7-segment LCD to BCD decoder ?

Just in case any hacker-types here (purists turn away now)
Got a bit bogged down with the first stage of extracting 7seg data.
Chinese made kit with uC buried under black epoxy.
20 LCD lines wiht nice ATE pads for soldering external wiring to.
Decided on cutting and re-making 3 LCD traces , as all segments are lit 
at POST, to determine the multiplexing structure. 4 backplanes and 16 
channel , 4-level drive voltages, for digits and anunciators. 2 channel 
per digit split vertically into abc,dot / defg
In this case to extract the segment on/off data, doubt it is generally 
applicable though . I'm only interested in 2 digits, so 3x4 matrix of 3 
BP (dot , c and d not used) and 4 channels. Used a bridge of 4x4148 and 
100nF, then a "pull-up" resistor for the off state, connected lowside 
rectified DC to supply for each of the 10 monitored pairs.
Using the original 3.3V supply and feeding the floating quasi-DC low and 
high to 4070 exor gate inputs of one gate per digit, the low-DC side off 
state needs pulling high to give reliable Exor "0" output. So LH for H 
out,ie "on" and HH for L out,ie "off"
Pull up needs to be 100K or higher to avoid disrupting the original LCD 
display, underlying uC operation unaffected.
Now to progress to original query placed here, as at the moment just 2 
simple unmultiplexed 7 segment LED displays reading the same as 2 LCD 
digits (ignoring c and d and dot segments)

On a sunny day (Thu, 23 Oct 2014 14:20:47 +0100) it happened N_Cook
<diverse@tcp.co.uk> wrote in <m2avba$s9r$1@dont-email.me>:

>Just in case any hacker-types here (purists turn away now)
>Got a bit bogged down with the first stage of extracting 7seg data.
>Chinese made kit with uC buried under black epoxy.
>20 LCD lines wiht nice ATE pads for soldering external wiring to.
>Decided on cutting and re-making 3 LCD traces , as all segments are lit 
>at POST, to determine the multiplexing structure. 4 backplanes and 16 
>channel , 4-level drive voltages, for digits and anunciators. 2 channel 
>per digit split vertically into abc,dot / defg
>In this case to extract the segment on/off data, doubt it is generally 
>applicable though . I'm only interested in 2 digits, so 3x4 matrix of 3 
>BP (dot , c and d not used) and 4 channels. Used a bridge of 4x4148 and 
>100nF, then a "pull-up" resistor for the off state, connected lowside 
>rectified DC to supply for each of the 10 monitored pairs.
>Using the original 3.3V supply and feeding the floating quasi-DC low and 
>high to 4070 exor gate inputs of one gate per digit, the low-DC side off 
>state needs pulling high to give reliable Exor "0" output. So LH for H 
>out,ie "on" and HH for L out,ie "off"
>Pull up needs to be 100K or higher to avoid disrupting the original LCD 

I wrote a seven segment to RS232 parser a while back:
 http://panteltje.com/panteltje/7s_parser/index.html
   see the youtube demo.
Needs a cheap webcam, advantage: no physical contacts.

>display, underlying uC operation unaffected.
>Now to progress to original query placed here, as at the moment just 2 
>simple unmultiplexed 7 segment LED displays reading the same as 2 LCD 
>digits (ignoring c and d and dot segments)
>

for
4070 exor gate inputs of one gate per digit
read
4070 exor gate inputs of one gate per segment

On 2014-10-23, N_Cook <diverse@tcp.co.uk> wrote:
> Just in case any hacker-types here (purists turn away now)

> Got a bit bogged down with the first stage of extracting 7seg data.
> Chinese made kit with uC buried under black epoxy.
> 20 LCD lines wiht nice ATE pads for soldering external wiring to.
> Decided on cutting and re-making 3 LCD traces , as all segments are lit 
> at POST, to determine the multiplexing structure. 4 backplanes and 16 
> channel , 4-level drive voltages, for digits and anunciators. 2 channel 
> per digit split vertically into abc,dot / defg
> In this case to extract the segment on/off data, doubt it is generally 
> applicable though . I'm only interested in 2 digits, so 3x4 matrix of 3 
> BP (dot , c and d not used) and 4 channels. Used a bridge of 4x4148 and 
> 100nF, then a "pull-up" resistor for the off state, connected lowside 
> rectified DC to supply for each of the 10 monitored pairs.
> Using the original 3.3V supply and feeding the floating quasi-DC low and 
> high to 4070 exor gate inputs of one gate per digit, the low-DC side off 
> state needs pulling high to give reliable Exor "0" output. So LH for H 
> out,ie "on" and HH for L out,ie "off"
> Pull up needs to be 100K or higher to avoid disrupting the original LCD 
> display, underlying uC operation unaffected.
> Now to progress to original query placed here, as at the moment just 2 
> simple unmultiplexed 7 segment LED displays reading the same as 2 LCD 
> digits (ignoring c and d and dot segments)

That seems to have 80 to 90% of the words needed to make it fully 
comprehensible.

with a multiplexed drive I think you need to ignore the middle 
backplane voltages and latch the segment drive when the backplane
is fully driven at one extreme. 

exclusive or is probably not worth the effort. at best you'll get a glitchy 
signal.

-- 
umop apisdn