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Topic: Is it possible to split the hardware serial port on a UNO? (Read 1 time) previous topic - next topic

satoer

Is it possible to use the hardware serial input for a GPS sensor as well as USB serial monitoring serial output?
I have a gps sensor spitting out information at 38400 baud and SoftwareSerial the arduino Uno can't keep it up. So I thought I try the hardware ports. But wat I've been reading about this port it is sharing with the USB for monitoring. Is it possible to split this port so I can use the input for monitoring the gps and the output to the USB, for monitoring on the computer?

Coding Badly

Is it possible to use the hardware serial input for a GPS sensor as well as USB serial monitoring serial output?


Depends on the GPS.  It has to be able to sink 5 volts / 1000 ohms = 5 milliamps on its transmit line.  (use 10 mA as the condition so you have a safety margin)

If the GPS can then what you want to do should work.  Everything has to be configured for 38400 baud and you cannot transmit data from the PC to the Uno.

satoer

THe GPS outputs a 3,3V ttl signal. So that's a problem? It's above the 60% for the Arduino to recognize it as "High".

Coding Badly


Paul Stoffregen did a nice analysis proving that a 3.3 voltage device connected to a 5 volt Arduino would be OK.  But the analysis was for I2C using the internal ~20K ohm pullup resistors.  I assume what is essentially a 1K ohm pullup resistor on a 3.3 volt TTL-serial line would cause a problem but I honestly do not know.

The current concern is about the electrical side so I'll move this topic to General Electronics.  Hopefully someone with more knowledge than I (which doesn't take much  ;)) will offer help.

PeterH


Is it possible to use the hardware serial input for a GPS sensor as well as USB serial monitoring serial output?
I have a gps sensor spitting out information at 38400 baud and SoftwareSerial the arduino Uno can't keep it up. So I thought I try the hardware ports. But wat I've been reading about this port it is sharing with the USB for monitoring. Is it possible to split this port so I can use the input for monitoring the gps and the output to the USB, for monitoring on the computer?



As I understand it, the hardware serial pins are physically wired up to the USB driver chip. Unless you were willing to cut tracks, I suspect you'll find that having two sources trying to drive the same input line won't work.

Coding Badly

As I understand it, the hardware serial pins are physically wired up to the USB driver chip.


...through a 1K series resistor.  As long as the USB side is idle (PC not transmitting), the circuit is essentially a line with a 1K pullup resistor to 5 volts capable of sourcing up to 20 milliamps.

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