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tlfong01
tlfong01
2:25 AM
Ah, this is useful to me: "From the tests I did, I found it is much less than 1ms".
Yes, I agree with the following: "Nobody expect the chat to be a precise document. (IMO) is fine to have typos, and errors, (I am not even sure many people will read this)"
And now I think that readers following this chat should automatically filter the typos as he read along. As I said earlier, I might try to make a summary after each milestone, and also brief project report on completion of project.
BTW, I googled further but still have not found useful to guide me where to go next on serial bus servos. This is another abandoned project: GigaBrain Dynamixel and LX-16A Project - rpi.org.forums 2018sep19
https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=196187
https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=196187&p=1334212&hilit=lx+16a#p1367598
https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=196187&p=1334212&hilit=lx+16a#p1336280
I am also updating my knowledge on logical level shifters. Here is an updated of the catalogs: (1) Logical Level Shifter Catalog - AdaFruit
https://www.adafruit.com/category/864

(2) Logic Level Converter Catalog - SparkFun
https://www.sparkfun.com/categories/361
It is too late for me to update (2) to following: (2) Logic Level Converter Catalog - SparkFun (***I always forgot that opto-isolaters are also level shifters***)
https://www.sparkfun.com/categories/361
 
 
5 hours later…
tlfong01
tlfong01
8:03 AM
Yes, my test confirms your much less than 1ms is about 200us
The output has a little problem. The TXS0104's 10k Or'ed 10k (Or'ed with LX-827 input) seems not strong enough, with the result the output could not be pulled down to a clear cut zero. I tried to parallel 4k7 to make the pull up stronger, but it seems not making any difference. Anyway, Rpi at the 3V3 side seeem to read the data OK.
I forgot to give a title to the above scope screen capture.
I also now understand why you said that each LewanSoul byte is 10 bits, beginning with "10". More precisely, the beginning "10" should be "stop bit/idle high bit/level ("1") and "start bit" ("0").
Anyway, the TXS0104 circuit seems working, though not perfectly. So I will move on to tidy up my quick and dirty python program and show a complete listing here, perhaps some time after afternoon tea/jogging/supper. Cheers.
 
 
5 hours later…
tlfong01
tlfong01
1:26 PM
I forgot that the TXS0204 5V side TxD ORed with RxD and LX-824 is shifted down to 3V3 and at 3V3 side RxD read by Rpi is between 1V (Low) and 3.2V (High) and therefore acceptable to Rpi.
 
tlfong01
tlfong01
1:47 PM
And this is the complete listing of the program to test the TXS0104 LX-824TV interface circuit. 
# srv_util_01_v153.py
# LX-824HV Testing v1.0  tlfong01 2020sep15hkt2133

# Contents

# Serial UART LoopBack Program v0.62 (Minimal)
# Serial UART LoopBack Program v0.98 (Multiple ports USB and on board UYART Ports)
# HiWonder serial bus servo LX-824HV LewanSoul command testing (2020sep15)

# Serial UART LoopBack Program v0.99 - penzu.com/p/f2cb232e
# serial_loopback_test_v062.py tlfong01 2020jun03hkt1447
# Rpi4B buster (r2020feb13), python 3.7.3 (r2019dec20), thonny v3.2.7 (r2020jan22)
The above program follows the recommendation style of StackOverflow - MCVE (Minimal, Comprehensive, Verifiable Example). Or CPR (Copy-Paste-Run) No external library is required to run it.
 
 
1 hour later…
tlfong01
tlfong01
3:14 PM
I am going to write some more python programs to control the LewanSoul serial bus servo. I google a couple of forums and found quite a lot of discussions on Dynamixel and almost nothing on LewanSoul servos.
Luckily we have the following two references: (1) LewanSoul Bus Servo Communication Protocol User Guide. (2) lewansoul_lx16a_terminal.py, Maxim Kulkin (maximkulkin), GitHub 2019feb27. One bad thing is that all things I found are based on LX-16A, nothing about LX-224HV and LX-824HV. Anyway, I think we have enough references to move on.
I found the following two EE SE forum discussions on serial bus servo Dynamixel, but I found them not very useful. (3) Single wire two-way serial communication - hardware configuration （Dynamixel XL-320）- EESE 2015aug05
https://electronics.stackexchange.com/questions/183410/single-wire-two-way-serial-communication-hardware-configuration

(4) How can I make a half-duplex UART to TTL converter for communicating to a servo (Dynamixel AX-12A) with a HC04 and a HC126? - EESE 2020jul20
https://electronics.stackexchange.com/questions/511349/how-can-i-make-a-half-duplex-uart-to-ttl-converter-for-co…
 

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