Jules Richardson wrote:
On Tue, 23 Aug 2011 16:05:05 +0100, Bob Minchin wrote:

Jules Richardson wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter face.
However, it's a bit bright for night time. Any clues about dimming it?
Can't get a data sheet for it - came from the far east. The PCB has a
single processor and two regulators - one 5 volt and one 3.3v. I'd
guess the latter is for the display. But being surface mount, rather
difficult to suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

Most LED displays are multiplex driven 7 or 8 rows x 3 columns

Yep - that's why I was checking, as the OP gave the impression that the
board just had the LEDs, main IC, and a couple of voltage regulators. I'm
surprised* that it doesn't have any resistors between the segments and
the control chip's outputs, and perhaps a trio of transistors used for
multiplexing.

* but maybe it really is a "voltmeter on a chip" and so everything's
built-in :-(

cheers

Jules

It could even be a PIC type processor but that might be too costly even
if a masked programmed version. Only bonus for a high volume chip would
be things like brightness control would be included.

Bob