My solution to the SMT oven controller can be found at; http://www.iis.com.br/~alexg/oven.pdf Enjoy, Peter Homann mailto:Peter.Homann@adacel.com Adacel Technologies Limited, 250 Bay St, BRIGHTON, 3186, AUSTRALIA http://www.adacel.com Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960 Mobile 0421-601 665 -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of David Harris Sent: Monday, 2 December 2002 11:31 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [OT]: Toaster oven thermostats (SMD cooking) Hi- Yes, we'd like it -- could be included onto the webpages. David Chris Hunter wrote: > OK - perhaps you're looking at this problem from the wrong end - you'll > probably get thermal inertia problems with type-k thermocouples, so why not > measure the resistance of the heating element? I have a temperature > controlled soldering iron design that uses this principle - all it needs is > a triac to turn the heating element on and off, a comparator IC, a > transistor, and a few passive components. Temperature is set with a linear > pot. Calibration requires the use of a type-k, but once it's set up, it > will maintain the temperature you've set +/- 2 C, and only takes about 20 > seconds to get there. A check of the tip temperature at various settings > showed that once calibrated, it was pretty good.... > > If anyone wants a sketch of the circuit, you can e-mail me off-list. It > might take a day or so to locate the original design (it's buried in a > filing cabinet), but some of you may find it useful.... > > Chris > > ----- Original Message ----- > From: "Roman Black" > To: > Sent: Sunday, December 01, 2002 11:49 AM > Subject: Re: [TLUG]: [OT]: Toaster oven thermostats (SMD cooking) > > > Wagner Lipnharski wrote: > > > > > I just ordered an electronic thermometer with a type K thermocouple to > > > build the temperature control for my oven. > > > > > > Setting the thermostat for 200F, it seems that the temperature goes this > > > way into the oven; > > > > > > 500F .-'-.OFF OFF > > > .' | '-. -'-. > > > / | '-. .' | '-. > > > 200F---------/----|---------'-.------------/---|-----'-. > > > / | '-. / | > > > 150F .' | '-. / | > > > 130F .' | '-.' | > > > .-' | ON | > > > 80F-'ON----70s--->|<--------9min------->|-30s--| > > > > > > > > Hi Wagner, that is a great post, especially the text based > > charts! :o) > > > > Interesting the use of 1N4148 diodes as temp sensors. > > Quite cheap and seems to work well. But are you sure > > this will be a reliable long term solution? Normally > > SMD soldering charts etc show that silicon deteriorates > > badly if kept at an excess of 200'C. The diodes might > > not last very long... > > > > One more point, your oven has a HUGE thermal lag!! > > This is why you are getting the long cycling times. > > As a comparison, my little toaster oven which is about > > 40cm wide and 25cm high, cycles for 2 seconds ON and > > 3 seconds OFF when regulating at around 150'C. > > The total thermal ripple is only a few percent. > > > > When choosing a toaster oven, find one with large > > power (1500W minimum) in a TINY box if possible, with > > elements above and below the cavity, pref exposed. > > The right oven will regulate at temp with no mods > > needed. If you need to go to production quantities > > then a proper controller will be a great help, but > > if your oven is thermally unsuitable then maybe you > > should be looking for a better toaster oven?? > > > > Also, you can buy good quality mechanical thermostats > > with external copper sense bladder (about $25), if > > you couple the sense bladder to the element they > > will regulate very closely, within a couple of degrees. > > Most of the problem with mechanical thermostats is that > > they are cheap garbage or just located too far away > > from the heat source. > > -Roman > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- David Harris OmniPort Home Page: http://www3.telus.net/OmniPort1/ Discussion egroup: http://groups.yahoo.com/group/OmniPort Swiki: http://omniport.swiki.net/1 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body