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Wednesday, 25 March 2020


I've been fiddling some more since the Linear we built a little while ago here.

Some musings below on power meters, directional couplers and measuing RF power:

I hope you are all keeping safe - its very scary out there.

Wednesday, 11 March 2020

TFTs and Blue Pills - Are you sure?


I've been using the STM32 processor (STM32F103 for those playing along at home) based "Blue Pill" board. This board is compatible with the Arduino IDE and I have been using it with the ILI9341 super duper TFT display module.

This is the board in question:

The STM32 board support can be added easily to the Arduino IDE, just add this line:

to the preferences screen:

Once you have done that you can then install the STM32 cores from the board manager:

I wrote some very simple code to generate Pi using floating point maths:

Set to calculate 100,000 itterations, the good old Arduino Nano ran this code in 29.60099983215332031250 seconds. This Blue Pill board runs the same calculation in 3.07200002670288085937 seconds. Cooking!

Here' how I have wired the test up for the TFT:

I have used the library called "TFT_eSPI" which is here. In the more modern Arduino IDE you just search for it and install from the library manager.

Once you have done that you need to make a couple of edits to the "User_Setup" file which you can find in the libray directory.

Here's mod 1:

and this is mod 2 - please use pins of your choice here:

Once you have done that all should be well!

Please note that this library and config only works with the Arduino STM32 cores and the HID bootloader.....

Friday, 14 February 2020

Making a 10W "QRP" ish linear

I've started to design some software that will control a low power linear amplifier.

I plan to use the 10W Amp from QRPLabs as the main component - I can't make one for the price they sell these kits, so thats on order.

In the meantime, I've been designing some software to control the output switching, and calculate the forward and reflected power and SWR:

Initial software design is included for the STM32 "blue pill" baord.

The software can be downloaded here.

The pinoput for the STM32 board is here.

The schematic for the RF sence using AD8307 is here.

You can purchase a STM32 board here.

The TFT display with touchscreen functionality is here:

More to follow on this topic.

Here's part 2 where I look at the Low Pass Filters and the Log Amps to take accurate power readings in software:

The finsl control software is here.

The simple software based sequencer software is here.

The schematic for the transistor switches I used in the sequencer is here.

The wiring layout for the STM32 is here.

The AD8307 schematic is here.

Sunday, 2 February 2020

A STM32 Processor - really?


In my never ending desire to fiddle with Microprocessors and/or Micro controllers, I found these boards on my local Amazon with prime next day delivery:

They are called a "Blue Pill" for some reason?!?!? The boards I ordered are these. At the time of writing I could buy 5 of these boards for £15 GBP delivered.

You can use them directly with an external USB -> Serial converter, but you can also upload a bootloader and make the on-board USB port work successfully.

I followed the instructions here:

the speed of these processors is excellent and when used in conjunction with the ILI9342 displays I have been using recently they work very well indeed.

You can see an example of the processor in action in my latest musings on the BITX:

All very impressive and I still fail to believe how inexpensive these MCUs are.

** UPDATE **

There is an alternative bootloader (its much smaller) available for this board now, you can find instructions for using it below. This uses the HID method for uploading:

Back to the BITX


I wanted to do a simple (ish) construction project for my YouTube channel and decided a BITX would be just the ticket.

If you like what I am doing please subscribe to my channel and give me some support.

Thanks muchness!

** UPDATE **

Following the issues I noted in the video on balancing the Balanced Modulator, I have added some capacitance either side as highlighted in this image:

By careful adjustment of the balance pot and the trimmer I have now got excellent carrier supression:

much better, dont you think?

Sunday, 19 January 2020

Spectrum Analysis


I've been messing about recently with some inexpensive alternatives to a Spectrum Analyser. I find my Rigol DS-815 one of the best investments I've ever made, it represents excellent value for money. However, its still an expensive purchase and I wondered if the inexpensive alternatives were any good.

First off, I tried one of these that you can source on all good auction sites, here is a link to the device on Amazon:

Without a box

and also:

With a box (if you are posh like me)

They look like the image above and represent exceptional value for money - you couldn't purchase the bits for the price.

Here's my evaluation of the device:

Second I tried an SDRPlay and associated software as a Spectrum Analyser:

Next will be a Red Pitaya... so watch this space.

Sunday, 12 January 2020

STM STM32F103RC8T6 - really?


On popular auction sites you can find these boards for less than 2 GBP delivered:

They contain (on the underside) a STM32F103RC8T6 processor from ST Microelectronics. Looking at my musings from here, these boards will support the necessary double precision maths and also have the SPI interface needed for frequency synthesyser interfacing - amazing!

These will work with the Arduino IDE with a very small amount of effort.

Assuming you already have the Arduino IDE installed (if not go get it), the steps are:

  1. Go to the Tools -> Boards -> Board Manager and install the Arduino SAM boards (Cortex-M3)
  2. Download the STM32 support package from here.
  3. Unzip the download to create the Arduino_STM32 folder
  4. Copy the Arduino_STM32 folder to My Documents/Arduino/hardware (Note: if the hardware folder doesn't exist you will need to create it).
  5. Navigate to My Documents/Arduino/hardware/drivers/win and run the install_drivers.bat file - right click and run as Administrator
  6. Restart (or start) the Arduino IDE and select "Maple Mini" as your board, "Original" as your bootloader
  7. Attach the board to the PC with a USB cable, you should see a "Maple DFU" device under "libusb-win32 devices"
You could then try this sketch and upload it to the device; please note that at this point you don't have a COM port for the board - it is using the bootloader via the DFU device instead.

Once the sketch is loaded you will then see a COM port "Mapel Serial" which you can now also select in the Arduino IDE tools -> Port.

I've connected my board to my SV1AFN ADF4351 board as follows:

STM32F103RC8T6 Pin 7 -> SPILEA (pin 3)
STM32F103RC8T6  Pin 6 -> SPICLK (pin 1)
STM32F103RC8T6  Pin 4 -> MOSI (pin 4)
STM32F103RC8T6 VCC -> 3V3 (pin 7)
STM32F103RC8T6  GND -> GND (pin 5)

and have run this sketch - seems to work just fine.

I then ran this sketch - and followed the instructions in the Serial Monitor to upgrade the bootloader - once I'd done that I then needed to select Tools -> Bootloader Version -> 2.0 for any future comms with the board.