You only really need a 6 pin device with an on board clock and you get 2 spare pins for programming or perish the expense a couple of led's Steve -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Phil Keller Sent: 14 July 2013 21:07 To: Microcontroller discussion list - Public. Subject: Re: [EE] Looking for a more eligant solution Maybe a better description would be that the desire is to: - Enable an exhaust fan if the internal temperature is greater than the external temperature by about 5 degrees && if the external temperature is greater than about 70 degrees. The fuzzy numbers are there because there is no real need for high accuracy. This is an exhaust fan and if it is off by a couple of=20 degrees that is OK. The use of hysteresis is to prevent hunting or=20 oscillation if the temp difference is 5 degrees or the outside temperature is 70 degrees. An Arduino is overkill. What I was fishing for was an elegant=20 minimalist solution. A PIC12F67, or such, is a couple of bucks and the remaining circuitry is another $15 so for less than $20 it could be "done" but I just keep thinking that there has to be a better solution. -Phil- PS Presently I am leaning towards the PIC/1-wire with a 5v relay/FET solution. As you mention lots of flexibility and easy to do. -------------------------------- Long ago when men cursed and beat the ground with sticks, it was called witchcraft.. Today, it's called golf. On 7/14/2013 12:43 PM, Denny Esterline wrote: > This is one of those "best" questions which really don't have a "right" > answer. > As I read your spec... > Outside temp > 70 F AND (Inside temp + 5 F) > Outside temp THEN FanOn=20 > There are several purely analog mechanisms that come to mind. > > Problem is, your spec isn't that clear. :-) the "~70" and=20 > "probably...hysteresis" leave this vague enough that I wouldn't want=20 > to do something that doesn't have quite a bit of flexibility. That=20 > could be pots and jumpers on an analog board, but personally, given=20 > this spec, I'd lean strongly in favor of the small PIC solution. I'd=20 > also steer away from thermistors. Given the one-off nature of the=20 > project, digital temperature sensors will save you _much_ more time=20 > than the couple extra dollars they cost. Make it much easier to remote mount the sensors as well. > > Frankly, this sounds like a perfect project for an Arduino. I believe=20 > you can get all the necessary building blocks off-the-shelf. > > -Denny > > > > On Sun, Jul 14, 2013 at 7:52 AM, Phil Keller wrote: > >> A friend of mine was wondering if I could build a simple device for=20 >> him. He is looking for something that senses the outside and inside=20 >> air temperatures. If the outside temperature is greater than ~70 and=20 >> if the inside temperature is 5 degrees greater than the outside=20 >> temperature it would enable an exhaust fan. (We would probably need=20 >> some hysteresis on the temperatures to keep the fan from oscillating=20 >> ON-OFF.) >> >> I can see how this could be done easily with a small PIC, a couple of=20 >> thermistors, a FET & relay and a 5v power supply. >> I could also do it with a few comparators, logic gates, FET & Relay,=20 >> thermistors and a power supply. >> >> Both of these solutions seem overly complex for the problem. Does=20 >> anyone have a more simplistically elegant solution? >> >> Thanks >> -Phil- >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 >> View/change your membership options at=20 >> http://mailman.mit.edu/mailman/listinfo/piclist >> -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .