'READING' a VFD…?
Topic: 'READING' a VFD…?
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'READING' a VFD…?
Apr 20, 2012, 06:04 am
Here's a problem that's been presented to me this week, and I'm looking for ideas:
We have a device controller with a VFD display in which seven particular digits and two annunciators are very important. It would be extremely convenient to be able to monitor them from across the lab either visually or aurally (giving me an opportunity to use a http://www.magnevation.com/SpeakJet.swf !). Each digit has its own cathode, and the segment anodes are all properly chained-together making a nice little multiplexed display.
The controller does a multitude of things with various sensors and signals, and I don't feel like doing more than I have to - so monitoring/processing all those signals is out of the question. The controller has no output lines I could tie-into which would help me.
MY thought was to connect a 74165 (8->1 shift register) to the anode lines (don't know the operating voltages of the VFD yet, but whatever they are I'm not worried about getting them down to TTL levels), and use a 74595 (1->8 shift register) with logic gates (ANDs and ORs - again I'm not worried about level shifting) to the cathodes…
When I set a particular cathode's corresponding shift register bit on the '595 it would be ANDed with that (level-shifted) cathode's signal. All the resultant signals from the cathode position AND gates would be OR'ed onto the LOAD line of the '165. Long-story-short: one-by-one I could latch/capture the anode states for each digit and read them into the Uno and properly decode them. Then I could either drive another display -or- maybe use the SpeakJet to 'read' them out loud (which would be a LOT of fun).
Everything I've seen in the forum relates to using VFDs as (obviously) output devices; has anyone here any experience in, essentially, treating the VFD's signals as an INPUT device? Or is there already an existing chip that DOES this and I'd be 'reinventing the wheel'?
I crave your comments and suggestions.