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sivaji , 11-19-2024, 05:05 AM

I have the ST3020 servo and Bus Servo Adapter (A). Using UART communication with ESP32, which was working perfectly. The dimension of the Bus Servo Adapter (A) was not suitable for our application. I found a schematic on the Waveshare website, and I have made a circuit out of it, which is having some issues with communication. I have attached my observation, circuit, and waveform herewith.
I need your support to find what I missed...

Robert Feranec , 11-19-2024, 06:17 PM

please, can you explain more about what is connected to the connectors? Just would like to understand better the schematic

QDrives , 11-19-2024, 08:52 PM

What does this circuit do? TxEn is driving your output enable too.
And I would not use CH343 but either FTDI or Prolific. I had some bad experience with a CH343 device.

sivaji , 11-20-2024, 10:20 AM

This is a serial bus servo driver circuit designed to control a servo motor using the TTL control method. The connector (J1) includes TX, RX, and GND pins, which will connect to the corresponding TX, RX, and GND pins on the Raspberry Pi. The data pin on connector (J4) will be connected to the DATA input of the servo motor. Additionally, connector (J2) provides the power supply for the circuit, supplying 3.3V and GND.

QDrives , 11-20-2024, 09:09 PM

That does not explain the reason for the circuit I shown from your (pdf) schematic.
If I think what you may want to do, why not use the SN74LVC1G07 directly instead?
Or better, have a 'drive enable' pin like you would have with RS485.

sivaji , 11-21-2024, 05:34 AM

sivaji , 11-21-2024, 05:36 AM

Please have a look the attached file for explanation

QDrives , 11-21-2024, 09:49 PM

"*There is no communication is happening.*" -- Communication here I assume is both directions?
Do you get outgoing signals?
Do you get something back?
Is the Altium schematic your design? If so, how/where is the U1TXD and U1RXD connected?

sivaji , 11-25-2024, 10:24 AM

1. Communication here, I assume is both directions?
**Yes, where TX and RX are combined into a single line called data. Neither two way nor one way is responding.**
2. Do you get outgoing signals?
**Yes, outgoing signal is what we are triggering. This signal itself is not matching with the serial bus servo adapter.**
3. Do you get something back?
**Yes. When I have tested with a derived board connected to a servo, the signal comes back with the same differences. **
4. Is the Altium schematic your design?
**No, I am using Kicad version 8.0. **
5. If so, how/where is the U1TXD and U1RXD connected?
**The U1TXD and U1RXD are terminated to Raspberry Pi 3B+ GPIO14(TX) and GPIO15(RX). **

Kindly refer to the "ServoDriverCircuitIssue.pdf" in the earlier message.

Thank you in advance!!!

QDrives , 11-25-2024, 07:38 PM

The scope statistics show for the one signal 80mV for Vbase and the other 600mV. Vtop in both cases is 3.28V
However, the signals shown are equal below and at the top different.
Which is correct?

sivaji , 11-26-2024, 12:22 PM

From the scope images, CH1 (yellow) is the Waveshare servo adapter board signal, and CH2 (purple) is the derived circuit board signal. among these, CH1 (Yellow) is the correct signal, which is working with servo motor (ST3020)
Thank you in advance!

QDrives , 11-26-2024, 04:13 PM

What about the voltages?

sivaji , 12-07-2024, 01:12 AM

Hello,I have redo the PCB again and found that working stable. Appreciate your continuous support. Thank you so much.