Resistor is required.
Forward current on the datasheet is maximum rating.
I don't see any current limiting resistor in the datasheet, diodes will
dump current until they self destruct unless you limit them with a
resistor.
The segments are 12V because they are 5x series diodes, forward voltage
drop is typically 2.5v * 5 = ~12V
NOTE! Decimal point is a single LED, therefore you will likely blow it out
if you use 12v.
-Dan
On Sat, 2 Jan 2021, Bill Stanley wrote:
Doing a bit or research, I believe the LED display is (or is similar) to an
obsolete part, ELS-4005SURWA/S530-A3 ,
datasheet at
https://media.digikey.com/pdf/Data%20Sheets/Everlight%20PDFs/ELS-4005SURWA_S530-A3.pdf
This part matches the size and pinout of your units. Each segment has 5
series LEDs with an If of 25mA and a Vf of 10-12V, thus no resistors
required.
-Bill-
On Saturday, January 2, 2021 at 8:26:58 AM UTC-8 Bill Stanley wrote:
From a software point of view the Arduino should be able to generate the
signals. It is possible that a SPI interface will do a lot of the serial
conversion.
In terms of a library, once the serial format is known and if (big if) a
SPI port can be used, there is probably some library code that could be
used as a starting point. I'm sure someone can give a lot better
information.
There are a couple of things that I am not sure about based on your
photos...
- You indicate that the LED displays are 12V. My guess is that the
linear regulator with an adjustment resistor for brightness actually drops
the voltage (13.6V) to the display The 4.6V is probably the logic Vcc.
- One thing I didn't see were current limit resistors. I wonder if
they are built into the display?
- I am also guessing that the displays are not multiplexed just based
on the fact that if they were multiplexed, the sequencing would probably
need to be handled by the missing "host" since I don't see anything on the
board to handle that. Also the fact that the 00.00 comes up and is not
extremely bright makes me think that current/brightness control is built
into the display and the segments/digits are not multiplexed.
I would be willing to take a look at a board and attempt a hardware
reverse engineer to generate a schematic for you. I could also take a stab
at generating a document on the driving of the unit.
-Bill-
On Saturday, January 2, 2021 at 7:40:33 AM UTC-8 Jeffry P wrote:
Will an Arduino work? Is there alibrary that will produce these signals?
On Thursday, December 31, 2020 at 4:19:22 PM UTC-6 Bill Stanley wrote:
Correct, these are a differential receiver to receive the serial (BCD)
information, 2x8 shift registers to convert to parallel BCD and 4 BCD to
seven segment LED drivers.
With a bit of sleuthing, the schematic can be reverse engineered,
reverse engineer the serial format and build or use a COTS CPU like Pi to
display anything you wish.
The power supply connector also probably has the serial data (look for
wires going to the AM26LS32). Somewhere there will be a connection to
inject that serial stream.
-Bill-
On Thursday, December 31, 2020 at 1:30:17 PM UTC-8 bani wrote:
These are not standalone clock displays. They are driven by an external
controller over serial. If the controller is not integrated into the
PSU,
then you are missing the external controller module.
Personally I would just design a completely new clock using the LEDs.
-Dan
On Thu, 31 Dec 2020, Jeffry P wrote:
I purchased a clock display system from a USPS auction about 20 years
ago
and recently rediscovered it in my storeroom. There are 20 displays
and a
power supply. The displays were housed in a metal enclosure that has
a
window cutout for the LEDs. The window had a piece of red colored
film and
the LEDs were behind. When I plug the power supply in it will light
all 0's
and a decimal point (as seen in photos), but will not start keeping
time.
I'm willing to send one of these boards( at my expense) to someone
who can
help me get the thing keeping time again. I've attached a few photos
with
descriptions of chips that are on the board and voltages measured at
the
power supply connector.
Thank you, Jeffry
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