I take no credit for this project other than the changes I made for it to have an OLED display also.
I originally found this idea from a sketch by IW5EJM but can't find a link to it now. But it was improved by NT7S. There is also a similar project by Tom Igoe & Ivan Grokhotkov. And a VK (don't know callsign)
UPDATE: Try https://antrak.org.tr/blog/basit-ve-ucuz-esp-wspr-vericisi/ You may need to use Translate to see in English or other language.
Or check this Blog (Apr 2023) http://blog.marxy.org/2021/09/simple-wspr-beacon-using-si5351-and.html
Note this project while similar in some ways to the QRP_Labs "U3S" kit, all parameters are hard coded and cannot be changed while in operation, as the U3S can be.
In essence it uses an ESP8266 board along with an Si5351 board, plus a hand made low pass filter(LPF). Actually, for the LPF I AM USING IS one of the QRP-LABS LPF boards, as they are cheap and easy to obtain and come with all needed parts. I ordered 4 kits on 80, 40, 30 & 20M bands. I only plan to use 30M for now.
Initially, the project will be built onto some Proto PCB material to contain the above modules. For a display I used a 0.96" OLED display and adapted the sketch in the link above to use it. . While small, it's not anticipated that one needs to constantly monitor the WSPR Tx, but is a nice guide where you can see current status at a glance. For those inclined, it would be simple to change to say a TFT colour display, to make text larger and 'pretty' and some more details of the WSPR "progress" or state. There are various OLED displays available, the one I used is I2C interface only, (It's I2C adddress is 0x4c) but there are others which can be switched to I2C via a simple change shown on the back of module. I used the I2C only module which has 4 pins, others may have more pins but ensure that they can be used in I2C mode.
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