sobota 7. února 2015

Future plans for the central node

Lazy day today, I sorted out some components I had laying around in drawers, took a long afternoon nap and played Deus Ex: The Fall. The game isn't bad... just a bit weird, and it looks like I cannot jump... Did someone say "Doom"?
I needed to make the final decision about the central node. I was leaning towards using Arduino Mega or Due, but finally I decided to go the "Raspberry Pi + Arduino Pro Mini" way. That way I'll have the whole communication under control and I can use the code I already have for Arduino, but additionally I'll have access to the processing power of RasPi. If possible, I'll make the RasPi act as a web radio as well, and will let Arduino control the mpd or whatever music program I'll use.
The plan is to have one RF24 module connected to the RasPi directly, and RasPi will act as an internet bridge, using one dedicated channel for nodes that care about getting internet connection. Another RF24 will be controlled by Arduino, communicating with sensors and sending out time info, weather info etc. on another channel. I might actually connect TWO RF24 modules to Arduino,  one running the RF24Network stack, the other just using basic RF24 for reading data from sensors (reason explained below). That sounds as an overhead, but when one RF24 module costs 70 cents... Arduino will also control one RFM12B module for compatibility with other devices at home using these modules, and will also need to support the RS485 interface for the old clock on my wife's bedside table. The clock is about ten years old, before the wireless modules became available and popular, and it's running on PIC!
To recap and write my thoughts down:
  • RasPi
    • RF24 module providing internet access on specific channel, using RF24Ether
    • 2.2" ILI9341 based TFT LCD
  • Arduino
    • RF24 module running basic RF24 radio stack to receive info from sensors
    • RF24 module running RF24Network to communicate with clever nodes (clock, remote displays etc)
    • RFM12B module for older devices
    • RS485 for that old clock
    • IR receiver, control knob etc. for controlling the web radio running on RasPi
I started to build the "baseboard" that will hold all this additional hardware, but I barely finished the power supply and RasPi cable / connector, so no pictures today. I'll work on it tomorrow and post a pic of it when it takes final shape. It's connected to RasPi via flat cable. If necessary, I will be able to flip it over, face-to-face to RasPi, making the whole thing more compact to be put into a small box.
The CR2032 node doesn't perform well. I started it yesterday evening with 2.97V, and in the morning it was still around 2.97V - 2.96V, hovewer, it dropped over day, and while I am writing this, it dropped again to 2.92V. My impression is I am at the end of the discharge curve (meanwhile, the voltage dropped to 2.91V) and the battery is dead. I am puzzled, and wondering if perhaps the whole overhead of RF24Network isn't causing this. It only sent something like one or two hundred of packets! Another node running with just basic RF24 radio stack was running for two weeks without much of power optimization.
Voltage dropped to 2.90V... oh well. I'll let it run and see where it stops - that would be the minimal operating voltage *grin*.

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