Teensy 4.1 RF Wattmeter and Band Decoder Combo Build Details

Below is the pinout chart for my Teensy 4.1 wattmeter + band decoder build. My equipment to control looks like this:

NOTE: This was written before a PCB was designed in March 2021. The info is still generally useful. See more recent articles for the PCB build notes.

1. Using a 5 band transverter covering 144 through 1296Mhz. Uses up to 5 lines input, default is BCD so only the first 3 or 4 really change. My old stack of transverters were similar. This 5-band Xvtr is located outdoors in large weatherproof boxes with the amps and antennas.
2. 2x 28MHz IF cables (split RX and TX at 1mW drive) and a control cable (band decoder - 4 wires + PTT + GND + spare) runs from the shack to the boxes.
3. Amplifiers for bands 144 to 1296 are located outdoors near the transverter and connect to each transverter output.
4. Bands 144, 222, 432, and 903 connect to several SPDT coax switches to share a common 144-1296 LPDA antenna 30 feet away.
5. 1296 amp is direct connected to its own antenna
6. In line with each antenna cable leaving the boxes is a Bird Line section. Normally I would use a bi-directional coupler for SWR calculation but I had several line sections and a Peak reading panel mounted Bird meter so using them this install.
7. A 12VDC high side drive (so common ground) SP6T coax switch connects an antenna Bird line section output to the peak reading meter input.

The Band decoder needs to:

1. Receive the Radio's Band Decoder 4 line BCD (5V) and PTT (9V) signals.
2. Pass on the Radio's band decoder BCD output to the transverter (5V).
3. Pass on the Radio PTT line to the transverter (5V).
4. Select the right Bird power meter coax line section for the current band.
5. Select the right antenna for the current band.
6. Apply 12VDc to the amplifier for the current band to signal it to power up.
7. Send PTT to the Amps via a 5V opto-coupled relay module. PTT lines from each amp are diode isolated and all connected together at the relay. This works since only 1 amp is ever powered on at a time.
8. Remote LNAs will be switched by amps own sequencer if needed.
9. Optionally insert a custom delay on PTT release and PTT start to the transverter.
10. Display the port status for PTT, Band-In pattern and Port A, B, and C output patterns on a OLED screen at the CPU.
11. Not using OTRSP in this install as the radio and Decoder are handling all custom decode control patterns.

The Wattmeter needs to:

1. Read the Bird peak reading meter output level as the Forward power level, calibrated for each band.
2. Send the meter results to the Desktop app over extended USB.
3. Communicate with a Nextion touchscreen via USB serial. The PC will bridge the serial data to a local Com port with USB Serial TTL converter on a local Nextion screen in the shack. The wattmeter itself has a small OLED display for read only status. Also displays current band. Ref and SWR fields were removed from the OLED display since they are not used.

Build wiring:

I assigned IO pins on the CPU to make wiring to connectors easier when possible. Each pin is mapped so you can mix them up any way you need, code does not care. I only needed 4 input lines for BCD (Radio is a Elecraft K3 so 5V via weak pullup resistors = 1, and <1.0VDC = 0. 1 PTT input (9V, TX=GND) from my radio. The CPU is 3.3V so level translation is required.

Port A passes the BCD on to the transverter with Port A in Transparent Mode. The Teensy is a 3.3 V CPU so voltage translation is required. Using a ULN2803 module with some resistors to do that. BCD for the transverter is 5V and GND levels.

PTT Polarity is set to Active LOW on both the input and output. The 5 band transverter PTT voltage for RX state is 5V, GND for TX state.

Port B is used to control 6 of the 8 opto-coupled 12V relays, one for each of the 6 bands (50-1296), via a ULN2803 driver chip. The NO and Common contacts close when selected to send 12VDC to the amp for remote power-on.

Also on the Port B relays are connections to the Power Detector SMA SP6T coax switch. This SMA SP6T coax switch input control pins are +12V with common ground. I have Bird Line Sections installed in each antenna cable and a Bird peak reading wattmeter with a buffered 2nd output, the first port goes to a local analog meter mounted with the amps. Since 4 of the 6 bands controlled here are using the same antenna for now, those 4 bands (144, 222, 432, and 903) are wire-OR'd via diodes. The cathodes are connected together and drive pin2 of the SMA switch. 1296 drives pin 3. 50Mhz drives Pin 1.

PTT Output drives a single relay module. The relay outputs ground on TX and connects to the transverter PTT input and to all of the amps via a Wire-OR'd connection using diodes. This works since only 1 amp is ever powered on at a time.

Not using Port C at this time.

Here is the "motherboard". All IO drivers and level translation are on PCB modules off-board. They eventually go to back panel connections.

The pin assignments: