5 Band CW QRP Transceiver Clock and Control Board

Written on 30 July 2021

Part of the 5 band transceiver.

The clock and control board is the heart of the transceiver containing the ATtiny 3216 microcontroller and Si5351A clock generator chip. It generates quadrature clocks for the Tayloe detector in the receiver and the transmit clock for the class E PAs. It also controls the display, morse keyer, transmit/receive switching and so on. Clock and control board schematic

J1 takes 12V in, D1 protects against reverse polarity, U2 is a 5V regulator (for the microcontroller and LCD) and U3 is a 3V3 regulator for the clock chip. Q1 and Q2 are bidirectional I2C level shifters to convert between 3V3 and 5V. The ATtiny3216 can run at 3V3 but the LCD requires 5V.

J2 and J3 are pin headers for most of the I/O pins on the microcontroller. See below for where they connect. J4 is for the LCD taking 5V and the I2C bus.

J5-J7 are SMA sockets and J8 is a pin header for the 3 clock outputs. I only use J8. CLK0 and CLK1 connect to the direct conversion receiver board and CLK2 goes to the TX boards.

Pin Function
PA0 UPDI (Rear panel update socket)
PA1 Serial TX (Rear panel CAT port)
PA2 Serial RX (Rear panel CAT port)
PA3 Sidetone (Phasing audio filter and amplifier board)
PA4 Morse paddle dash (Front panel paddle socket)
PA5 Morse paddle dot (Front panel paddle socket)
PA6 Transmit (TX boards)
PA7 Receive enable (Phasing audio filter and amplifier board)
PB2 Relay 4 (20m TX board)
PB3 Relay 0 (80m TX board)
PB4 Relay 1 (40m TX board)
PB5 Relay 2 (30m TX board)
PC0 Pushbuttons (Front panel)
PC1 Relay 3 (60m TX board)
PC2 Rotary encoder A (Front panel)
PC3 Rotary encoder B (Front panel)

Rotary encoder and other connections

I found that connecting to my PC’s serial port with a cheap USB serial adapter introduced a lot of noise into the receiver. The proper solution would probably be to use an opto isolator but I found that adding 10K resistors to the connection cured it. Even the earth connection was noisy.

The three front panel pushbuttons are connected to PC0 configured as an ADC input.

Next article - Direct conversion receiver block