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Oh, if they need to go both directions, the L298D is just what you want - I didn't realize there were zone valves that worked like that.
I've never heard anyone complaining about the time it takes to get data from the DS18B20, though the module code does not let you provide a callback (ie, getTemp() will block until it returns). I may be missing something, as I haven't worked with oneWire bus before.
In modules that expect to take a while waiting on some device, often they'll take a callback function as an argument when you call it, do stuff in the background with intervals/timeouts, and then call the supplied function, with the results as arguments, when done.
DrAzzy-
The reason my DS18B20's appeared slow is because I had them wired for parasitic power (ie power derived from the data line, no separate V+)
I tried powering them directly and they returned the temperature very quickly so I should have no issues with blocking!
I had no idea that the power mode has such an impact on response time.
DaveNI
Thanks for all the great responses!
I will definitely investigate the web server approach.
The main reason I was thinking about using the L298d is that the zone valves are reversible - to open & close. If using relays I need 4 of them for 2 valves - I thought the l298d may be more economical!
Just one question - the ds18b20's can take 750ms to take a reading - will I need to wait for the response or does the event based approach allow me to do other things while waiting?