RX/TX serial port garbage dependent on voltage on Betz board.

[tfabris]

Pre-conditions:

• BlueGigaEmpeg board assembly is connected to both the the WT32i chip and to the Arduino.
• Using the BetzTechnik WT32i breakout board connected to the BlueGigaEmpeg board.
• Monitoring the debug console of the Arduino with the Arduino Serial Monitor program.

Symptom:

• Some of the strings of communication data from the Betz board are interspersed with occasional garbage characters.
• This causes some intermittent command/response pairs between the BlueGigaEmpeg code and the WT32i to fail.
• This is not the same thing as an RS-232 buffer overflow, I can tell what those look like now. This is something different. This is characters being read, but they are coming out of the WT32i serial ports every once in a while as garbage characters.

Repro:

• Connect to Arduino with Serial Monitor.
• In the Serial Monitor, repeatedly type the following command and press ENTER after each one: set set set set (etc.)
• Expected: You should always get a perfect screen full of perfect uncorrupted data.
• Actual: Sometimes the characters are incorrect, such as question mark characters or wrong characters. Look closely.

Conditions in which it repros:

• JP4 on Betz board is cut so that the UART is not powered.
• Arduino cable is connected to Arduino and computer and you are monitoring with Serial monitor (so Arduino is getting 5v from its USB port).
• BlueGigaEmpeg is also fully connected to the empeg docking sled Tuner/Power/I2S plug.
• Therefore BlueGigaEmpeg is also getting its power from the Pololu 5v power supply.

Conditions in which it does NOT repro:

• Using the BlueGiga dev board instead of the Betz board.
• OR...
• JP4 on Betz board is NOT cut and so the UART is powered (also have to locate and cut the traces for the RX/TX lines between the UART and WT32i for this arrangement to work).
• OR...
• The empeg is not connected to the BlueGigaEmpeg module and so it is not receiving power from the Pololu power supply (power is only coming from the Arduino USB port).

Unknown condition:

• Powered only from the empeg+Pololu, with no USB cable connected to the Arduino at all. Since I cannot directly observe the bug unless I'm using that cable, I have no idea if this fixes the issue or not. The repro is intermittent and the outwardly noticeable problems caused by this are even more intermittent. So I don't know if having a "single power source" is the correct solution or not.

[tfabris]

Possible: Voltage from Betz TX to Arduino RX might be too small. Try a pullup resistor as suggested by Mark Lord on EmpegBBS.

[tfabris]

2k pullup resistor on arduino RX2 line seems to work. Closing issue. Reopen if you see more problems.

[tfabris]

Later, removed the pullup resistor because we converted the Betz board to 3.3v and it worked to fix the garbage.