Arduino Leonardo Serial Input

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Re: Arduino Leonardo Serial Input

Postby Osgeld » January 9th, 2013, 9:18 pm

yes you will need to power the device to check voltage levels, and personally I bet if you pop it open you could find a max232 like circuit on board keeping a computer from blowing its 5 volt circuitry up.

@ UAirLtd its not all silly, and you can trace it back to telegraphs if you really wanted to dig in deep, its just archaic
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Re: Arduino Leonardo Serial Input

Postby DFTBA4ever » January 10th, 2013, 7:53 am

How do we know it doesn't draw voltage from the RS232 and data on the PS2?
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Re: Arduino Leonardo Serial Input

Postby k-ww » January 10th, 2013, 8:39 am

Except for some old serial mice, it wasn't practical to pull power from the RS232 pins,
and there are no power pins defined in the RS232 spec, while the PS2 connections
have +5 & gnd on them, with enough current [100ma?] to power devices.

If you need a quick and dirty RS232 to ttl converter, you will need an NPN transistor and
two resistors - say 47K and 10K. Connect the emitter of the transistor to gnd, the collector
to a 10K resistor who's other side is connected to +5 / +3.3V [whatever your micro's power is],
and the base to the 47K resistor, and the other end of the 47K resistor to the output pin of
the GPS unit [depends on if it is a 9 or 25 pin connector]. The junction of the 10K and the
transitor is the micro level output signal for your circuitry. Don't forget a ground connection
between the GPS and your micro also.

Please test your GPS unit by hooking it up to a PC [with RS232] and using hyperterminal
to look at the data stream. Start with 2400 baud as the speed and go up.
This way you will know what the data looks like.

If your computer dosn't have a serial port, do you have a rs232-usb converter?
Hyperterminal works with those also.

On a 9 pin cRS232 connector, pin 5 is gnd, and either pin 2 or 3 is the output signal
[look with a meter for a negaive voltage on the pin.
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Re: Arduino Leonardo Serial Input

Postby UAirLtd » January 10th, 2013, 9:46 pm

Osgeld wrote:@ UAirLtd its not all silly, and you can trace it back to telegraphs if you really wanted to dig in deep, its just archaic


I didn't mean "silly" as in "that was a silly design decision". I said "all silly", like sort of a childish way of saying "all strange and unusual".

DFTBA4ever wrote:How do we know it doesn't draw voltage from the RS232 and data on the PS2?


It's unusual for things to be powered off RS232 these days, you can kind of get away with it for low-power things, but definitely not for a GPS receiver. RS232 lines aren't designed to supply much current, and drawing current from it risks damage if you exceed the supply limits.

[quote="Osgeld"]
I bet if you pop it open you could find a max232 like circuit on board keeping a computer from blowing its 5 volt circuitry up.[\quote]

I agree, this is highly likely, if you do find an RS232 level converter circuit, you'd probably be able to trace the signals back to the original 5V TTL serial data lines that you could feasibly directly connect to an Arduino, bypassing all this need to use level converters.
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