Updated 2014.07.20

List of newly found excellent references

 

Tip122 from Arduino

Good quick reference (has all parts) of NPN PN2222A transistor

 

Update 2014.07.19 10.26 - Grrr

Grrr so - micro controllers a pretty whimpy for sourcing or sinking current. Regrettably, so is the PCF8574 io expander.  And more Grrr !     the 8 X Relay module are controlled by opto-isolators.  Ok, that "might" be good .. But .. and here is the double Grrr ! part - the modules come with another LED for a visual indicator (in addition to the opto-isolator) ..   So it adds up to be 50+ ma per input which needs to be sunk .. and the gutless PCF8474 can only sink 20ma :( 

I thought about desodering, or grinding off the LEDs .. but the PCF8574 is still probably too weak to sink the necessary current for the opto-isolator ..  Meh .. so I've got to add MORE COMPONENTS :(

8 x 2N2222 and 8 1K resistors

wired like this except up to a PCF8574 instead of an Arduino Uno

Update 2014.07.19

Raspi & I2C module both appear to be working. Yay !

Now it's time to install MRL - dropped the myrobotlab.jar - ran 

java -jar myrobotlab.jar -update

it didn't work - but the prelog does :P

Here the raspi is downloading all the services

This is one of my current top 4 things to finish on the Borg Todo List.

MRL will be controlling my sprinklers (it has for years - but since the electric valves were outside, winter destroyed them).  Since I need to replace the valves, it seemed like a good time to upgrade the hardware too.

Previously I used an Arduino controlling my own TIP120 transistor switches.  

I found some big 5VDC coil relays on the internet for very cheap.

 
But they drove me NUTS ! ..  Had to comb the internet for any documentation at all..  Finally a schematic which showed it supported electrical isolation with a phototransistor.  Ok, I hooked it up, but did not care about the isolation but it always behaved very strangly ... sometime it worky .. sometime no.

Now Boss#1 (wife) came home from Japan trip and found no automated sprinklers.  Oops.. ok so I had a closer look at the schematic and the printed board and realized that it HAS 2 GROUNDS !!!! even if you do jump together both sides of the 5VCC & JDVCC.  After tying the grounds together it works solid.

Quick trip to the Home Despot .. and I put together the Uber Manifold for the sprinkler systems.

I'm putting this together from re-cycled parts - so I happened to have a super-beefy 5VDC regulator which should be plenty power for the raspi, I2C digital io board, & the 5V side of the relay module.  Did not have the right molex connector, but nothing a quick solder can't fix.  

The whole thing will be fed by a salvaged 21 VDC power supply.  The valves are supposed to be 24V but I've seen them switch as low as 12V, so I think I'm good there.

Next will be to clip a micro usb connector and hook it up to the regulator - will be the power for raspi coming off the regulator.

 

PCF8574 - I2C Module $6 -