USB to 3-wire Serial Cables (like AXE027)

[westaust55]

A while back there was "guidance" to test the voltages at the PICAXE end of a USB to serial cable as there should be around -12 volts present before the 22 kOhm resistor.

This is not the case and there is a specific chip available used for such cables.

I have today during some web surfing stumbled across a schematic.
While the attached may not be 100% accurate for the AXE027 US to serial cable, in the absence of an AXE027 schematic this is likely fairly close.

Hopefully this may clarify the position for those in trouble with USB to serial cables in future.

 

[eclectic]

AFAIK, the circuit/schematic is on page 4 of

http://www.rev-ed.co.uk/docs/axe027.pdf

e

Add
and see Technical's post in

http://www.picaxeforum.co.uk/showthread.php?t=5757&highlight=axe027+circuit

 

[westaust55]

AXE027 cable

thanks e.

Seems I only got page 1 when I bought the cable here some months ago.
will save pdf and print out the full datasheet and add to my file of PICAXE info.

note sure how others thought +12/-12V (proper) RS232 level voltages would be present.