Pi.I've recently had a photo from this pop up in my Facebook memories so decided I'd dig out the write-up I did and post it on my blog.
Main components on the bench before putting into the racksīack in 2015 I was looking for a cheap way to monitor the temperature in our server racks and also for a project with my new Raspberry Pi Model B. By Katy Nicholson, posted on 25 March, 2021
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