Re: DC503 Not Working

Harvey White

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).


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.


On 8/4/2020 6:46 PM, Stephen wrote:
On Tue, Aug 4, 2020 at 11:17 AM, Harvey White wrote:

Once you get the extender, check the strobes on each of the digits.

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