Re: Low cost GPS receiver?

[Paul Fertser]

Hi,

On Thu, Mar 30, 2023 at 12:02:31AM -0700, Chris Kuethe wrote:
> I haven't used a serial device in a long time that actually required EIA232
> signaling. Everything I've used in the last decade was 5v or 3v.

15 years ago when desktop motherboards still had DE9 connectors for
RS-232 I was testing simple AVR ISP flashing methods, and I confirm
the motherboards were accepting 5 V as if it was logical 0, and 0 V as
if it was some negative voltage meaning logical 1. So bidirectional
communication with 5 V-powered AVR MCU was possible without any active
devices, just resistors and clamping zeners. With inverted levels of
course, as UART logical one is usually at +Vcc while RS-232 logical
one is some negative voltage.

BTW, common (back then) MAX232 RS-232 PHY was meant to be used with 5V
Vcc and so it was doubling it to produce -10 V / +10 V
signals. MAX2323 was for 3.3 V power, so the resulting waveforms were
-6.6 V / + 6.6 V. I do not remember reading about any compatibility
issues with either.

> I'm betting that a pc with a 5v level shifter with work just fine
> with a GPS. 

Shifter and inverter.

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