Re: RS232 convertor - Why?
- From: NMEA0183 <me@xxxxxxxxxxx>
- Date: Sun, 03 Dec 2006 10:19:24 +0800
On Sun, 3 Dec 2006 00:35:33 +0100, "petrus bitbyter"
<pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx> wrote:
<crispin.proctor@xxxxxxxxx> schreef in bericht
news:1165096222.005283.227770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi All,
I used to enjoy electronics as a hobby many years ago but sort of left
it behind in the last 10 years.. :(
I have now rekindled the hobby by building myself a GPS attachment for
my camera (Nikon D200)
Soldering skills are not what they used to be but and a few attempts
later and some trips back to the shop for more veroboard and
components, I got it working.
To the question:
The GPS device pumps out serial data. Fine. Happy with that.
The Nikon accepts serial data. Fine.
Why is it that all the circuit diagrams I find on the net stay I need a
MAX232 IC in between? Are the levels different? If so, which is higher?
Would sticking the TX from the GPS straight into the camera cause a
loss of that ever important smoke (Electronic components work on smoke;
once it escapes, they work no more.)
Compliments of a few sites I have found on the net, I built the RS232
circuit and the camera detected the GPS data and all is well.
My question stems from the fact that I have this lovely little GPS
receive all with SMT and a smart little smoked box. Now I have to have
an ugly veroboard black box attached as well. (or stick everything
thing into a larger box)
TIA for any help...
There are lots of tastes in serial data transfer. The RS232 as used by the
COM-ports in PCs are most commonly known by the general public. The signal
level vary from +/-5V to +/-12V or something in between. Which is well
according to the specifications. The serial data from cameras is at TTL
level so 0-5V (or 3.3V these days.) AFAIK the Nikon D200 uses 0-5V. So the
point is: What's on the GPS side? If it's true RS232, you'd frie the serial
interface of your camera when connecting directly. If it's also TTL the
should have the same levels or you may damage your equipment as well.
Apparently your GPS speaks RS232 as it is unlikely (to say the least) you to
have a working connection by now.
NMEA I/O from a GPS receiver is TTL swing but opposite polarity to true RS232.
So apart from the level shifting - which in MANY cases is not required - the
inversion in a MAX 232 (et al) is the key ingredient in most of these circuits.
Regardless of actual signal levels, I'd be betting that the camera has true
RS232 polarity at its serial port and can direct connect to a PC's com port.
The odd-man-out in these schemes is the GPS receiver. The NMEA signalling
system was designed to directly interface (and multi-drop) to other marine
electronic devices such as autopilots, NOT personal computers. Some later GPS
receivers have USB output to satisfy the market for direct-PC-connection.
.
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