When you say "monitor speed" just what do you want to know? All I can think of is too fast, too slow, stopped or "erratic". Each condition needs a definition. John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 johnferrell@earthlink.net Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" ----- Original Message ----- From: "Patrick B. Murphy" To: Sent: Tuesday, September 02, 2003 2:59 PM Subject: [PIC:] How to monitor a dozen shafts? > Hi all, > > I am a hobbyist who is trying to help a friend with a project. He > wants to monitor the speed of about a dozen shafts on his potato > digger. The shafts normally run around 200 rpm, but each shaft may > run at a different rpm. One or more shafts may even stop if the > digger is overloaded. I am wondering which approach you might > consider most feasible to monitor so many shafts. On each shaft is a > 16 tooth sprocket and a hall effect sensor. I already have a 5.7" > LCD display from Amulet Technologies to display the speeds. > > One idea I have is to use one PIC16F877 and a 16 to 1 multiplexer > (or two 8 to 1 multiplexers if a 16 to 1 doesn't exist) and measure > the pulse period of each shaft in turn. The trouble with this is if > a shaft is turning at, say, 30 rpm, it may take a long time to get a > reading. If I am correct, with a 4MHz clock and Capture Mode set to > every fourth rising edge, it would take a half second; 15 rpm would > take a full second. If more than one shaft is turning so slowly, I > think the time it would take to update all the shaft speeds would be > unacceptably long. If I set Capture Mode to occur on every rising > edge instead, this situation improves but I'm guessing my RPM's may > show a lot of fluctuation as the input frequency may not be stable. > > Another idea is to dedicate a PIC that has a UART to each shaft and > poll each of them in turn. Those PIC's could either measure the > pulse periods or count the pulses. I have some PIC16F628's available > to try. > > Any other ideas or advice? I've enjoyed reading the posts for a few > years now, and finally am finding the time to try a few projects. > > Thanks in advance, > Patrick Murphy > James Valley Colony > > P.S. I have put together an Excel spreadsheet showing Hertz to RPM > and pulse periods using the various Capture Modes and a 4MHz (or > other) clock. If anyone is interested in it, let me know off list > and I would be glad to e-mail a copy to you. > > -- > 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