page outlines two different kinds of power supply. One is for DC power
(this is to control low-voltage things like the water valve). The other
is for AC power (this is to control standard, houshold voltage and is
more dangerous to work with).
this how-to, we're going to start with the local circuit. The reason is
that this circuit will allow you to control any source voltage (as long
as it's within the rating of the relay and wiring).
The circuit is very simple. It consists mainly of the relay which
controls the source voltage. There is an indicator light (LED and 1k
resistor) so you know if the power is on.
This circuit really needs to be built on a proto-board to make any sense, so there is no example of it on your breadboard.
||Here is a view of
a possible assembly of the components on a 1 inch proto-board.
||Here is a back view. Notice the
screw-terminal -- this is where you will attach the two ends of wire
that you are controlling.
||And this is a top view. Notice
that there is a small piece of paper wedged between the resistor and
the RCA plug -- this was particular to this specific board because the resistor
was too close to the RCA plug and could have caused an electrical short.
||This is the underside of the
proto-board. If you use short pieces of wire as jumpers on the bottom
side like this, you can fit more stuff on a smaller board.
get nice, clean, well-regulated DC power, we will be using an old
computer power supply, also known as an ATX power supply. That little
box that used to power your old pc can deliver a
range of good clean voltages for all sorts of electronic projects. And
most importantly, you
can also combine the +12v and the -12v to get a total of 24v DC --
enough for your Orbit valve or other garden hardware.
Here is a link to an article about How to Convert a Computer ATX Power Supply to a Lab Power Supply
. There are other turoials out there on the web.
is VERY worth while to do this conversion. These old ATX power supplies
serve as reliable bench-top workhorses for years to come.
AC power CAUTION
: The AC power module
makes use of household AC power which is 120 volts in the US (even more
dangerous if your voltage is higher). This voltage can kill you if
handled irresponsibly. Please slow down, take your time, and take
proper precautions. Above all, never
work on electrical wiring while it is plugged in.
(see the parts page)
- small relay
- screw terminal
- RCA jack
- 150ohm (approx.) resistor
- 1 in proto-board
- film canister (or similar small plastic enclosure)
- sturdy, AC rated cable
- male plug end (x2), and female plug end (x1) -- see note
Note: the extra male and the single female plug ends are to make the AC
power unit free-standing. You could combine this module with the
water-valve module if you don't feel like putting on the extra plug
ends for something that will likely stay plugged in all the time
anyway. Personally, I like the free-standing unit.
Please note that this particular build is on kind of a tight scale --
the components are very close together. If you are not comfortable
working this tight, you might consider using a larger proto-board which
also means you will need to select a larger plastic enclosure.
||This is the film canister with
the heavy-duty AC cable run through the bottom of it already (sorry
there are not photos of the assembly of that).
The cable has a crimp connector for the wire that runs straight
through. Then the other wire (the two wires sticking out of the film
canister in the photo) is long enough for you to remove the board for
||Now the wires have been locked
down in the screw-terminals on the board. All we have to do is shove
the board into the canister so that the wires bunch up neatly behind it.
||Once the board is in, you will
want to secure it with a bolt or any solution that won't let the board
move around when you plug the signal wire in -- i.e. the RCA cable.
||This is the finished AC power
module. You can use this inline anywhere you want to control AC power
(up to the rating on the relay) with a 5v signal (such as Arduino).