Homebrew PCBs

--- 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