Radio or laser link?. A transmitter intended for radio controlled models would work if fitted with a directional aerial. If you have line of sight then an optical link using a modulated laser pointer is theoretically possible but 400m is a long shot.
I think that aiming will be the hardest part with a Laser. You could get that sort of range with a modulated light bulb. Here's what you do for either laser of lightbulb:
At the transmitter end you make an open ended box, lets say 10CM on a side. The insides of the box are painted with the flattest black paint you can get. The light is placed at the center of this box. This makes an easy target to line the receiver up on.
The transmitter pulses the Laser at, lets say 500Hz. It uses a crystal oscillator for timing.
At the receiver, you use a telescope to make the image of the inside of the box fall onto a photo detector.
The receiver electronics has an amplifier and lets say the dreaded PIC or an 8051 with ADC. The amplifier contains a modest band pass filter. The micro runs on a crystal so that its timing is very good. Creating a bandwidth less than 1Hz isn't hard to do in a micro.
How large is the holding tank? If it is able to contain sufficient water for several days of use then you only need to top it up once a day.
A system I used in our previous house (in the Scottish Highlands) was to install a ball valve in the receiving tank and a pressure switch in the pump drive pipe. When the pressure at the pump rose above a preset level the pump turned off. It stayed off until the next day. I used a timer but, since your pump is solar powered, you could use a relay to hold the pump off. The relay will drop out when it gets dark and the pump will start again the next day.
There's only one caveat. You may get a pressure surge when the pump starts and you'll need to use a timer to ignore that.
snipped-for-privacy@cwnet.com wrote in news:1178518058.279436.319380 @e51g2000hsg.googlegroups.com:
A ballcock on the tank and a pressure switch at the pump is what I'd do.
Going all Rube Goldebergish, I'd have the emitter and receiver at the pump end, and use purely optics at the tank to reflect the laser back or not, depending on the level in the tank.
I can get power at the 15000 gallon concrete tank and favor a tip switch firing up a laser aimed at an isolated target pickup at the pump, but have trouble with picking the receiving component . Thanks to all who have responded so far.
The open tank is about 160 feet of lift as well the considerable horizontal distance, so when the 7 foot tall by 20 foot diameter tank is at bottom the pressure is +-80pounds with full tank only
+-3.5pounds higher. It is difficult for equipment to discriminate this small difference. Secondly, there are at least 8 elbows in the pipe making it difficult to snake a wire, but that,s a neat thought.
Find, or get someone to design, a float valve like a toilet flusher float valve. When the water rises to a certain level, it positively stops the flow (a la your toilet tank).
Your pressure sensor (at the pump end) would be set to cut off at +85 or
+90 PSI, so the pipe would be pressurized. As you use the water, the float valve opens, the pressure in the pipe decreases, and you start your pump.
Looking up pressure switches is left as an exercise for the reader. ;-)
At 1200 feet, you could spot a laser pointer with a spotting scope.
Put a photodector at the focal point of the spotting scope (the "real" image"). Modulate your laser pointer, and demodulate the photodetector signal at the receiving end.
You can get the Laser part of a Laser pointer without the casing. If you add a really good heatsink and pulse the current in 1uS blasts, you can run them well above the makers intended current rating.
You can buy:
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If you apply a current pulse that is short enough, you can bang this with 100mA and it will survive.
Rich, This solution is easily within my ability set and clearly the most sensible way to do the job. However, I'm mostly retired and have the time and basic soldering and electronic tools to go for some form of the laser thing.
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