Jon's Imaginarium – Isolated USB-UART Interface using CH340

[Visitor]

In some circumstances, it is desirable to use an optically-isolated USB-UART interface. Examples might be where data from AC line power monitor is desired. The computer's USB port is referenced to ground, while the power monitor's UART lines may be floating at AC line level. To prevent shock hazards and damage to the monitor and PC, isolation should be used.

I developed this circuit to monitor 70s-technology aircraft aids to navigation where any glitch caused by connecting a PC would have dire consequences. Optical isolators isolate the UART data lines, and are powered from the test device.

The CH340 USB interface is powered by the PC. Power, ground and data lines have no connection between the monitored device and PC.

 

[Pommie]

Personally, I appreciate these posts, they keep me thinking. Keep them up.

Mike.

 

[JimB]

Is it just me, but I can barely see the the lines in that schematic.

JimB

 

[Visitor]

Is it just me, but I can barely see the the lines in that schematic.

JimB

You're right. Sorry. It's a tradeoff between image resolution and line visibility. I'll try again today.

 

[Ian Rogers]

As I use a laptop, I just tilt the screen and all the lines appear..

 

[Visitor]

This schematic should be better.

 

[JimB]

As I use a laptop, I just tilt the screen and all the lines appear..

If I tilt my desktop screen, most of the lines are better but still poor.

This schematic should be better.

Yes it is, most readable.
Thankyou

JimB