First step, add a jumper to route 3.3V the I2C input connector (Tnks, Tony, for adding this connector… this is a smart idea)
The jumper is located under the tip of the red probe…. the output on left hand side, the input on either 5V o 3.3V terminal.
The 5 Volt option was originaly used to power Tony’s USB/I2C interface if you choose to NOT use the one delivered by the USB plug of your computer. This option was avoiding the risk to add another ground loop between the SR and the computer.
The HP AN97055 application note gives details on the way we can build such an interface. As we have the two Vcc references (one comming from the computer via the USB plug, the other comming from pin 1 of the I2C SR connector, we just neet to print a PCB to hold those 4 FET transistors.
As I’m using Dave’s interface
and a couple of insulating Triad audio transformers
it would be smart if I could put all this stuff on the very same board…
transistors and transformers will be located on the main board, with WB6DHW’s interface in piggy back. Just the time to learn how to use Kicad… and it’s done.
I draw a quick and dirty project with Express PCB
Dave’s pcb will be soldered at right angle on the upper side of the circuit (double side, uperside left as is, excepted vias)