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

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

Post by 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).
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MikeSierra
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Posts: 23
Joined: 19 Feb 2017, 08:55

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

Post by 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?
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