The Bill-of-Material (BOM), schematic, and build instructions for the CTR2-Mini Antenna Switch Controller can be found below. There are links on the BOM spreadsheet to locate parts on You can use the part #s to find these parts at other part suppliers. Click the Download PDF button to download the file.

Bill of Material

Mouser BOM

I have also created an automated BOM on for this project. This allows you to easily order the through-hole components and a Wio Terminal to build the antenna switch controller. You can order the PCB (with all SMT components pre-installed) and the optional enclosure kit on my CTR2-Mini order page. The PCB kit comes with the main board and the Wio GPIO Interface board. The enclosure kit includes the pre-assembled acrylic stand shown in the lead photo plus a 1.3″ black knob, four push button switches and five DuPont jumpers for the function keys, the board mounting hardware, and four silicone rubber feet.

Mouser: CTR2-Mini Antenna Switch Controller v1.1

Interactive BOM

I’ve also created an interactive BOM that is very helpful when assembling this project. Just unzip the HTML file and open it in your browser. It also gives you a good idea of what needs to be done to build the ASC. Just select the Front View.


The schematic for the antenna switch controller can be downloaded below.


Construction of the antenna switch controller is pretty easy. Only the top through-hole components need to be installed. You should be comfortable soldering header pins on .1″ centers. All the SMT components are pre-installed on the bottom of the PCB so no worries there.

LED Placement

The LEDs indicating the selected antenna relays are grouped together (i.e. A1 and B1, A2 and B2, etc.) The PCB is laid out so that the A LEDs are one color (red) and the B LEDs are the opposite color (green). This helps distinguish the active antenna relay for each port.

If you are going to use the ASC on a 1×8 antenna switch you may wish to have all the LEDs the same color. In this case, simply insert the B LEDs opposite the A LEDs when you install them. The square pad on the LED track indicates the anode (the longest) lead.

Function Keypad

You a few options for the function keypad.

  • Install the buttons on the optional enclosure I can supply (as shown in the lead photo). To do this:
    • Wire each button using a DuPont jumper to J7, a 5-pin .1″ header. Connect one terminal of all four switches to GROUND (J7 pin 1). The other terminals are connected to the other pins on J7. Switches and jumpers are supplied in the ASC enclosure kit.
  • You can choose to locate the encoder and function buttons in a separate enclosure. This assembly connects to J3 on the ASC (a 4-poll 3.5″ phone jack). You’ll need the appropriate shielded cable to connect the remote encoder/function buttons to the ASC. The push buttons on the remote pad will need pull-down resistors as shown in the schematic below.

Power Options

There are several power options on the controller.

  1. Connect an external switch to JP3. The BOM has a rocker switch that fits the acrylic enclosure that I can provide. You can use any switch you want for your enclosure or you can install a jumper here to keep the ASC powered on all the time. You can use the Wio’s power switch to turn it off.
  2. Power to the external antenna switch:
    • Strap JP6: 1-2 to provide power to the external antenna switch when the ASC is turned off (it has latching relays). This will keep your antennas active all the time.
    • Strap JP6: 2-3 to provide switched power to the external antenna switch. Your external switch will go offline when you turn the ASC’s power off.
  3. Power Polarity to the external antenna switch:
    1. Strap JP4 and JP5 1-2 to provide +12 VDC to each control lead to the external antenna switch. Ground (return) is supplied on pin 9 of the DB9 connector.
    2. Strap JP4 and JP5 2-3 to provide Ground to each control lead to the external antenna switch. +12 VDC (return) is supplied on pin 9 of the DB9 connector.

Ribbon Cable

Build a 16-conductor ribbon cable to connect J4 on the main board to the Wio GPIO board. Build this cable after you have completed the main board and have it mounted in the enclosure.

Expansion Board

Two control boards are required to control a dual-port 8 antenna (2×8) external switch. One board will be the main controller and the other will be the expansion controller.

Build the main controller as shown on the schematic. Populate J2 and J4 with 16-pin ribbon connectors.

On the expansion board:

  1. Cut JP1: 1-2 and JP2: 1-2 (PCB pads). Make sure they are open.
  2. Solder bridge JP1: 2-3 and JP2: 2-3
  3. Install only J2 on the expansion board
  4. Build a 16-conductor ribbon cable that is long enough to connect J2 on the main board to J2 on the expansion board.

Connect the DB9 connector on each board to your external antenna switch as follows:

  • Main DB9 Pins 1 to 4: Connect to relays A1 to A4
  • Main DB9 Pins 5 to 8: Connect to relays B1 to B4
  • Expansion DB9 Pins 1 to 4: Connect to relays A5 to A8
  • Expansion DB9 Pins 5 to 8: Connect to relays B5 to B8
  • Connect Pin 9 on both DB9 connectors to the return on your external antenna switch.

I hope this project sparks some interest in you. It’s pretty easy to build. As always, if you have any questions please contact me,

73, Lynn, KU7Q