---------- Original Message ----------
From: VE3VXO <ve3vxo@...>
Date: November 15, 2020 at 12:30 PM

It's not complicated.? An optocoupler has an LED on the input side and a light activated transistor or FET on the output side.? They are electrically isolated and the transistor is turned on solely by the light from the internal LED.?Some typical optocouple candidates are (there are many options) TIL-111, CNY17 etc.? Looking at the QCX+ schematic the PTT line comes from the IC3D pin 11. If you connect to that signal at JP22 run a wire to the cathode of the LED in the optocoupler and then you want to limit the current through the LED so you need a series resistor.? The LED is going to take about 1.6v check the datasheet from you optocoupler for Vf and also not the current they show under the test conditions but it will usually be around 10 to 20mA.? Let's assume 10mA for this discussion.? If you run the resistor from the anode of the LED to +5v to get the needed resistor value it's only ohm's law.? Subtract the Vf of the diode and you've got 5v-1.6v = 3.4v on the resistor.? So for 10 mA you would need 3.4v / 0.01A = 340 ohms.? Use 330 ohm standard value and call it good.? The output side of your optocoupler if it is a bipolar transistor use the collector to the PTT on your amp and the emitter to the GND on your amp.? If FET output it doesn't really matter but put drain to PTT and source to GND and you are done.? If you have the experimenter's mezanine board in your QCX+ it would be an ideal place to put the optocoupler.? One note, if you add a RCA jack on the QCX+ for this purpose get the kind where the outer shell is not connecting the chassis. there are some jacks that have a plastic mounting and the shell is isolated otherwise you could drill a larger hole to clear the connector, mount the connector on a scrap of plastic and rivet the plastic to the back of the chassis so the RCA jack protrudes through the hole which will keep both of the output side connections of the optocoupler isolated from the QCX+ chassis.?? Does this make sense?.....Joe

---------- Original Message ----------
From: nz0tham@...
Date: November 15, 2020 at 11:17 AM

Sounds complicated!

?

?

?