"Have you had these suicidal impulses for long? :-)" It was much stronger in my last life. :-) I SHOULD CLARIFY ONE THING ... the level-detection and temp sensing occurs only during filling. Once it's filled, it will be shut off. That said, I am aware of the issues of 110VAC in a tub, which I why I wanted to use just a few DC volts. I'm not aware of the leakage etc with relays. Are you suggesting that there's potential danger with 4.5V DC in a tub? Or are you saying that the 110VAC from one of the relays could leak to the 4.5V side of the circuit? No existing temp sensor -- just switch on both valves and dump hot and cold water for a specific time. Variances in water pressure, and hot and cold temp make that incredibly inconsistent. Sometimes it works out, and sometimes I need to add hot water to get the temp right. Thanks, -Neil. ----- Original Message ----- From: "Reginald Neale" To: Sent: Thursday, March 28, 2002 3:29 AM Subject: Re: [PIC]: Automated whirlpool tub ... > Neil: > > Have you had these suicidal impulses for long? :-) > > I'm sure you are aware of the huge safety issues. Isolating all > your line voltage switching circuitry from the control circuitry > is not trivial. Relays are good, but there's creepage, leakage, > physical barriers... > > Even for the level sensing, it's probably not a good idea to get > your voltages wet. Aside from the safety issues, output from electrodes > in contact with the water/chemical solution may not be stable. > For level sensing, GEMS makes some float-type modules that are very > reliable and inherently isolated. > > What does the existing control system use for temperature sensing? > You can probably adapt that same sensor to your new circuit. > > Reg Neale > > -- > 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