Schematic Rev B.23

[NZ0I]

I've uploaded a new project schematic (Rev B.23) to the shared Google Drive. The new rev includes the "hybrid" 80m transmitter design, slightly simplified compared to the SPICE model shown in an earlier email. The full 80m transmitter seems to model OK for me, but it would be good for other(s) to confirm.

The last sheet of the schematic now contains the power supplies (some optional) for the transmitter, the 2m SWR bridge, and a real-time clock. That would seem to almost round out the transmitter design except for the following:

1. A very simple mechanical UI - A pushbutton switch, a (multi-color?) LED, and a master on/off switch?

2. An FTDI interface compatible with https://www.adafruit.com/products/70

The first item, a rudimentary UI, needs some analysis and decisions to be made regarding how the user will control and interact with the transmitter in the field. Obviously the operator must be able to turn the transmitter on, turn it off, and probably get some feedback from the transmitter regarding the transmitter's status: programmed settings, battery charge level, antenna SWR, etc. Blinky LED patterns of different colors might be all that is needed to confirm to someone placing the transmitter in the woods that everything is working right, or that something specific is amiss. A short radio transmission (with the final amplifier disabled) might also serve to communicate the same information through a handheld receiver held close to the transmitter. Other ideas?

Configuring the transmitter (and programming it too) will be done using a more sophisticated interface. A Control Head (like the one designed for the receiver) could be used to configure the transmitter's various settings (time interval, power level, ID, clock time setting, start time, stop time, etc.) The same might be accomplished through an attached laptop or cell phone; and that is what the second item is for: the FTDI cable.

The second item (FTDI cable) needs investigation and analysis. The FTDI cable seems right now like THE way to go to provide a computer or cell phone interface to the transmitter. Rather than adding the cost of a USB-to-serial converter to each transmitter, a single FTDI cable would do the job more cheaply, with little impact to the transmitter design (I think). A special interface device supporting TCP via wifi (commercial devices are available) should make it possible to interface the transmitter to any smartphone running an appropriate app, making a very convenient way to configure the transmitters at home or in the field. More investigation, analysis and design is needed to determine if/how that should work. It appears that most of the work will involve software, but the hardware support must be there if it is going to work.

The entire transmitter design needs to be looked at closely, and modeled more thoroughly, before it will be time to lay out the first transmitter board. This is the perfect time to find problems, and to support new features... it is always easier to change a schematic than to cut copper traces and run blue wires. The transmitter design has come a long way in the last month.

With the Rev X1 receiver boards here, and most of the parts for populating them, I will turn my attention back to the receiver for a while. Those wishing to dig into the transmitter design are encouraged to do so. Let me know if you would like any suggestions for areas to focus on.