[ale] semi OT: interface

[Byron Jeff]

On Wed, May 25, 2016 at 06:47:40PM -0700, Alex Carver wrote:
> Arduino would work for this application especially if the "smarts" for
> scheduling are put elsewhere (e.g. a larger server that runs cron jobs,
> websites, etc.)

I'm in the process of standardizing my embedded project architecture around
Raspberry Pi Zeros. The combination of the $5 price point per board along
with the standard Linux software platform facilitates using them as
wireless endpoints without additional devices. Honestly, the total cost is
still a bit steep:

$5 RPi Zero
$2.50 USB wireless dongle (I bought a dozen for $30)
$2 USB OTG cable or adapter
$3.50 8GB microSD

gets you to about a $13 price point. I figure that cell phone chargers are
so available as to be thrown in for free.

> 
> RPi would also work but the GPIO aren't as tolerant as the Arduino
> unless you get a hat for the RPi.

Unless it's high speed work, using optoisolators can solve a lot of those
issues. Also RPi GPIOs drive bipolar transistors with no problems. For
driving AC, a optoisolated TRIAC such as a MOT3021/3041 driving a larger
TRIAC should work with no problem. 

What I like about the RPi Zero setup is the fact that by connecting a USB
hub and HDMI, it quickly scales up to a moderate speed Linux workstation
that can be used for development/configuration. Once configured, the zero
can be placed at the project site and then is accessible via ssh or web for
continued development/monitoring.

I started down the ESP8266 path, planning on using NodeMCU and Lua for
endpoints. But I got bogged down learning yet another framework for
configuration and development.

I cannot overstate the utility of using standard Linux infrastrature for
embedded development. Releveraging systemd for boot/cron type configs and
scripting in Python really cuts into the development time, even for simple
projects.

My next frontier are TFT LCDs. With an ILI9341 fb driver, it's pretty
trivial to connect 2.5 inch displays to SPI to run X for a local display.
And at an $8 price point shipped, they are almost as cheap as the 16x2 LCDs
from long ago. Here is a sample page describing their usage with RPis:

http://raspberrypi4u.blogspot.com/2014/12/raspberry-pi-connect-tft-lcd-with.html

Getting back to the original project, garden irragation, you can definitely
leverage all this technology to do it. Standard drip irrigation systems use
24VAC for control signalling. RainBird has a $30 drip irrigation starter
box that has everything you need to connect and direct a drip irrigation
system to the house water supply. Switchable water valves run the $13 range
and as I pointed out before are easily switched using either a TRIAC or a
relay.

I've gotten my container plant drip system up to manual control. Automatic
switching is still a bit off because the available hose bib is sweated on
and leaks when turned on. So I have to get that figured out before I can
leave the valve open 24/7.

I'm snipping the rest of the post.

-- 
Byron A. Jeff
Associate Professor: Department of Computer Science and Information Technology
College of Information and Mathematical Sciences
Clayton State University
http://faculty.clayton.edu/bjeff