ASW12V

Remote controllable multi-channel AC/DC switch
ASW12V: antenna switch for 12V

My shack has a number of 12VDC controlled circuits for antennas. When I am sitting at the operating position, they are controlled by rotary switches there. When connected to the station remotely using WriteLog, I need a way to control the switches from the shack PC. This device is a USB controlled solid state multi-channel AC/DC switch. While its named "12V" the solid state relay (SSR) outputs can safely switch up to a maximum of 60V AC or DC, and at up to about 3A. The remainder of this document uses "12V" to describe the power supply, even though the PCB is more capable.

In the absence of control commands over its USB serial port input, its output channels follow its input channels. USB power on the USB-C plug is required to power the embedded microprocessor for it to follow its inputs.

This device is controlled by ASCII command strings sent over its USB serial port. WriteLog is not required to operate it, but a WriteLog plugin is posted here showing how to embed antenna switching commands for this hardware within WriteLog. The example has on-screen controls corresponding to the antennas at W5XD. Source code is published.

The power and ground are optically isolated on both input and output side, and separately, into groups of four channels. Each group of four has its own power and ground terminals. All the input and output power and ground circuits are optically isolated from the USB power and ground as used by the Arduino controller on the PCB.

Revision 8

This documentation is for Revision 8 of the ASW12V. Previous revisions of this design used PNP darlington output devices. This SSR design reduces the parts count, and enables both sensing and controlling AC as well as DC circuits. See the git tag "PCB-REV05" for the documentation for the version using the STA402 PNP darlington outputs.

Here is the 24 channel version built with wired connectors:

The longest dimension is just less than 8 in (20cm). The short dimension is about 2.5in (6.2cm). The 12 channel version is half as wide (4" x 2.5" or 10cm x 6.2cm). Here is a populated PCB before connectors are installed. the SMD components are all on the "bottom" of the PCB and the connectors and QTpy controller (which are through-hole) are installed on the "top".

Top and bottom are in quotes because when the SMD components are installed, they must be on the top of the PCB in the oven. But when the full device is assembled and in operation, the SMDs are on the bottom.

Power and Ground

The PCB layout has three sections each with four input/output channels and with grounds and VCC isolated to that section. In the photo above, all the G and 12V connections are, without installing any jumpers, isolated from each other. Solder jumpers on the PCB enable interconnects among them. See below. The power and ground circuit is this: ASW12V-circuit3.pdf. Many different power supply options are supported by jumper options on the PCB for exactly what Ground and VCC connections are interconnected on the PCB. One thing that is not optional: fuse at about 3A or otherwise current limit the connection from the power supply to the Vcc terminal on the ASW12V. The ASW12V PCB has components too dense to service. Plan on replacing it if it is damaged by over current.

You can successfully use this device with NONE of these jumpers in place. But consider how you want to use it. In my own case, the same 12VDC supply powers all my antenna relays, so I can safely tie all the Gnd and VCC terminals together. Your shack may differ.

The PCB has jumpers that can internally connect:

1. the VCC pin to the VCC on the adjacent section.
2. the OUTPUT GND pin to the OUTPUT Gnd pin of the adjacent section.
3. the INPUT Gnd pin to the OUTPUT Gnd pin of the section.
4. the INPUT GND pin to the INPUT Gnd pin of the adjacent section.

The positions of the jumpers are hand-outlined on this bottom view of the PCB silkscreen. The jumpers are most easily installed (and removed) on the bottom side of the PCB. The jumpers corresponding to (1) and (2) are at the top of the picture, the ones for (4), the INPUT to INPUT, are at the bottom and the ones for (3) are between.

The circuit board traces are wide enough to suppoart a total of 3A to the VCC and GND connectors on each terminal block.

Construction

A parts list, construction details, and a PCB layout are published here.

Inductive Loads

The solid state relays do not have built-in protection from any inductive voltage spike that happens as an inductive load is turned off. The PCB has 12 positions for diodes to be installed, labeled D11 up through D44. Installing these diodes is optional. They are not needed for non inductive loads, nor for inductive loads that have their own flyback diodes installed (e.g. the Array Solutions 6-Pak in my shack.)

Controlling the ASW12V

A USB connection to the USB-C connector is required for operation of the microcontroller. Without USB power, all outputs are off. The sketch on the Arduino powers up in a pass through mode. That is, the firmware transfers the INPUT side as a pass through to the OUTPUT—a signal on an INPUT pin results in Vcc applied to corresponding OUTPUT pin on the opposite side of the box.

When plugged in to a computer, the drivers for its USB port automatically are installed (on most operating systems) and create a virtual serial port. An example program to write useful serial commands is published here on github. The example is specific to the antennas to be controlled at W5XD. It doesn't put much on the screen. as not much is required at W5XD.

Control the beverages, one to the RX antenna on each of two radios:

Control the main transmit antenna, one of 6 to each of two radios:

All the buttons on the two windows above can be programmed as keyboard shortcuts in WriteLog.

Enclosures

This repository publishes a design for an enclosure a 24 channel device (with 2 PCBs) with connectors installed on the PCB. The 3D designs were done with Solid Edge. The PCB hole pattern accommodates either the screw terminals or the connector. The Solid Edge models are in the CAD folder. The 3D printable parts are published in the STL directory. Unfamiliar with 3D design and printing? Don't be bashful about clicking the STL link and the enclosure models.

I use a prusa3d printer.