Homebrew PCBs

> JanK wrote:
> <snip prices>
>
> However, I got the Item 47257 (which is not
> advertised as having a computer interface),
> and discovered that there is a small slide-
> off cover which reveals 4 gold-plated edge-
> connector contacts at the edge of the
> circuit board. I don't recognise the type
> of connector this would work with. The
> contact pitch is about 60 mils or 1.5 mm.
> It should be pretty easy and safe to solder
> wires to the contacts.
> 
> Oh, are you wondering whether that interface
> actually works? :-) Well, it appears that
> the functions of the pins, from left to
> right, are:
> 
> * Ground
> 
> * A digital pulse stream, about 3 times per
> second (which is the update rate of the
> display). Bit times are about 30 us.  The
> "message" length is about 800 us. Maybe this
> is BCD. The "high" level is about 1.5V, the
> battery voltage. (Sorry, times and voltages
> are very rough - I'm using a clunky old
> scope.)
> 
> * A digital pulse stream, about 3 times/
> second. Bit times are about 5 us. Message
> length is about 800 us. Maybe this is ASCII
> or something.
> 
> * 1.55V battery voltage.
> 
> Note, the pulses continue even when the
> device turns itself off or is turned off
> with the on/off button. Also, the caliper
> doesn't lose it's zero position even after
> being "off" for many minutes.
> 
> Perhaps the calipers that are advertised
> as having a computer interface update at
> a faster rate, who knows.

www.shumatech.com/support/chinese_scales.htm

Here is a good description of how the data
on the scales/callipiers I have work.

Gotta love bookmarks on browsers.

Maybe the computer interface ones are USB
or RS232 instead of SPI ?