Post by thread:[EE]: Isolated I2C

I've played only with isolated 232 and other isolation devices in medical equipment. However for clk I think will work any photodiode-phototransistor optocoupler like CNY17 or 4N series, depends on max frequency requirements. For data, I'll use two high frequency trigger schmitd inverter like MOC 5007 or H11L series, both have a two input nand gate which could be use for enabling the sense of transmision ( receiving or transmiting ) and run well up to 100kHz. Vasile On Fri, 17 Aug 2001, Alan B. Pearce wrote: {Quote hidden}> I have a requirement to have an I2C link across an isolation boundary. The > voltage requirements of the boundary are not high, it is just that I am > needing to emulate some circuitry for testing purposes from the rest of the > test equipment. > > I will not need to be running the I2C link at high speed, so I was thinking > in terms of opto-isolators to achieve this. Anyone have any experience in > this area, especially the bi-directional part? > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I did this a short while back. The device under test is powered by a dropping capacitor, so isolation was required for the interface. It's not quite the I2C protocol, but modified to reduce code size. It's a PIC12CE518. The I2C on the measurement side (an 8051) ended up using three pins (clock, tx, rx). The PIC device under test uses two pins with pullup resistors. Same principle as I2C, though. I used three (3) 4N36 with the base grounded through a resistor to increase turn-off times of the phototransistor. The base resistor is a compromise between speed and current. So you might play with that for your circuit. One for the clock, one for tx, one for rx. I also ended up using a small NPN to interface to the circuit under test, which has very low drive capability. The whole thing is powered by an audio transformer driven like a half-bridge converter to provide the power for the optos. No feedback to keep it simple. Since the PIC is powered by an Xcap, it really has very limited drive, so this was necessary. I can take a quick rise/fall time measurement of my configuration if you are interested. Feel free to ask for more details. > {Original Message removed}

No problem. We use OptoIsolators. Do you want just the Clock and Data Lines or Clock, Data and Interrupt. ? Regards Chris Carr > I have a requirement to have an I2C link across an isolation boundary. The > voltage requirements of the boundary are not high, it is just that I am > needing to emulate some circuitry for testing purposes from the rest of the > test equipment. > > I will not need to be running the I2C link at high speed, so I was thinking > in terms of opto-isolators to achieve this. Anyone have any experience in > this area, especially the bi-directional part? > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> >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 spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

100 days a year off; you must be a school teacher! ----- Original Message ----- From: "Chris Carr" <.....nyedKILLspam@spam@BTINTERNET.COM> To: <PICLISTKILLspamMITVMA.MIT.EDU> 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 {Quote hidden}> > 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 {Quote hidden}> Marlborough Pack. 8-) > > Regards > > Chris Carr > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Mick Kent wrote : > 100 days a year off; you must be a school teacher! Finger problems, It should have read 12+ hours 365 days a year. I live in hope of being able to afford one day off every 4 years 8-) Chris Carr {Quote hidden}> > > > > >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. > > -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

>Mick Kent wrote : >> 100 days a year off; you must be a school teacher! >Finger problems, It should have read 12+ hours 365 days a year. >I live in hope of being able to afford one day off every 4 years 8-) >>> 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. I don't get paid enough to do that - I'm only a lowly civil servant who is worse off than the nurses, police firemen...... etc. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads