100 days a year off; you must be a school teacher! ----- Original Message ----- From: "Chris Carr" To: Sent: Saturday, August 18, 2001 4:32 PM Subject: Re: [EE]: Isolated I2C > > >Give me a couple of hours and I will post a circuit. I have to do a > couple > > >of urgent jobs first. > > > > Appreciate that. It is not urgent (I will not be looking at it till Monday > > anyway), so do not bust a gut over it. > > > You mean you are not working 12+ hours a day, 265 days a year. I must be > doing something wrong, it cannot be just age related. > > The scanner has decided to throw a wobbly and the Digital Camera is in > Scotland being "evaluated" by one of my Nephews, so I will attempt to > describe the circuit. > > Two Identical circuits are require for SDA and SCK. I will describe SDA. > > Each Circuit requires > 2 off BAT85 or similar (OA47 ?) low volts drop is important, call them D1 > and D2. > 2 0ff 6N139 optocoupler with Darlington Output. Call them OC1 and OC2 > > Assume we have two Isolated Circuits called Left Hand (LH) and Right Hand > (RH) > > The Collector of the first transistor of OC1 (Pin 8) is connected to RH > +5volt > OC2 Pin 8 is connected to LH +5v > > The Emitter of OC1 (Pin 5) is connected to RH 0v (Earth) > OC2 Pin 5 is connected to LH 0v > > The Collector of the Second Transistor of OC1 (pin 6) is connected to a 3k9 > resistor, the other side of which is connected to RH +5volt > OC2 pin6 is connected to a 3k9 resistor the other lead of which is connected > to LH 5v. > > The Cathode of D1 is connected to the Anode of the Photodiode of OC1 (pin 2) > D2 Cathode is connected to OC2 pin 2 > > The Anode of D1 is connected to the Cathode of the Photodiode of OC1 (pin 3) > The Anode of D2 is connected to OC2 pin 3 > > The Anode of D1 is connected to LH SDA > The Anode of D2 is connected to RH SDA > > The Cathode of D1 is connected to OC2 Second Collector (pin 6) > The Cathode of D2 is connected to OC1 pin 6 > > The assumption is made that the mandatory 3k3 pull-up resistor is present on > both LH and RH SDA Lines. > > Circuit Operation. A low on LH SDA causes LED OC1 to light (path through the > 3k9 resistor). This results in the second transistor of the OC1 Darlington > Pair to turn on taking the RH SDA low through D2 (current through the 3k3 > pull-up resistor). > > If my description is inadequate Alan, Email me off-list with your Fax number > and I'll send you a copy of my sketch which is currently on the back of the > Marlborough Pack. 8-) > > Regards > > Chris Carr > > -- > 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