Katie :: my take from The Great Internet Migratory Box of Electronics Junk

Title:	my take from The Great Internet Migratory Box of Electronics Junk
Topics:	electronics
Date:	2008-06-13 @ 16:25
Security:	public

my take from The Great Internet Migratory Box of Electronics Junk
Originally uploaded by MissionControl.

Here are the items I took from The Great Internet Migratory Box of Electronics Junk. The only one for which I have a specific project in mind is the numeric LED display, which should be suitable for my remote lakewater temperature monitor project. That's a project I first blogged about a couple years ago and to which I've only given a spare thought since then. For the temperature sensor, I imagine soldering a DS18S20 onto the end of a piece of a cable and waterproofing it with some silicone caulk and heat-shrink tubing. This sensor would be connected to some sort of minimal microcontroller (would an Arduino be overkill?) that would be powered perhaps by solar cell. Besides talking to the temperature sensor, the microcontroller would send temperature readings to some sort of RF transmitter—say, the one from this? Or maybe this is an ideal application for ZigBee? The wireless link should span about 150 feet of lightly forested terrain. At the other end, the receiver should pass on the data to another minimal microcontroller that would also handle the display.

The target environment already has an 802.11b network, though, so if that signal can span the 150 feet and there's enough available power on the transmitting end, I wouldn't need to bother with a dedicated receiver. I suspect this setup might be more expensive, though, for the brains needed on the transmitting end.

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Title:	Untitled
Author:	kaszeta
Date:	2008-06-13 20:33 (UTC)
Status:

If I was doing it cheaply, I'd do Zigbee, it's what I use on most of my wireless sensor projects, and it scales nicely if you want to add more sensors later. I might be able to scare up a non-proprietary schematic and some code at some point.

I've used that Sparkfun RF link. It's tolerable, but make sure you send packets with checksums and the like.

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Title:	Untitled
Author:	barawn
Date:	2008-06-14 22:43 (UTC)
Status:

I know everyone's fawning over Arduinos nowadays, but the Microchip PIC controllers would still be a good choice for this. They're dirt cheap, easy to use, and (for complete silliness) have a really cheap Ethernet interface which you can get as well (you can actually sample all of them from Microchip if you just feel like mucking around first).

Of course, it does raise the question: why not grab a WRT54g, dump something like OpenWrt or DD-Wrt on it, and tap off of the GPIO pins directly (disabling some of the router's LEDs and repurposing them)? Using two or three, you could shove them into a shift register and expand it out to as many bits as you want, or just implement an I2C bus and grab an I2C port expander like the PCF8575.

That solves the connectivity problem right away. If you'd rather add a microcontroller, you could do it by adding a serial port to the wrt54g and communicating serially.

Incidentally, do you have a DS18S20, or was that just a suggestion? Dallas's 1-wire bus is okay, but an I2C-based sensor might open more options. For instance, you could get a combination pressure and temperature sensor - the HP01D or HP02D (depending on if you anticipate the device being deployed on Mount Everest or not) is an I2C-based combination pressure/temperature sensor that needs very few parts - it can technically be done with no parts if you don't mind the conversion taking a little while and generating the clock yourself. It's also like $5-$10 or so from futurlec.com (who are something like the *only suppliers* of it), and comes already in a little DIP interface board.

I've already used the HP02D, so I can actually send you the software for doing the math to actually get out values from it if you wanted. There are a few undocumented tricks with it (like making sure the calibration values are correct when read out). The other nice thing is that since the WRT54g would be running Linux, you could add the I2C bus using the GPIO kernel driver, and not really have to worry about whether you're doing the bus protocol correctly.

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Title:	Software for HP02D
Author:	Anonymous
Date:	2008-07-24 10:09 (UTC)
Status:

I'm struggling with these Hope sensors, so would be an avid reader of any details and/or code that you (barawn or katie) are willing to post (or contact me at hilderbuild.com). Cheers

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