Re: DC503 Not Working


Stephen
 

On Tue, Aug 4, 2020 at 02:03 PM, Harvey White wrote:


Vocabulary thingie......

A pulse, likely sequential, is (at least at on time) called a strobe.

Take a display with a common anode for all the segments.  It needs to be
connected to VCC (power) to light.  However, there's a limit where the
display continuous power per segment is exceeded. This is not a good
design.  However, if you pulse the LED (segment) with more current than
the continuous rating, but for less time, then the display survives. 
Due to a quirk with human vision, it appears brighter.  So what you do
is connect the source of each digit to a signal (strobe) which in
sequence selects each digit.

The segments drivers themselves are selected so that the current through
each segment (assuming common anode with digit strobe to +vcc, and
segment driver (through resistor) to ground) is the nominal peak current
that they want.

So if all displays were driven in parallel, there'd be one driver chip
per display, no pullup transistor to VCC, and  a lot of chips.  If you
multiplex the displays (please look this up), then you have a sequential
pullup to VCC (called a strobe), a pulldown to ground (called the
segment driver, which determines which segments on which digit are on
when....) and a current which is more than needed for a single digit
(perhaps # digits times current per segment, because you don't know if a
segment is on or off, so you do it per segment).

So:

a scanned display turns on each digit sequentially, with more current
per segment than permitted (steady state but less than pulsed) and with
less chips, but more complex than a few digits. However, as the digit
count goes up, the circuit is simpler. Microprocessors love this kind of
thing.

Harvey
Ok, so you suggest I sweep each digit for a signal at its input? At the ribbon cable connections then...

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