Opto-isolated RS-232 for Icom CI-V

First thing I should say, this is my 'design' and I offer no guarantee that it will work for you, be careful if you build one, do your own testing to be certain it's not going to blow up your laptop and or radio, cause a rift in space time and the instant destruction of the entire universe as we know it.

OK, guff out of the way, the Opto Isolated CI-V Interface I mentioned earlier,



And the schematic!
It's rough, hand drawn and there have been a couple of changes to component values, mainly because I found a document that suggests the CI-V interface port on the radio shouldn't have to sink more than 2.5mA, so one resistor has been changed (the 680R on pin 2 of the right hand side opto is now 2K) and another removed completely (the pull up on pin 5 of the left hand side opto) to comply with that.

If I short the CI-V line with my ammeter, I get this:
1.6 milliamps, I'm comfortable with that.

Currently (yeah yeah) it works reliably as a serial loopback at 19200BPS which is plenty of margin because the Icom CI-V bus is, by default, 4800BPS, if I change the 2K to 1K it works fine at 38400BPS but is able to source 3.6mA so YMMV, I don't *think* the 2.5mA is an absolute maximum rating as I've seen CI-V designs that can definitely supply more (and if the document linked earlier is to be believed, some can supply several tens of milliamps) but if it works reliably with the 2K resistor then why tempt fate?

I'm intending to design a PCB to put the COM Port isolator, Optoisolated PTT and Audio transformers on, as a part of that board there will be a prototype area so I can add bits and bobs of circuitry that might become necessary (audio attenuators, bypass capacitors, filter networks etc.) or just desirable (audio amplifier, manual PTT switching, microphone input), I doubt there'll be any interest, I doubt anyone is even reading this but the PCB will probably be one of a batch of ten so there'll be some spare.

Video of it in action here

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