Hi Kx3 users,

Other posts have previously dealt with the issue that the standard KXUSB 
cable for Kx3 does not support CW keying from the computer to the Kx3 
radio, simply from the fact that as opposed to the ordinary serial 
connection (old RS-232 standard), the RTS and CTS pins are not available 
in the 3.5 mm, three-pin TRS jack connector for ACC1 in the Kx3.

Pursuing this further, and not wanting to have more than one USB cable 
to my PC from my Kx3 for all of my buisness on the PC side, I want now 
to build a new interface cable using a custom cable assembly from FTDI:

http://www.ftdichip.com/Products/Cables/USBTTLSerial.htm

Then using either RTS or CTS flags in my PC's radio interface setup (log 
program Win-Test) to pull the CW key connection in the Kx3, possibly via 
a FET or Opto Coupler.

- I have a 4N25 in mind for this ... with parallel coupling of two 
1N5711 to the paddle dit's and dah's.
I did the very same thing on my K2, and it worked like a charm.

Checking the signal levels on my oscilloscope today on the ACC1 data 
connection, I find:

Tip connection = Rx data from the computer to the Kx3 = 5,0 - 5,2 volts 
level (generated by the FTDI line driver)
Ring connection = Tx data to the computer from the Kx3 = 7,0-7,5 volts 
level (generated by the Kx3 line driver)
both with respect to GND being the sleeve pin of the ACC1 jack plug, and 
looking pretty, noise-free and free of any transients. Good, nice square 
signals with good integrity.

Baud rate of the data here is obviously configurable, and with your PC's 
logging program so is the polling rate of how often the PC requests data 
from the Kx3.

My question :What is the "official" Elecraft electrical specifications 
for the ACC1 interface ???
What voltage levels for Rx and Tx, respectively, and what impedance to I 
terminate with when I interface with e.g. opto coupler for my project ?

Would I be OK assuming I just use a 5-volt TTL-level cable version here, 
both ways Rx+Tx OK ?

TTL-232R-5V:
http://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_TTL-232R_CABLES.pdf
 


73'
Brian OZ2BRN
Kx3 # 1118, K2 # 6936 (to which I did the same mod)
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