Digital Interface Ver X2

[NZ0I]

The Dual-Band Transmitter power supply board is ready to provide +12V. So I've been working on the Digital Interface board for the transmitter. This version includes WiFi support, as well as on-board FTDI for connecting directly to a computer's USB port.

The board is mostly assembled now. Some blue wires required, but no major rework thus far. The ATMEGA328 processor is up and running, and it can talk to all the I2C devices: the Si5351 clock generator, the MCP23017 port expander, and the DS3231 real-time clock. The RTC can be set and read by the ATMEGA, and is also generating INT0 pin interrupts at 1-second intervals. The INT0 interrupts will be used to wake up the processor (and the rest of the transmitter) at specified times, allowing the processor to shut down most of the transmitter to conserve battery power.

Still need to test the FTDI chip and install the WiFi module. But everything else seems to be functioning.

[NZ0I]

The FTDI chip has been installed and tested on the Digital Interface board, and it works as designed. The Digital Interface board can now be directly connected to a PC using a standard USB micro to USB cable: the standard cable included with many USB compatible devices like cell phones, cameras, 5V battery packs, GPS devices, etc. Using puTTY, or the Arduino serial monitor, one can now issue commands directly to the ATMEGA328 processor. Bootloading should also work, but has not been tested yet.

The WiFi module has also been installed, and after some modifications and software work, it works as intended. The low-power ATMEGA328 processor can power off-and-on the WiFi module as needed to save power, and can communicate with the WiFi module over the serial port.

As an end-to-end test to prove that all components are working on all three processors (ATMEGA328, WiFi module, and SmartPhone) the clock synchronization feature was implemented. Tapping the "Sync" button displayed on an iPad's browser (see http://qsl.net/nz0i/tx.html) causes a message to be sent from browser (over WiFi) to the WiFi module, then (over RS232) from the WiFi module to the ATMEGA328, and finally (over I2C) from the AtMEGA328 to the DS3231 real-time clock chip on the Digital Interface board instructing it to synchronize its time with the iPad's internal clock. Then, once-a-second, the WiFi processor queries the ATMEGA328 for the current time, and after receiving it, sends it to the iPad for display. The iPad browser screen then displays both the iPad internal clock time, and the DS3231 clock time, each updating once per second in synchrony. Result: one-button wireless transmitter synchronization is working.

Now comes the time to assemble and debug the transmitter board.