Schematic Questions

[PapaDonUSA]

I have several questions concerning the Si4735 schematic diagram:

1. Listed are several "jumpers". It's not clear to me as to why you are using these. Are these required? Are the jumpers meant to allow one or more of the components to be connected?
2. The circuit includes a couple of BC547 transistors that connect to the ESP and the LOUT/ROUT. What is the purpose of these? Are these required?
3. You are using both a 32.768kHz crystal and a Si5351 clock generator. Why are you using both? What is the purpose of the Si5351?
4. There is a buzzer/beeper of some kind in the circuit. What is this for? Is it needed?
5. The schematic shows a 4.7K resistor (R1) coming off of the BC557. However, your documentation indicates it should be a 2K resistor. Which is correct?
6. At the point where the SEN pin mates with the 3.3V line, you have a designation of "X063". What is this? Is there some kind of component or test point that needs to be there?
7. In a prior note, it was suggested you were working on a PCB for the circuit. Is this now available? If so, are you using SMD or through-hole components?

Thank you for sharing all of the information here. I've built a working radio using the Si4735 based on the schematic diagram by Ricardo Caratti (PU2CLR). I would like to upgrade from a 20X4 LCD to the 2.8 inch TFT display you demonstrate here. I've struggled doing this and found your information that seems clear and easily to use. I hope to use your information to upgrade!

[pe0mgb]

Hello PapaDonUSA,
I will try to answer all questions. Most of them have already been answered years ago on Facebook, but I can't find them anymore.
First, the jumpers.
Jumper JP1 is used to switch transformer T1 on or off. The transformer provides a lower antenna impedance and can be used, for example, for a loop antenna. Even with a normal 50-ohm antenna such as a dipole, the transformer will match the Si473x better. This easily makes a difference of 6 to 10 dB. Without JP1, the J4 input can be used.
Jumper JP3 must be installed when using a crystal. If an SI5351 is used, it must be removed.
Jumper JP2 switches between the crystal and the SI5351. If an SI5351 is used, JP2 must be set to the upper position and then connects the output of the SI5351 to the SI473x.

Transistors Q3 and Q4.
During the modulation switchover, the SI473X produces a loud pop. This was considered annoying and perhaps unhealthy when using larger speakers behind an amplifier. During the modulation switchover, these two transistors briefly short-circuit the audio, eliminating the pop.

Crystal and SI5351
It is possible to use either the crystal or the SI5351. The disadvantage of crystals is their small deviation, which means the radio isn't perfectly on frequency; the higher the frequency of the receiver, the greater the deviation. I have observed deviations of more than 1 kHz on 28 MHz. This deviation can be compensated for using the BFO. I reduced the problem by storing the BFO frequency for each band in memory. With an SI5351, the frequency of 32.768 kHz can be precisely adjusted. The SI5351 is quite stable at this frequency; it is sufficiently stable after 15 minutes. In the BFO mode, the SI5351 can be tuned with a good counter. If not, the SI5351 can be tuned by ear to the known frequency of a station in LSB or USB. This makes fine-tuning the SI5351 easy. The major advantage is that in single-sideband reception, using the BFO is no longer necessary, as the radio is then more or less on frequency. By pressing the rotary encoder button, the found frequency of the SI5351 is stored in memory and used continuously.

PCB
Yes the Radio Club here developed a PCB but are currently no longer shipping packages to the United States. As a non-profit organization, we cannot handle the problems associated with carrier uncertainty and the ever-changing additional import duties introduced by the White House.
Best regards,
Gert PE0MGB

[PapaDonUSA]

Gert,

Thanks for the prompt response! I greatly appreciate the information. I understand your concerns with the tariffs that the President has imposed. Hopefully this will be sorted out in time and, at the very least, will be stablized.

I like the idea of using the Si5351. I'll have to read up on it to ensure I install it correctly and make any needed adjustments. I've not used these before as I've used the regular 32.768 kHz crystal oscillator.

Thanks for adding Q3 and Q4! That is a perfect idea!

Thank you again for sharing your project. I'm looking forward to getting the 2.8" TFT LCD working. That looks so much more professional!

[PapaDonUSA]

Gert,

To clarify regarding the 327.68 kHz crystal, can I completely remove this if using the Si5351? If so, will I put the GPIO3 pin to ground, leave it open or does it connect back to the Si5351 to one of the remaining, unused pins?

[pe0mgb]

Hi Don,
If you have the crystal, you can also simply install it. As I mentioned before, you can use the jumpers to turn on either the crystal or the SI5351. Then you can try both. Even if you don't install a crystal, nothing needs to be done; just place the jumpers as described, setting them to the SI5351 position. Then everything should work. Good luck with it.
Regards,
Gert PE0MGB

[PapaDonUSA]

Hi Gert,
Thanks again for responding. To further clarify, if eliminating the 32.768kHz crystal, will the GPIO3 pin on Si4735 be left open? I assumed the reason for the jumper (JP3) was to ensure, if using the Si5351 module, to disconnect the crystal from the GPIO3 pin. If This is correct, I may likely completely eliminate the crystal. I've ordered the Si5351 module. It should be here in a few days.

As a second question, you have a 4.7K resistor, a BC547 transistor and a "BUZZER" connected to GPIO32. What is the purpose of this? Can this be completely eliminated? If it is needed, can you provide the actual component I need to order?

Again, thank you greatly for your help. I'm really excited about building this version!

[pe0mgb]

Hello Don,
Sorry, I missed your email. I found it while cleaning out my mailbox.
You can simply leave out the crystal along with jumper jp3. The buzzer will beep when you press a key on the screen. It confirms a valid key press. Without the buzzer, everything works fine. Aliexpress sells the TMB12A05. !0 pieces for less than a dollar.
Regards, Gert

[PapaDonUSA]

Hello Gert,

I hope all is well with you and your family!

I've completed the PCB I had made using your schematic diagram. Now I'm attempting to load the sketch "SI4735_2.8_TFT_SI5351_V3.5.ino" (I assume this is the most recent version) onto my ESP32-DEVKITC-D2. Unfortunately I've run into errors in compiling. The first two errors are related to

ledcSetup(LedChannelforTFT, LedFreq, LedResol);
ledcAttachPin(Display_Led, LedChannelforTFT);

The error message says, these two were "not declared in this scope;." I've gone back and written in "#define ledcSetup" and "#define ledcAttachPin" at the top. This seems to eliminate the error. However I'm unsure if this is the correct thing to do (please note that my programming skills in Arduino are minimal).

The next error is related to "tft.setTouch(calData);"(line 991). The error message says, " 'class TFT_eSPI' has no member named 'setTouch'." I'm unsure where the error is and have no idea how to fix this. I did ensure I have the TFT_eSPI version from https://github.com/Bodmer/TFT_eSPI as required.

Can you advise how I might fix these errors?

If related to the errors, I did make a couple of changes to the sketch:

1. "IhaveLiPoLoadbar": I have removed this from the sketch as I am not using a battery of any kind. I'm hard-wiring this to a PSU.
2. "NandSAmericanbandplan": I have opted to use this version as I live in the United States.

Again, thanks for all the help. I'm looking forward to getting this to work. Hopefully you can help me through these error messages.

Best Wishes,
Don Wilson
Jasper, Georgia USA

[PapaDonUSA]

Hello Gert,

As an adendum to my last question, I was able to clear all of the error messages and was able to upload the sketch. My only concern is regarding the additions of "#define ledcSetup" and "#define ledcAttachPin". Although adding these two lines allowed the sketch to compile and load, I'm unsure as to why it wouldn't load without them. Any thoughts as to why?

Again, thank you for all of your assistance.

Best Wishes,
Don Wilson
Jasper, Georgia USA