Fred's like Sloman and Phyllis, always down.
Nonsense, it is a tentative search result, and has nothing to do with up, down or sideways.
Fred's like Sloman and Phyllis, always down.
Wild idea...
Convert segments to bits via photo-diode-driven comparators
("comparators" might be as simple as inverters with a resistive
pull-down on the inputs)
Then run a counter loop that drives a 7-segment encoder chip
Bit compare using something like a 74HC688
whit3rd said:If you use phototransistors in series to make AND functions, and in
parallel to make OR functions, I'm thinking there's a few ways to make
the four bits with five or six photosensors. But, I'm too lazy to
figure all the combos (42 AND and 42 OR as well as seven single-segment
sensors).
I'd try first to get an analog pickoff of the thermosensor, and use an
isolator
to read out its analog signal (the VCO of a CD4046 into an optoisolator)
so
as to get a digital signal into the PLC.
If you DO decide to read the bright/dark of the display, be aware that LED
displays are usually multiplexed (everything that looks bright is actually
blinking
on an unknown schedule). A webcam does NOT simplify things as much as
you might like.
A USB video camera that allows for a long exposure would work fine.
Your character recognition software can either resolve the +/- LSDDon Y said:A USB video camera that allows for a long exposure would work fine.
You have to worry that the "data" doesn't update during the
"exposure" -- regardless of whether your exposure is via a
camera or something watching segments (optically or electrically).
E.g., if two successive values are 39.9 and 40.0, do you see
these? Or, 30.0, 30.9, 39.0, 49.0, 49.9, 40.9, etc.? The
OP hasn't indicated what the display (data) update rate is.
Nor whether the display is multiplexed, etc.
[All things that can be *measured* but nothing that can be
settled upon a priori]
You have to worry that the "data" doesn't update during the
"exposure" -- regardless of whether your exposure is via a
camera or something watching segments (optically or electrically).
E.g., if two successive values are 39.9 and 40.0, do you see
these? Or, 30.0, 30.9, 39.0, 49.0, 49.9, 40.9, etc.?
even 98.8
you need to 'debounce' each segment. (or digit, or reading)
Well yes and no. Look up a 7447. And thanks to it, it is usually digits
that are scanned rather than segments.
Yes, you have to hunt for and lock into the refresh cycle.
Fun exercise perhaps, but impractical to do it in hardware. Just program a micro for it.
---
Yes, of course, and they seem to apply to all of us who limit
ourselves to a single path.
---
Actually the scan rate is probably much higher than the update rate.Falls out of the equation. Sample each segment while "off"
(which, in fact, may not actually be off -- if the driving
interface isn't smart enough to insert a dead-time between
column updates) to establish a baseline for each emitter/detector
pair. Then, see what the maximum signal you *ever* see is
(over the integration period). Set slicing level somewhere
between these extremes.
If a lit segment only sees a ~30% duty cycle, it's still better
than the 0% that an unlit segment sees!
What you have to worry more about is synchronizing with the
*data* update interval (i.e., when the next "value" will appear
in the digits).
And, whether the new value will appear the same way each time
(i.e., is the display update rate frequency locked to the digit
refresh rate?)
Well yes and no. Look up a 7447. And thanks to it, it is usually digits
that are scanned rather than segments.
?-)
You think everything can be done with a micro but, as everyone knows,
it's all analog when you get down to the nitty-gritty >:-}
Can you show us how you would do it with a micro... two digits only to
make it "easy" for you >:-}
Sounds like more time to program the micro than to build a hardware
version ;-)
Actually the scan rate is probably much higher than the update rate.
On Mon, 11 Nov 2013 14:55:45 -0800 (PST), Lasse Langwadt Christensen
Sounds like more time to program the micro than to build a hardware
version ;-)