Electrickiness.

I did an electronics day today.

1. All the 1-wire stuff was connected to a bare board that was just sitting on top of the wiring cabinet.

Today, I installed a 24-port RJ45 patch panel, punches all the cables into said panel (and all the other unconnected cat5 that was also there), milled suitable opening into a polycarb box, installed board, and connected it up with short cat-5 patch cables. MUCH neater.

2. When the garden was done, they also installed a couple of solenoids to control the irrigation. 24VAC. After months of ignoring them I finally connected to up today.

Thinking that nothing quite succeeds like serious over-kill, I went a little wild:

• Bought 24VAC wall wart.
• Built 15V DC supply for a CPU board I had lying around. The supply was just normal bridge rectifier => capacitor => LM7815. Nothing special as it's feeding a DC-DC convertor on the CPU board. (Which annoyingly has an absolute max rating of 20VDC otherwise I would have skipped the regulator).
• Realized that regulator on supply was doing to dissipate around 4 watts, and the LM7815 has a 65 degree/watt resistance to air, so maybe a heat sink would be required.
• Milled heatsink. Nothing quite like 1/3rd of a kilo of aluminium to cool a 1.6 gram part.
• Milled appropriate openings in polycarb case.
• Connected up solid state relays. This was the gamble part: The NGW100 CPU board is specified for 8mA maximum current output on the general purpose I/O pins, and I wasn't sure what the solid state relay would require. I win! when I measured it off the lab power supply, tt turns out the relay uses 300uA @ 3.3VDC. Neat!
• Wired everything together.
• Crossed fingers.
• Powered up. Worked first time. :) I had a few "WTF?" moments when testing it, because output from the CPU board needs some load to go to a sane value. Likewise the solid state relays. So poking at things w/ no load and a multimeter generated a few seconds of puzzlement until I started at 100k resistors everywhere.

So now I have a functioning linux machine on the network, running a web server, so it can control 2 bits of output. Yay overkill!

3. And I fixed up the touch-screen computer to run totally off read-only flash and ram disks. This is an attempt to make it ultra stable. (It boots to the point of being able to login to it over the network in less than 1 second from power on :)

This was actually painful and frustrating as the lcd screen for this computer is controlled by an FPGA. And so when I stuff up the boot process, there is no indication of why. Lots of going back and forth with SD flash cards.

4. And now I'm off to write a pygtk widget to hook up this up to buttons on the touchscreen.

And feeling rather pleased with my productivity today. Managed to actually _shrink_ my todo list today!