I didn't realise that you were only trying to send digital data. A 4 - 20 mA current loop seems overkill for that kind of application, as there are much more easily implemented digital protocols. I have used 4 - 20 mA current loops for analogue instrumentation, and made the assumption that you were trying to do the same. Chris ----- Original Message ----- From: "Spehro Pefhany" To: Sent: Tuesday, November 19, 2002 8:36 PM Subject: Re: [EE]: RS232 <-> 20mA current loop designs > At 06:16 PM 11/19/02 +0000, you wrote: > >A really good way of doing this is to use the "linear" opto-couplers from > >H-P (or whatever they're called this week). The HCNR200 application > >datasheet has excellent circuits for 4 - 20 mA TX and RX. The only omission > >in these designs are the RFI suppression and decoupling capacitors that > >you'll find necessary in the "real world". > > > >The accuracy and linearity possible with these devices is remarkable. > > Why would accuracy and linearity be important in a digital circuit? > > These are the same kind of circuits that used to directly energize a > solenoid in the old Teletype machines, NOT process control type > analog current loops. > > > Spehro Pefhany --"it's the network..." "The Journey is the reward" > speff@interlog.com Info for manufacturers: http://www.trexon.com > Embedded software/hardware/analog Info for designers: http://www.speff.com > > -- > 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 > > -- 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