Serial Output with External Power Supply

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stylefungus

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I have an application that works fine on a Teensy 3.6 when powered from a PC. This outputs serial data using converters to multiple devices. If I use an external phone charger, the application runs but serial does not work. It is definitely a grounding problem because if I touch a wire from the outside shield of the usb connector to the outside shield of the PC usb cable it works. So I know I am doing something newbie-ish and improper. How do I power and ground this properly to run stand alone and if anyone has a link to a proper power supply I would greatly appreciate it.

Thanks

The man from Originalcow.com
Grass Fed Local Beef
 
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again hard to know what is going on without pictures and code.

Also hard to understand exactly your issue. Serial does not work? Are you talking about one of the hardware Serial ports (Serial1-6) or are you talking about the USB Serial (Serial)?

Again don't know how these are wired, but maybe your charger does not have a proper ground or there is no common ground run between your Teensy and your devices.

Or maybe the voltages are not correct?
 
All the devices you have connected must share a common ground otherwise the serial port will not communicate. Between all devices the cable should have 3 conductors, transmit, receive and ground. The ground must be connected to the ground of the devices on both ends of the cable.
 
KurtE said:
again hard to know what is going on without pictures and code.

Also hard to understand exactly your issue. Serial does not work? Are you talking about one of the hardware Serial ports (Serial1-6) or are you talking about the USB Serial (Serial)?

Again don't know how these are wired, but maybe your charger does not have a proper ground or there is no common ground run between your Teensy and your devices.

Or maybe the voltages are not correct?
Click to expand...

OK Gotcha . So what I have is ...I am connecting a TTL Converter to Teensy Pin 7 (RX3) Pin 8 (TX3), VCC to 3.3V, and Gnd to Gnd

I print to a serial Epson Printer. There are no issues with the communications. I can send data and it prints great so long as I am on the PC USB as a power supply.

Once I connect a different power supply to the Micro USB port, the program runs only There is no data transfer. If I ground the unit to earth ground while powering from the power supply, the communication works once again. So my question is what is the best way to power the unit with proper ground as there is none when using a 2 prong usb cell phone charger
 
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