Nothing revolutionary here, just using bits i have sitting doing nothing. QPRlabs si5351, nano, oled and encoder make up the frequency generation module for my test bed. I have the next one mostly done also, the audio amp.
Ok first off, there is no full schematic for this board, I have already moved on to adding new stuff to it and changing how some parts of it work so I can add in new features. So the best i can offer is this extract that shows where the pins on the micro go to.
Secondly, I wont be releasing my code, the reason is that I do not program using the Arduino IDE and teaching everyone how to program in GCC, to install all the tools required, and uploading the code using an external programmer is beyond my ability to teach anyone let alone everyone. There are just to many things that can and will go wrong and it will only make my life miserable trying to help everyone.
That said, the ESP32 can be programmed in Arduino and the actual basic code is not that hard to write yourself. Turn a encoder and it steps through the relay combinations.
With these relays, I would not put much more than 50w though them. Though the data sheet says they will take 1A but that makes them marginal at 100w. As it stands I think 50w is a very safe bet.
Relays: Omron G5V-1 5V subminiture.
Transistors: PDTC114ET pre-biased SOT23
Caps: 1206 or 1210 Ceramic Multi-layer 1Kv or higher rated, for tuner, 50V 100nF for bypassing. 1uF across the coils of the relays.
Voltage Regulators: 5V and 3.3V 1117 variants SOT223 package.
Toriods: T68-2 T50 would be suitable also, its just what I had, 2,4,8,12,20, 24 and lots of turns.
Top side of the board as 3d rendered.
Bottom side of the board, 3d rendered.
The board as built by me.
Now i mostly work in SMD and design board for things I would like to test. But i do have a lot of through hole parts still that are sitting there pretty much doing nothing, so I started thinking of ways I can use them up and I think I have a solution. Anyway, I have a whole bunch of ideas I would like to try, different circuits to built, test and assemble into working transceivers. Back in the day, which day, ummm, ye olden day LOL, hams would breadboard circuits using actual breadboards. My idea here borrows on that concept and brings it into the modern age.
Starting with the baseboard, rather than mums old chopping board we have a PCB that has 2 power rails for 12 and 5v, a bunch of bypass caps, a DC barrel jack for power input and a 5V regulator. Lets face it, most of what we do only has 2 power rails and those are the most common. Along the baseboard we have 2 rows of dual 10pin headers for our plugin modules to slot in and out of. Each header has 2 power, 2 ground and 6 unused pins for moving signals between the plugin board. Making for neat and tidy wiring.
The prototyping module boards connect to the baseboard with right angle header pins. Either dual or single row header pins can be used, I used single row so i can easily wire stages to the header pins for routing between board on the baseboard.
The tops of each board can be locked together using brass standoffs. This makes for a modular system you can plug and play, mix and match different circuits for testing and characterization.
The backside of each module board contains grounds top and bottom as well as power buses on each side to make veroboard type prototyping nice and simple. This system should allow for quite interesting builds to be achieved one stage at a time.
Lots of people say they have a hard time soldering. Well, I wear reading glasses because my eyes are not what they used to be and my hands are fucked with arthritis, i have only 55% use of my right hand and 70% in my left hand. It is what it is and they are only going to get worse over time, so no use bitching and moaning about it, i just get on with living as much as I can.
So, soldering, here is the tip and only the tip mind you (AVE HAHA) bright white light so you can see, and extra magnification. Even as a handycapped I am working with SMD components, I just magnify things enough and use the right tools. And the tools being different shaped tweezers and a nice thick 3mm chisel tip on the soldering iron. Yes, that big chunky tip is the key to things, you want to hold as much heat in the iron as you can. Use thin solder, 0.6mm or thinner because a little dab will do ya (AVE) and with heat in the tip, you are not spending time heating things up, just dab and go, dab and go. Tack one side of the part, lay the solder over the other pad or pads and dab the iron and its done.
The parts I use go down to 0.2mm pin pitch, SOT23 and 0802 in passives. I stay away from BGA and other leadless parts, they just suck, but everything else is pretty much good to go. So don’t be afraid, just illuminate and magnify, if you can see it, you can solder it. OH and flux the fuck out of it HAHAHA, flux will make you a winner.
Well, the saying goes, 3rd time lucky. In my case it is 4th time, well 4th version of the design and 3rd time I have had boards made for this. The good thing is, it works this time. There are not masses of strays floating about anymore. They are just about all eliminated. You can see by the gain plot that its nice and linear with 0.5db loss from 1 to 30mhz. That is good enough for me. The losses are actually a little less than that, because i did not calibrate out the cable losses, but lets call it good enough for the kinds of girls I go out with.
Now its just a matter of rewriting the software to account for the changes I made and then putting it to use. Next version will have the capacitace switchable from low Z to high Z and there will be an SWR bridge and probably auto tuning. For now, i will finish this off and put it to use with some other home brew bits I have here.
I was bored yesterday so i thought i would try building an amp from these transistors I have sitting in the box. Ummm yeah I smoked it pretty hard before I even got any significant power out. I think the main thing is that I could not drive it hard enough to get it into the linear region and I might have had a bit to much bias happening. I will try again, but from what I was reading online, these transistors have a habit of wanting to detonate.
Looks pretty dont it LOL. Well it does not work. Why you may ask, well, the IO expander which was meant to be able to output 5V and 20ma per pin, could not raise the skin off a custard. 1.2V out into an open load is all i could get out of it. I do not know why, schematic is correct, the voltage is correct and the reset line is pulled high, I can read and write to the IC over I2C and turn the pins on and off, they just never get anywhere near being 5V out. Anyway, I have redesigned the board using only the pins on the micro to control the relays, having bodged some wires into it to make sure it would work.
I also have another iteration in the pipeline, were I have added some switching of the capacitance to either the input or output sides for low z and high z loads and have also added swr meter circuitry. It might be months before i have that totally ready, I am going to spend a lot more time on the layout to get it right.
Air variable cap parts arrived a couple of weeks ago now. Have had this sitting on the bench for over a week, thought i should post about it. These are the panels, i separated them by cutting the tabs off on the bandsaw. If i ever make a second iteration, I will add in some drillings to make the tabs break off.
6 plates top and bottom give a minimum capacitance of 20pf.
Fully meshed they give a maximum capacitance of 133pf. Using the parts on hand, I have enough plates to build 2 capacitors that are 60 to 400pf or there about’s, being 15 plates top and bottom. Its just a matter of spending the time assembling them. There are some changes i would make if I was to do them again, like make the rod 5mm rather than 4mm, this would make it easier to mount a knob on and things like that. There is a spring front and rear to apply resistance to the movable plates so they hold their position. Other than that, it works.