various DATV transmitters. The two relay boards and the
FPGA board were bought on eBay from China. The Veroboard
has an RS232 level converter chip on it. The whole thing is
controlled via a serial link. R001
and R150
as the amplifiers are some distance from the computer and
USB2 wouldn't cut it. I have implemented a simple rx UART
in Verilog which runs on the FPGA board. I may add ADC
support later so I can measure temperature, power, VSWR etc.
Using an FPGA seems a bit like overkill in this application
but the boards cost about the same as ready made PIC boards
if you are careful in your purchasing and of course they have
far more I/O on them than a PIC would have.
When I send the commands from my Linux system I can hear the
relays clicking and the right ones come on, so I know it is working.
Next I have to do some rewiring of the transmitter rack
to accomodate the new relay box. I have amplifiers for 70 cms,
23 cms, 13 cms and 9 cms so there is a lot of cabling to add.
DATV-Express is in the hands of the PCB layout guy so I have a
window to sort out my own stuff at the moment.
Hi Charles,
ReplyDeleteI was contemplating I2C instead of RS232 for similar application (temperature and Ibias reads/sets from/to remote and mast-mounted PAs).
Surprisingly I2C can work up to 50 meters (NXP App Note AN444).
Benefit is that it is a bus and so can talk to multiple devices. (And that with so many I2C ICs out there functionality (e.g. temp sensor, ADC, DAC, relay control) is added easily and cheaply to a project. Might even think of setting the frequency of a mast-mounted VCO/PLL from within the shack.
Herman, PE1GTA
Hello Herman,
ReplyDeleteI hadn't really thought of using I2C.
DATV-Express uses I2C to communicate
between the FX2 controller and the
PLL/modulator.
I am going to add an I2C slave Verilog module
inside the FPGA so I can send interpolation
settings and I/Q correction values to the
FPGA from the P.C via the FX2 controller on
the board.
We already bring the I2C bus out to the edge
connector on the Express board to allow the
sort of things you are intending to do.
- Charles