Since I’ve had my Hermes Lite 2 (HL2) and Xiegu XPA125B amplifier combo I’ve had to manually change the band setting on the amp as I never purchased the HL2 I/O board when I initially purchased the kit.
At the time I didn’t think I would need it but, changing band manually on the amp (and sometimes forgetting causing tuning issues) is a nuisance and so I put my hand in my pocket once again and ordered the I/O board for the HL2.
The HL2 I/O board is a small RaspberryPi Pico controlled device that can be used for a multitude of functions depending on the software loaded. Many people are writing their own software for the Pico to do things like control transverters, remote antenna switches, amplifiers and just about anything else you can think of. It’s a really versatile little add on board for the HL2.
The I/O board arrived after about 10 days from Makerfabs, all nicely packaged as always. Unfortunately due to Christmas, New year and other priorities it’s sat in the box since it arrived.
A couple of days ago I finally got round to getting it out of the box and set about configuring it to control the Xiegu amp.
The Xiegu amp needs three connections from the I/O board. They are PTT, Band Switching Voltage and Ground. These are easily accessed from the I/O board via 3 jumper wires to connect to the DB9 connector on the rear of the board.
The other thing that is required is some software for the RaspberryPi Pico to control the whole process. Steve, M0XVT has kindly supplied me with a copy of the software.
Soldering the jumpers from the relevant points on the circuit board to the DB9 connector was pretty straight forward. You can use any of the pins on the DB9 connector that you like as from the factory the DB9 connector isn’t connected to anything. I decided to use pins 2, 6 and 8 and so will refer to those pins from this point forward.
I used a different colour for each of the jumpers so that I knew which jumper was for which connection. The colours used also match the colours of the wire in the old RS232 serial lead that I cannibalized to make the connection between the I/O board and the amp thus making it easy to ensure continuity.
The colours are as follows:
Black Jumper - Ground - Pin 2 on DB9 Connector
White Jumper - PTT - Pin 6 on DB9 Connector
Red Jumper - Band Control - Pin 8 on DB9 ConnectorThe I/O board gets its power feed directly from the HL2 main board however, the 3 pins it needs to connect to don’t have any headers in place and so, it’s necessary to solder a short row of 3 header pins onto the HL2 main board.
I found the easiest way to do this was to put the 3 header pins into the correct position and then use the HL2 to N2ADR filter board connector to hold them in place whilst soldering. This worked perfectly and I soon had the header pins soldered onto the main board.
It’s important to note that the 3 extra header pins need to be placed 2 holes away from existing header pins as shown above. Take care to get these pins in the right position so as not to cause any damage to the 3 circuit boards once all are connected and powered up.
Note: The HL2 main board must be removed from the case to solder the extra 3 header pins in place. Take care to ensure the correct fitting of the PA heatsink when when refitting the HL2 main board into the case.
At this point I refitted the N2ADR Filter board back into the HL2 case so that the two sets of header pins aligned correctly ready for the placement of the new I/O board that would connect all 3 circuit boards together.
Once the filter board was in place I fitted the new I/O board taking care to ensure all pins aligned with the socket and then gently pushed it home.
The close up of the I/O board connector above shows how the extra 3 header pins connect to the last 3 sockets in the I/O board connector. It’s a snug fit with the N2ADR filter board below it.
Before the HL2 case can be put back together it’s necessary to load the software onto the RaspberryPi Pico (top left in photo above) that controls the I/O board.
This is accomplished by pressing the tiny button on the Pico whilst connecting a USB lead to the USB socket on the board that had already been plugged into my PC. Once connected the Pico appeared as a USB drive on my Kubuntu Linux desktop. All I then had to do was to copy the software file onto the drive. Once the software file is on the drive the Pico will reboot automatically and the little LED on the board will start to flash to show it has booted successfully. At this point I could safely unplug the USB cable.
The software for the RaspberryPi Pico is available for download below.
The I/O board comes with a new back panel for the HL2 to accommodate the extra connectors on the rear. Refit the top of the HL2 case and then attach the new rear panel using the original 4 counter sunk screws.
The final part of this project is to make the lead that will go from the HL2 rear DB9 ACC connector to the Xiegu XPA125B mini din ACC socket.
For this you will need a 6 pin mini din plug (AKA PS2 plug), (these are readily available on Amazon) and an old fashioned DB9 female connector from the days of RS232 serial leads..
The connections are as follows:
DB9 Pin 2 (BLACK) to Mini Din Pin 6 (GND)
DB9 Pin 6 (WHITE) to mini Din Pin 2 (PTT)
DB9 Pin 8 (RED) to Mini Din Pin 3 (Band Switching Voltage)Below are a couple of screenshots from the Xiegu XPA125B user manual showing the Mini Din pin layout and the data interface connections for the amplifier.
Before I connected the lead to the two devices, I tested the end-to-end continuity of the lead to ensure all pins were correctly connected and that there were no shorts between any of the pins.
It’s important that the wires are connected to the correct pins on each end of the lead. Failure to ensure correct connection could cause damage to your HL2 and/or amplifier.
Once the lead had been tested, I connected it to both the Hermes Lite 2 and the Xiegu XPA125B amplifier. I also had to switch the amplifier band switching to AUTO.
Now when I change band on my HL2 in the PiHPSDR software the amplifier also changes band at the same time keeping the two devices in sync. No more manual band changing for me!
I hope this article is of use to other Hermes Lite 2 users who have purchased the Xiegu XPA125B but, have yet to setup auto band switching between the two devices.
Thanks to Steve, M0XVT for all the jumper information and the RaspberryPi Pico Software to get this all working.
UPDATE:
The RaspberryPi Pico software originally came from Ramon, KP4RX. More information can found in this Google Groups article where he released the binary into the wild.
A full table of I/O resources available on the HL2 I/O board can be found on the KP4RX Guthub page.
The source code for the main.uf2 file above can be found at KP4RX.com
More soon …
