Project Yamhill Front Panel Rev B PCB
And other Rev B board updates
As Project Yamhill nears actual physical implementation, it’s time to start building some more real-time, two-way communication. We’re starting to get some beta testing and discussions going! If you’d like to participate in Project Yamhill chat, please click on the link below. Thank you!
In a bit of housekeeping up front, I can now tell a little more about the personal stuff that I was dealing with at the time of my last post. Due to some failed negotiations, I’ve decided to part ways with my current employer and pursue a different work opportunity. This new job is work-from-home, pays a fair bit more than my old job, and has flexible work hours (which is really critical for me). Overall, this should be a great thing for my family and also for Project Yamhill, as I will need even more funding to get this projecting going to the next level.
The drama in dealing with all of this took me away from my work on Project Yamhill and other Etherkit stuff a fair bit, but once I make the transition to the new job by the middle of June, the pace of things should pick up a bit more again.
Project Yamhill Front Panel
This board went through the most significant changes, and thus took the most amount of effort to respin, by far. In the interest of not boring the reading audience, I’ll present you with a bullet list of the significant changes for Rev B, excluding any bug fixes:
The audio amplifier had another gain stage added to give some more oomph to the audio without trying to push the remaining stages into too much gain. This should give more than enough headroom for any application.
A full-wave detector circuit for the audio signal consisting of two more op-amp stages plus a couple of Schottky diodes, and another op-amp buffer stage was added. The output of this circuit is now run to one of the slower/higher-precision ADC pins so it can be used for S-meter purposes. There’s also a pin header on this output for potential use in an audio-derived AGC.
Two discrete DAC ICs were added to give the front panel the capability to be connected to a quadrature sampling exciter for future SDR usage. I still plan for the I/Q input from a quadrature sampling detector to go directly to ADC pins on the RasPi Pico.
The power subsystem for this board was completely redone. A lot of digital hash was getting into the audio system of the Rev A board. In order to try to better isolate the audio system from the digital circuits, all of the digital circuits on the board are now powered by independent linear voltage regulator ICs.
All of the pin headers that were grouped together by function have been changed from one large header to individual 2-pin headers.
Project Yamhill Power Distribution
The Power distribution board was tweaked a bit to change the 3.3V switching regulator to a linear regulator. There’s no need to optimize this project for current consumption, so best to go with a tried-and-true linear regulator part.
Project Yamhill Active AF Filter
I’ve mentioned the Active AF Filter changes in a previous post, but to briefly reiterate, I changed this board to use two 8-pin op-amp packages instead of one 14-pin package. It’s hard to find a good audio-quality op-amp in a 14-pin package. I also created a custom footprint that will allow the use of either a PDIP or SOIC package op-amp, which will open up the board to the use of many of the newer, and better performing ICs.
EtherKeyer Mini
The EtherKeyer Mini Rev A board worked pretty well, but it did need a few minor tweaks. Firstly, I changed the keying transistor from a 2N7000 (MOSFET) to a 2N4401 (BJT) after discovering that the 2N7000 could not always properly key every transmitter that I tried it on. Specifically, I believe that the low-voltage microcontroller used here just couldn’t fully turn on the gate of the 2N7000. Changing to a 2N4401 driven with a relatively low-value base transistor did the trick. So that needed a bit of a tweak.
Next, I removed the circuitry to allow the board to be powered from an optional UART 5 volt supply pin. In testing I found that EtherKeyer Mini could run for about 3 months off of one fresh CR2032 cell once I got the power saving code in the firmware nailed down. I just don’t foresee much of a use case for this device being connected to a PC long-term. However, I did add a small pushbutton power switch to allow the user to still save power if the device is idle for long periods of time, like being stuffed in a portable radio kit or something like that.
Party Line 80 Transceiver
The last post from this publication was all about the changes to Party Line 80, so I won’t reiterate that here.
Party Line 80 Refinements
I mainly wanted to show off the rendering of the Rev B PCB since I neglected to do that on the last post. I’m excited to get this and EtherKeyer Mini fully squared away, ready for beta testing in the very near future.
What’s Next
By the end of this coming week, I plan to export the Gerbers for all of the above boards, do one last check of them, and then send them out for manufacturing. I may have one more small secret project going out at that same time…
After that, the plan is to spend more time refining the EtherKeyer Mini firmware, in order to hopefully reduce the code size a bit more and fix a few corner-case bugs that I’ve found pop up. If either this keyer or the Party Line 80 CW transceiver sound interesting enough to you that you may want to beta test them, then stay tuned to this publication for the chance to do that soon.
Congrats on the new day job, and good (steady) progress on the various elements of Project Yamhill.
Congratulations on the new job!