Post by thread:[PIC]: Pet feeder done!

Woo-hoo! I got the last piece of code for the pet-feeder done today (though I know there will be changes and added features). Currently, it uses a 24-hr clock with 5 user-settable feedings per day and variable feed quantities on each feeding. Uses 3 buttons -- mode, up and down. HW is 1 pic 16F872, 4 7-seg digits, and some glue (3 driver transistors, some resistors, a crystal, etc). I've setup a timing test where I'm running the code simultaneously with a trusty stopwatch. Is there some accuracy threshold that I should be looking for? By that, I mean what is considered poor timing accuracy... how many seconds per day, or hopefully, per month. Also playing with the feed settings/alarms while that test is running. Next up .... the mechanicals, which is also being worked on by a friend. Thanks, -Neil. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

In such an application I wouldn't be to worried about timing accuracy. Think is your dog going to notice if he is fed 1 minute earlier each day? Think what would happen if you ate supper exactly one minute earlier each day then the day before, you would never notice. (and this is extremely low accuracy for a pic you should be able to get <1 sec no trouble). Now if it's commercial idea I'd make it accurate to less then a sec or so, if it's for yourself, I guess that's for you to decide (depends on your personal degree of perfectionism :) Just my two cents. Hope it helps, Aaron -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

You're right -- I'm not too worried about accuracy. A few seconds a day will work just fine, and although we'll build a few for personal use, we've got commercialization in mind (later). Only real reason for the test, is that this is my first PIC code which requires "accurate" timing, so I'd like to know how it works out, and the same project with a 1.8432 Mhz crystal turned out to have pretty poor accuracy (minutes per day). Had something to do with setting TMR0 manually, but I could not find a clear answer to why. Cheers, -Neil. {Original Message removed}

You guys should take a look at the first few minutes of "Back to the Future" (the first one)... If Hollywood can teach us anything maybe it's to have a negative feedback loop with a weight sensor on the bottom of the container... I like it! Adam Smith -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I like to use 32.785 Khz watch crystals for timing things. The added benefit is low power, because of less transistions of the PIC oscillator and associated stuff. The crystals are quite accurate, and the PIC doesn't care how slow it goes. I can't imagine anything that has to happen at >1MHz in a dog feeder. --Lawrence {Original Message removed}

Display multiplexing -- at 32.768Mhz, there is bad flicker. At 131.072kHz there is noticeable flicker, but not too bad -- sort of like a fluorescent bulb, where occasionally you can see the flicker. 1Mhz would cure that for sure. Yes, I've tweaked and tweaked and tweaked to try and reduce the loop time and the display transition time. I'm thinking even 200khz might do the trick though. Cheers, -Neil. -----Original Message----- I like to use 32.785 Khz watch crystals for timing things. The added benefit is low power, because of less transistions of the PIC oscillator and associated stuff. The crystals are quite accurate, and the PIC doesn't care how slow it goes. I can't imagine anything that has to happen at >1MHz in a dog feeder. --Lawrence -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Sorry, I have probably missed something, but how hard would it be to latch the outputs for each 7-seg display with something like HC374's between calls to them? It would increase power consumption, but it sure would make the flicker die. You could refresh at 10 Hz and it would look fine. Brendan Moran {Original Message removed}

BTW, I found a couple possible solutions: - Jameco: 1Mhz 1/2-can ext oscillator @ $1.75 ea - BGMicro: 1Mhz crystal: $0.75 ea - BGMicro: 262.144Mhz crystal: $0.75 ea I'm picking up a few of the BGMicro units to test. Cheers, -Neil. {Original Message removed}

Think I missed this one... Very rough calculation of the extra costs (chip + extra PCB space required) comes to just under $2. For the extra hassles of soldering these, I'd just buy the more expensive crystal, and still be able to mount the end product in a smaller location. Cheers, -Neil. {Original Message removed}

Fair enough. I never said it was the best solution, just one that didn't require multiplexing. ----- Original Message ----- From: "Pic Dude" <spam_OUTpicdudeTakeThisOuTAVN-TECH.COM> To: <.....PICLISTKILLspam@spam@mitvma.mit.edu> Sent: Friday, June 14, 2002 1:00 PM Subject: Re: [PIC]: Pet feeder done! {Quote hidden}> Think I missed this one... > > Very rough calculation of the extra costs (chip + extra > PCB space required) comes to just under $2. For the > extra hassles of soldering these, I'd just buy the more > expensive crystal, and still be able to mount the end > product in a smaller location. > > Cheers, > -Neil. > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

On Thu, 13 Jun 2002, Pic Dude wrote: >Display multiplexing -- at 32.768Mhz, there is bad flicker. At >131.072kHz there is noticeable flicker, but not too bad -- sort of >like a fluorescent bulb, where occasionally you can see the flicker. >1Mhz would cure that for sure. >Yes, I've tweaked and tweaked and tweaked to try and reduce the >loop time and the display transition time. >I'm thinking even 200khz might do the trick though. >Cheers, >-Neil. Then you could use a 455kHz ceramic resonator I think. Peter -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu