1202 ALARM

I finally got around to finishing off this prototype 7-segment display module, based on the MAX7219 integrated circuit. I went for the largest displays that the IC can drive directly, but that meant wiring them all together. I've since acquired a slightly smaller 4-digit display which will be a lot easier to wire up. My home brew Arduino is,driving the module, but there are libraries in JAL for PICs for the MAX7219 as well as for the Arduino. The interface is a simple SPI type and could be driven from the Raspberry Pi except that the 3.3v/5v issue becomes a pain in the rear as usual. I'm keen to have this bad boy on the dashboard of the MR2 sometime soon.

First of all, I invested £7 in a micro wi-fi dongle for the RaspberryPi, which you can just about see in the photo above plugged into the upper USB port.  It is low-power and very low-profile and makes the RaspberryPi server very neat.  For basic temperature sensing, all that would be needed would be a 4-core cable from the LM75 sensor to the RaspberryPi and 5-volt power and that would be it, a device that can log and send data from anywhere within range of a wi-fi access point. Now, it dawned on me last week (luckily after only 3 hours) that I was writing a small file out to the SD card every 5 seconds from my Python program which might be hard on the SD card with all those writes.  SD cards and Linux file systems provide some sort of wear levelling, but any application which writes intensively to the card is going to wear it out fairly quickly.  Writing to the card every 5 seconds might wear it out in a few weeks at best. There are 2 possible solutions, which seem suited to dif