If you'll live here in the Romania (East Europe) I'll suggest you to
buy an one week programming timer (about $12). But nothing is much
funny than doing everything with your own hand, so:

Very fast advices:

1. for a real time clock you don't need any auxiliary components
except a PIC and a precise quartz or oscillator.


For software take a look here:
 http://www.geocities.com/vsurducan/electro/PIC/two.html#clock
and check also the link here:
http://www.ezy.net.au/~fastvid/one_sec.htm


Once you have solved your flow algorithm, driving the solenoid is not
too complicated, use an output pin of your PIC, one limiting resistor
to the transistor base (about 1k to 3k3) of a npn transistor. In the
colector of the transistor connect one pin of your solenoid, the other
solenoid pin connect it at +12V. transistor's emiter must be connected
on the ground (the -5V point) One diode must be mounted with the anode
(the terminal is marked with a white line) to the +12v and the catode
on the other pin of the solenoid, directly on the solenoid pins.
(1N4001 for example).

Check first with an ammeter (connected in series with the solenoid)
how much current it drawns the solenoid connected directly to the 12V
supply. Based on that value, choose the NPN transistor with a
collector current at least twice the one measured and a
colector-emiter voltage of four times bigger  than the supply value.

That should be all,
success,
Vasile


On 7/30/06, Hop <hop@cableaz.com> wrote:
>
> I have a little experience with PIC microcontrollers, and the programming
> part of my project is something I should be able to handle.
>
> What I need help with is the external aspect of my project, specifically,
> interfacing my PIC board to my Orbit sprinkler valve.
>
> All I want to do is turn on my Orbit valve (12v I think, via solenoid) at
> 10am and off at 7pm. This valve feeds my misting system, that keeps my dogs
> cool during the hot Arizona summer day. I tried using my 9 zone timer to
> control the valve, but I only get 99 minutes max per zone, per daily event,
> and if I try to daisy chain the events to get a long duration on the misting
> system, all the other zones fire too, which makes using the timer
> impractical.
>
> So I have this valve that works just fine. I just need to turn it on, leave
> it running for 10 hours or so, and then turn it off, daily.
>
> I figure that a PIC microcontroller is perfect for this application. I can
> use a Maxim DSI 7887-3 real time clock module to make sure it fires close
> (within a few seconds a month) to the time I need it to fire. I just don't
> know how to go from there. I would like to use something solid-state to
> control the 12v to the valve, but have no idea how to design the circuit, or
> how to limit the current, or what the solenoid needs. A pulse? A constant
> voltage?
>
> I know I'm asking a lot of nooby questions here, but all I've done with the
> PIC is talk to my PC via USB, and control LEDs. I know. Sad. =O
>
> Any thoughts and/or help I can get with this outdoor project would be
> greatly appreciated! I kind of want to do-it-myself anyway. I could put my
> electronics bench to work finally, after dusting, and it would be nice if
> one of my PIC creations actually did some work around my house... FINALLY!
>
> Hop
> --
> View this message in context: http://www.nabble.com/Homemade-Misting-System-On-Off-timer-tf2021545.html#a5558365
> Sent from the MicroControllers - PIC forum at Nabble.com.
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist