I would be interested in this circuit and code if you don't mind. You = can email me separately at=20 glb@djgrp.com Thanks -----Original Message----- From: Larry Bradley [mailto:lhbradley@IGS.NET] Sent: Tuesday, April 22, 2003 10:45 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]: Simplest high/low water pump control Hi John. What is the fluid? If it is water, I've built a circuit for the bilge pump in my sailboat. = I only have one level to worry about, but it is easy to use more than one. I use two small stainless steel bolts as sensors, about 1 inch apart on = a piece of Plexiglass.. One of the things you have to avoid is having DC going through the electrodes - this can result in corrosion. The way I handle this in my PIC-based controller is to alternate the drive to the bolts. On one measurement cycle, one pin is driven and the other is = ground, and on the next cycle I reverse this. The result is there is and AC = current through the bolts, not DC, so there is no corrosion. I've sent you the schematic in a separate post. The program, unfortunately, is written in PicBasic Pro (I can send you a copy if you want - it will show you how things work). The program tests for current through the probes, and if there has been current for 15 seconds, the pump motor is turned on. It is turned off = when the current through the probes has stopped for 15 seconds. This is how I solved the "sloshing around in the bilge" problem. It also has an option to monitor pump motor current (using the 0.15 ohm resistor and the 682's comparator). I turn on the pump for 100 msec once every 15 minutes and use the comparator to check the current. If the current is less than an amp, let's say, then I know the pump is pumping air, so I turn it off. If it is drawing more than 5 amps, I know the = pump is stalled, so I turn it off. If between 1 and 5 amps, the pump is = pumping water, so I leave it running until the current drops down again. This = is just a belt-and-suspenders thing, in case the probes get grundged up = with stuff. If you want to sense two levels, you could use two sets of probes, one = for high level and one for low. Depending on how far apart the levels are, = you might just need three bolts - high, common, and low. How well things work will depend to some extent on the water you are sensing. I've used my system with local city water, water from the = Ottawa River, where I used to keep my boat, and water from Lake Ontario, where = I keep it now. All works well with the setup shown. Larry At 10:20 AM 4/22/2003 +1000, you wrote: >I need to keep the fluid level in a tank in a particular range. I have = a >little 12v pump to do the job, but now just need the simplest possible >circuit to turn the pump on when the fluid is at the "low" mark, and to >switch it back off fluid is at the "high" mark. I intent to just use >stainless steel or copper rods as the water level probes. > >What is the easiest/cheapest way of doing this? > >John > > > > > >_______________________________________________________________________ >John Brown >PhD (Clinical Psychology) candidate > Email: john.brown@anu.edu.au >School of Psychology Phone: (02) 6125-3827 >Room 124, Building 39, Psychology Fax: (02) 6125-0499 >The Australian National University Mobile: 0429 455 504 >ACTON ACT 0200 Web: http://www.anu.edu.au/psychology/staff/BrownJ.htm > >-- >http://www.piclist.com hint: To leave the PICList >mailto:piclist-unsubscribe-request@mitvma.mit.edu Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads