KMoffett

http://www.picaxeforum.co.uk/showthread.php?t=12266 Something I did a while ago. I would put the uC circuit at the roof tank, and run the control line to the pump "down" to the pump switch circuit. Mine was a continuous sense program, but if you only need to sense periodically, once a minute?...hour?...day?... that would work too. Ken

A problem with that design is that you are passing a DC current through the common and lo electrodes most of the time. This will causes electrolysis that will corrode the electrodes. Designs that have constant submersion of electrodes need AC drive/sensing to minimize this. Ken

ECG/BP simulator with programmable outputs for various rates and abnormalities. Ken

Windshield washer pumps won't work. They have plastic motor bearings. They're meant to run for only a second or two at a time. If you try to run them for much more than that the bearings will melt. I tried several different ones. Been there...done that...smelled the burnt nylon. :( Ken

Why 12V battery to inverter to 240VAC pump? The inverter stage will waste power. Just use a 12V water pump directly from the battery. http://www.faludi.com/2006/11/02/moisture-sensor-circuit/ 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. Ken

You need to add hysteresis feedback. This will require a higher voltage than 10.55 (you select) to switch the light back. http://www.intusoft.com/onsemipdfs/LM324-D.pdf Look at Figure 13 for the circuit and formulas. Ken

Google: 4017 traffic light Ken

Or, two LEDs in series with one resistor. (5v-1.7V-1.7)/0.01A = ~160ohms I use ExpressPCB's free schematic capture program. http://www.expresspcb.com/ There are others like Eagle and PCB123, but I just like the ease and versatility of this one. Ken

The relay is SPDT (single-pole/double-throw) so it's just a matter of using the common and normally-closed contacts, rather than the common and normally-open contacts. :) Ken

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. http://www.arcade-electronics.com/detail.aspx?ID=17763 Ken

Jake, You want to run pairs of LEDs off of 115VAC...or just the timer? Ken

Google: Blinking Halloween Eyes Ken :)

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. Ken

Or: 4. Microcontroller>Darlington>Valve 5. Microcontroller>MOSFET>Valve If you don't need to isolate the valve's power supply's ground form the microcontroller's power supply ground, then #3, #4. or #5 will be the cheapest and easiest. #3 and #4 will require a base resistor, #5 won't. Ken

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? ???? :) Ken

Google: candle flicker led circuit There are a lot to choose from. Ken

Do you have a make/model and link to the datasheet? Are you thinking of trying to use an On/Off solenoid valve in a proportioning mode? Ken

I just knew there would be a market for all those magnetron magnets I've pulled from dead microwave ovens. Lets see, (2 per magnetron x $4.50) + $20 excessive shipping charge...that's $29 per dead oven. ;) ken

Not a lot of info! Looks like PD2 and PD5 should have pull-up resistors. Floating inputs can cause all kinds of program problems. That would be my first guess. Ken

Good writing skills for starters. ;) ken

Probably it will work. 12A rated contacts carrying 14A will likely not make much a difference if the 12A relay is a good quality one. Do you know if the circuit you will be switching with the relay actually draws 14A? Ken