Lcd digital clock turns to 7-seg led display

Hi, I got an LCD digital clock with a AA cell supplies, but the LCD is now dark, and the soft circuit linked from PCB is broken as well.
Any one help to turn to 7-segment LED 4-digit display (maybe drive by extra transistors) connect from 36 terminals on PCB.

Thank so much

CSV

I wouldn't attempt it for several reasons:

1. the signals feeding an LCD are very different to those used with an LCD. For example you will not have individual segment conections and digit drive signals.
2. it looks like you have one (1.5V) or two AA cells (3V) which isn't enough to drive most LED displays. Each segment in a standard display has several LEDs in series which means they need higher voltages to turn them on.
3. 7-segment LEDs are physically much thicker then an LCD so you would have difficulty fitting it in the same box.

If you really want an difficult but interesting project, you could build an entirely new LCD clock into the box but to be honest, it would cost several times more than buying a new one in a store.

Brian.

betwixt said:

I wouldn't attempt it for several reasons:

1. the signals feeding an LCD are very different to those used with an LCD. For example you will not have individual segment conections and digit drive signals.
2. it looks like you have one (1.5V) or two AA cells (3V) which isn't enough to drive most LED displays. Each segment in a standard display has several LEDs in series which means they need higher voltages to turn them on.
3. 7-segment LEDs are physically much thicker then an LCD so you would have difficulty fitting it in the same box.

If you really want an difficult but interesting project, you could build an entirely new LCD clock into the box but to be honest, it would cost several times more than buying a new one in a store.

Brian.

Click to expand...

Thank you Brian,

what I need is an extra 7-segment LED display (maybe 5.6x13" my own design) and drive by transistors and take only the signals from PCB pins. My clock supply with single AA cell (1.5V) but I measured the voltage between negative and LCD pins are mostly 1.9VDC, I am not sure whether there is some pulse signals or not since I am not fully knowledge in the digital and program field but my logical think that we absolutely could take the signals to drive the bigger LED display. The stuck now is the appropriately connection from PCB pins to segments/digits of display.
I am intending to do a experiment to define which pin to drive which segment/dot points/digit by matrix LED.

I do appreciated if any good idea advised.

Thanks a lot

CSV

How will you check the board is in good condition or not and how will you find the pin details of the output pins???

LCDs are not driven the same way as LEDs, they are 'AC' driven instead of DC, It isn't real AC but the polarity across the segment connection and the backplane is reversed at around 200Hz or so. When you measure the higher voltage its probably because of the signal shape and polarity, you really need an oscilloscope to measure it and see the waveform. Although there is a unique way to drive each segment, you will almost certainly find that some segements are joined to others but use different backplane drivers. To decode it back to true 7-segment signals you need one XOR logic gate per segment so you may have to use lots of ICs to do it. It's a lot more complicated than it first appears. Most LED 7-segment displays need more voltage than you have available anyway, ones with more than a single LED behind the segment window need 3V or more to light them.

Brian.