I just inherited a old style stamps.com digital scale. I am currently
doing a lot of shipping and am looking for a way to connect the scale
to my computer.
The scale has a mini stereo plug on the back for a serial connection
(yes, it IS for a serial connection and not the power adaptor) however
I do not have the cable. It would be easy enough to make if I had a
set of pinouts for it. There are no manufactures names or model
numbers listed on the scale itself. Images of the scale and connectors
are available at: http://www.isthatdamngood.com/google/stampsscale.html
A set of pinouts for the cable for this scale would be the best answer
to my problem. Second to that would be a location to order just the
cable.
Seantobin,
Great photos! They're really all the information you need. The black
wire from the stereo adapter on the scale runs to the ground plane of
the circuit board, so it has to be ground. The white wire runs to what
looks like pin 14 of what might just be a MAX232A TTL-to-RS232
converter (this is a guess, but it looks like pin 15 goes to ground
and pin 16 goes to +5V, so it is a possibility - you should give us a
shot of the top of the chip for positive identification).
Here is the pinout:
Scale end: Shield is ground (black cable)
Tip is TXD (white cable)
There is a remote possibility that Ring, rather than tip is your TXD,
but you can find out very quickly using a voltmeter or continuity
tester by plugging in the stereo plug you are going to use to make the
cable and testing connectivity between the white wire and the Tip. You
may also want to confirm that the black wire goes to shield (though
it is quite obvious from your pictures that it does). If you do not
have the ability to test this, you should probably abandon the idea of
making a cable yourself. Make sure the scale is turned off when you do
this and that you do not short the stereo plug or introduce static,
especially to the white wire.
Explanation of terms: Tip is (obviously) the contact at the pointy end
of the stereo connector. Ring is the small ring adjacent to the Tip.
Shield is the long connector furthest away from the tip.
Computer end, 9-pin serial:
Pin 2 RX (Receive Data)
Pin 5 GND (Signal Ground)
Computer end, 25-pin serial:
Pin 3 RX (Receive Data)
Pin 7 GND (Signal Ground)
You should connect Tip (TXD) on the stereo plug to RX on the serial
port, and Shield (GND) on the stereo plug to GND on the serial port.
Please take care to ensure that you are connecting to the correct
pins. You are using a connector for the end of your cable, so you have
to reverse any diagrams of pin numbers that show the PC's ports,
rather than the connector's ports.
Try these for diagrams:
http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm#db9
http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm#db25
A 2-wire serial communications setup allows data to flow one-way from
the scale to the computer with no flow control. Figuring out what
speed the scale is sending data is fairly easy: play with the settings
in the communications software until the data makes sense.
Here is an application designed to work with a 2-wire serial connection:
http://www.magsys.co.uk/comcap/
With TTL or RS232 level signals, it is actually very difficult to
damage either your PC or the scale by wiring it wrong, but Murphy's
law applies. Do take care to check all connections for appropriateness
or shorts before connecting the cable and avoid static (on general
principles). I'm pretty sure about this advice, and I would have no
hesitation to do this myself, but beware that you could destroy your
computer and scale, blah, blah, blah.
Best Regards,
Alan Kali CDM-550T::
File Format: PDF/Adobe Acrobat - View as HTMLConnector Pinouts. Rev. 1.3. 5–3. 5.4. Auxiliary Serial Connector - HE1402 vertical scale of 1 or 2 dB/division, and use video filtering and/or video
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Stamps.com digital scale serial pinout