Homebrew PCBs

Some items of possible interest to PCB and CNC homebrewers:

12 inch paper shear with 6mm thick blade, is sturdy enough to cut 1/16
thick FR4. On sale in my local store for $12.99. On line catalog shows
$19.99. Item number 09805.

Several digital calipers are on sale. Item 47257 is a 6 inch digital
caliper, .0005 inch resolution, .001 inch accuracy, $15.99. Item 47261
is a 12 inch version, on sale for $34.99 in the on line catalog.

Item 93941 is an 8 inch caliper with "extra large LCD readout". Also
has "Built-in computer interface port". On sale in the on line catalog
for $29.95. In my local store the 6 inch version was on sale for
$19.99. There is also a 12 inch version, not on sale, for $64.99.

Any of these calipers should be good for direct readouts of XY tables
on drilling and milling machines, etc. I didn't figure out while I was
in the store where the computer interface was on the calipers that
have them. It's not shown in the instructions, and the calipers don't
come with an interface cable.

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.

Cheers,
- Jan

> 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 ?

--- In Homebrew_PCBs@yahoogroups.com, "Jan Kok" <jan.kok.5y@...> 
wrote:
> 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.
> 

Neither the 30 uS nor the 5 uS time corresponds to a 'normal' 
serial baud rate.

The 30 uS bit rate falls part way between 19200 (52 uS) and 38400 
(26 uS). Does the pattern of that pulse stream change as the caliper 
is moved? Any changes would indicate that it's the measurement data 
being sent to the display. (The changes may not appear to make much 
sense since they could represent display segment changes rather than 
the actual numeric values.)

Is the 5 uS bit stream a toggling clock that runs throughout 
the 800 uS period? If so, that sounds to me like it's a clock for 
the display data being sent in the 30 uS stream.


Regards, Bob

>> JanK wrote: 
>> <snip>
>> * 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.
>> <snip>

> Bob wrote:
> 
> Neither the 30 uS nor the 5 uS time
> corresponds to a 'normal' serial baud
> rate.

There is no "baud rate" it is SPI

(lets play master and servant)

> <snip>
> Is the 5 uS bit stream a toggling clock
> that runs throughout the 800 uS period?
> If so, that sounds to me like it's a clock
> for the display data being sent in the 30
> uS stream.

Yep - SCLK for an SPI port.

Each rising (or falling) edge of that clock you
have a new bit of data.  It can run at any speed
it likes then.

see above post for a full explination some
bloke called Scott S. has done.

>The contact pitch is about 60 mils or 1.5 mm. It
>should be pretty easy and safe to solder wires to the contacts.

http://www.littlemachineshop.com/products/product_view.php?
ProductID=1990

--- In Homebrew_PCBs@yahoogroups.com, "Jan Kok" <jan.kok.5y@...> wrote:
>