Tap into 7 seg LCD driver...

What would be the most simple and safe way to derive a clean 'Logic High' (for CMOS 4000 series etc), from each segment of any functioning device which has an LCD display? In this case, i'm seeing an AC square wave of about nine volts p.p. per segment. An Intersil ICL7136 chip is driving the LCD display (as it is designed to do) and the system is running off a nine volt battery.

I have a half built 'Veroboard Lashup' I started over ten years ago as an attempt to do the task using a nice little four pin bridge rectifier for each seg. followed by a smoothing cap and it was a good enough signal to present to the CMOS Digital part of the project.

But I really doubt if this is the best approach in terms of the ICL7136's safety or simplicity in the work required to finish this one-off gadget.

I've done a reasonably large amount of searching, but ended up here (as usual) for these sorts of answers.

Any Ideas? Thanks, Mark

Reply to
Mark Kelepouris
Loading thread data ...

Gooogle "Driving LCD segments directly"

There are too challanges to overcome.

a) The LCD segments are matrixed - not a static waveform (pulsed)

b) The LCD waveforms are not static (AC waveform)

So your logic will need to detect the the suttle differences in the AC waveforms as well as the pulsed waveform.

Might be easier to to do it another way

Joe

Reply to
Joe G (Home)

On page 9 of this PDF

formatting link
there is a circuit to select the decimal point. My thought is to XOR a segment with the backplane signal and latch the data in a FF when the backplane is not active.

You might eliminate the XOR by latching the segment when NOT backplane.

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

Reply to
Jon

Feed the segment outputs into a latch (eg: several HEF4044) and clock the latch from the backplane pin. (possibly with a slight phase shift and/ or signal inversion interposed)

or you could feed the segment outputs straight into MM74C915 if you're using them, and use their internal latches, (same scheme for clocking the latches)

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

Reply to
Jasen Betts

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.