The normal MAX232 type level shifters include an inverter.

So even if the voltage levels work without a level shifter, the signal will
be upside down.

--
These are my opinions, not necessarily my employer's.  I hate spam.

Hal Murray wrote:

To play safe, if one isnt sure that an inverter is required or not an
exclusive OR can be used so that the signal can be inverted or not as
required.

Bruce

Quoth Hal Murray at 2008-03-07 19:59...

I'm building my test board with a hex inverter that I'm actually using
to buffer the 1PPS signal.  I've got spare gates on there so will build
the board with jumpers so that I can invert or not invert (that is the
question ;-))

As I'm working with two different types of GPS module, and may have
others, my development board will have a lot of jumpers so that I can
actually patch together something that works before I build the final
boards - something that I feel necessary as I always seem to get my
TX/RX mixed up!

Just to clarify - I don't tend to use breadboards as they tend to take
longer to debug than making a PCB.  When PCBs are concerned, I tend to
use SMDs wherever possible until such time as I find a way of making
holes that a) doesn't break my drill every other hole and b) actually
lines things up properly.  (A CNC XY drill rig would be really nice -
better buy a lottery ticket.)

Cheers

M

--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
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The inverter is required because the Motorola GPS receiver uses TTL and
the PC serial port uses RS232.

RS232 uses a positive voltage of +3 to +25 volts to indicate a logic
zero, and a negative voltage of -3 to -25 volts to indicate a logic one.

Brian KD4FM

Bruce Griffiths wrote:

Attached is a interface for an Oncore VP receiver.  You will have to
check - I believe the GT and UT use the same connections as the VP.

Brian Kirby wrote:

Quoth Brian Kirby at 2008-03-08 14:46...

Thanks Brian - that's pretty close to what I've come up with apart from
the fact that I'm putting isolation (TI ISO7231) between the receiver
and the rest of the circuit and the receiver is powered by a MeanWell
high-isolation DC/DC convertor.  And I've got mine running right to left ;-)

I've got a something very similar drawn up for my Trimble modules except
that the isolation and level conversion is x2, for the two serial ports.

Cheers

M

--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy

For isolation of digital signals such as RS-232 (before level translation),
it's hard to find something more amazing than the Analog Device ADuM5241

http://www.analog.com/en/prod/0,2877,ADUM5241,00.html

It's an SO-8 device, with two digital channels, isolated to 2500V (!) and a
built-in power converter that delivers 5V @ 10mA.
All in an SO-8 package. The power converter runs at 300 MHz.
But wait, it costs <$3 in 1,000 pcs quantity.
They have other options in the same series, with more channels (in a larger
package).

After seeing that, the LTC 1535 from Linear Technology, which would be
pretty amazing in it's own right, looks pretty dull:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1007,C1017,P1746

Didier KO4BB

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