CAT cable for Alinco DX-77 / DIY ERW-7

[MikeSierra]

Instead of paying ~50 quids for the Alinco ERW-7 cable for CAT control of the DX-77, I built my own with cheap parts.
Parts used:
Chinese CH340G USB to TTL adapter, from aliexpress.
BC557 PNP bipolar transistor.
Two wires 0.5mm2.
3.5mm stereo jack.
Short piece of heat shrink tube.

How the Alinco serial port works:
3.5mm stereo jack.. Sleeve is ground. Ring is RX and TX. Tip is not connected.
RX/TX line has a pull-up resistor inside the radio, setting the voltage to approx. 4 volts. When the PC or the radio is "talking", the line is pulled down to form the zeros and ones.

Small problem.. The CH340G USB to TTL stick has a 1.5k series resistor on TX output, leaving it without "juice" to pull the line down enough for the radio to interpret the low level correctly. Solution is to let a transistor do the pulling.

m_20210523_091130.jpg

m_20210523_090545.jpg

This works with my Alinco DX-77. It did however not work with Alinco DX-R8 - DX-R8 leaves low level signal at one volt, which is too much for the USB stick to read correctly (Not all Alinco radios are created equal).

[MikeSierra]

Here is an oscilloscope screenshot from RX/TX line while trying to read settings from Alinco DX-R8 communications receiver.

Screen Shot 21-05-23 at 10.44 AM.JPG

First comes the command string from the computer. It is then followed by an answer from the radio.
The answer from the radio does not go lower than ~1.2 volts, which is over the threshold for the USB to TTL adapter.
Any suggestions on how to get it working?

[MikeSierra]

CH340_schema.jpg

LEDs D2 and D3 with series resistors are pulling up the voltage.
The LEDs needs to be removed.

[MikeSierra]

I removed LEDs D2 and D3 and now it's working with Alinco DX-R8 also.

[MikeSierra]

For this adapter to work with DriveR8 control program, hardware flow control function CTS needs to be disabled.
EDIT: this is likely to change in the near future.
That is done by connecting CH340G pin9 CTS to pin1 GND.

[simeonGR]

Dear friend thanks for your instructions.I have a question, i have available FTDI FT232RL USB to TTL.Can i use it?Will it work?


Thanks