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Posts posted by KMoffett

  1. Why 12V battery to inverter to 240VAC pump? The inverter stage will waste power.  Just use a 12V water pump directly from the battery.

    Since your sensor probes will always be in moist soil, this circuit will cause the electrodes to corrode over time due to electrolysis from the DC current between them.  A better circuit would one one that uses AC for the detection circuit. Like:http://www.electronicsforu.com/efylinux/circuit/cir80.gif. Also use stainless steel rod or wire for the probes...as copper is toxic to plants.


  2. LEDs, even the ones from a 115VAC strings, are 1.7VDC to 3.4VDC, depending on color.  So you will need a low voltage power supply anyway.  Here is a timer that could work.  The long period is 2.5 to 60 seconds and short pulse is 0.5 to 5 seconds.  These can be changed to your time range by replacing several components.  You would need one timer for each pair of eyes.  The output is a relay that could be used to switch low voltage DC or 115VAC lights.


  3. Isolating the the digital power ground from the load power ground, is as you say, to keep the large load currents from traveling through digital ground traces. These currents can cause voltage drops along traces that the digital circuits misinterpret as signals.  If you arr not using isolation interfaces, opto-isolators or relays, you want to connect the load ground to the control ground a one, and only one, point.

    Also when interfacing low voltage DC control circuits with AC line devices isolation helps protect the control circuit from the high voltages and voltage differences between control grounds and AC Neutral ground.


  4. The linked data sheet said the power draw is 6VA (6 watts).  But, I would go with what is marked on the the valve, 3watts.

    Yes, by proportioning I meant PWM driven to achieve a variable flow.  Some people want to do this with ordinary valves...and it doesn't work.

    The coil current on your valve will be 3w/12V = 0.25A.  Almost any small relay with contacts rated at 1A DC should work.  I don't think that "optoisolators" are usually rated for that high a current.  I think you would be looking for "DC solid state relays".

    To back up a bit...what are you trying to do in this project?  What are you using to control the relay that controls the valve?.  Do you need isolation between the valve and the controlling device? ???? :)


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