Post by thread:[PICLIST] [EE][PIC] Long distance I2C

I'm trying to run a remote I2C temp sensor over phone cable 50m away into a PIC. It needs to be very reliable and cheap. My first assumptions are: Run slow out of the PIC since I can control the bit rate and therefore reduce effect of slew due to cable capacitance. Second, use a driver of some sort out at the I2C sensor to isolate the I2C sensor chip from cable capacitance/impedance and protect from induced transients. Has anyone done this and know all the "gotcha's"? Easiest way of implementing a driver/receiver circuit? Transient protection? etc.... thanks, Jason Wolfson ___________________________________________ Lipidex Corp 50 Franklin Terrace Duxbury MA 02332 781-834-1600 781-834-1601 FAX spam_OUTjasonTakeThisOuTlipidex.com ____________________________________________ -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

----- Original Message ----- From: "Jason Wolfson" <jasonKILLspamLIPIDEX.COM> To: <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Sent: Tuesday, October 03, 2000 4:51 PM Subject: [EE][PIC] Long distance I2C {Quote hidden}> I'm trying to run a remote I2C temp sensor over phone > cable 50m away into a PIC. It needs to be very reliable and cheap. > > My first assumptions are: Run slow out of the PIC since I can > control the bit rate and therefore reduce effect of slew due to cable > capacitance. > > Second, use a driver of some sort out at the I2C sensor to isolate > the I2C sensor chip from cable capacitance/impedance and protect from > induced transients. > > Has anyone done this and know all the "gotcha's"? > Easiest way of implementing a driver/receiver circuit? > Transient protection? etc.... You might like to look at the Philips I2C extender chip P82B715 and http://www.semiconductors.com/acrobat/applicationnotes/AN444.pdf "Using the P82B715 I 2 C extender on long cables" From the summary: The P82B715 I 2 C Buffer was designed to extend the range of the local I 2 C bus out to 50 Meters. This application note describes the results of testing the buffer on several different types of cables to determine the maximum operating distances possible. The results are summarized in a table for easy reference. and www.semiconductors.com/acrobat/applicationnotes/AN452.pdf Application Note AN452 "One Mile Long I2C Communication using the P82B715" LONG DISTANCE I C DESIGN CONSIDERATIONS Summary I 2 C communication is possible over very long distances, but at greatly reduced data rates. Tests were made and results shown for cable lengths exceeding one mile. This report explores the design considerations and trade-off needed to implement a successful long distance I 2 C communication system. Even if you don't use their chip there's quite a bit of useful information there. -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

> I'm trying to run a remote I2C temp sensor over phone > cable 50m away into a PIC. It needs to be very reliable and cheap. > > My first assumptions are: Run slow out of the PIC since I can > control the bit rate and therefore reduce effect of slew due to cable > capacitance. That's a good start, but remember you are dealing with a pretty nasty transmission line, you'll have alot of reflection going on. I run about a 20m length using standard telephone cable. It works OK and is quite reliable. What I have done is I read each device 10 times, drop the lowest and highest result, and average the rest (it is also a temp sensor, the NS LM75 in my case). Before I allow the result I check the range, if it is more than a few degrees I try again. It works and seems very stable although I don't know how many times it has had to retry. Good luck and let us know how it turns out! :) TTYL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use listservspam_OUTmitvma.mit.edu?body=SET%20PICList%20DIGEST