MM5314N clock chip replacement (2023) with source files

Описание: Update: 2026 Was the project halted (for ever?)
Well, no.
I am about to do a second try based on a project done by another German.
It was about making an energy efficient alarm clock, based on BASCOM code, more human readable than assembler code.
http://jtxp.org/tech/netzuhr.htm (2008)
BUT. that clock does not provide showing the seconds on display.
It provides alarm function the MM5314N does not provide, I DO NOT NEED.
Waste of memory space on the tiny AVR chip. We will drop it.
So, some struggling is to be expected.
Well, lets see what we can can make out of it now.

pre-BETA files released. DL from project folder https://drive.google.com/drive/folder...

PCB gerber files, pin swap chart, free source code, needs few modification.

Update: September 2023
I have made it, up & running the core functions, a replacement for the rare and expensive MM5314N.
It is based on an ATMEL microcontroler.

The goal:
Replace a rare & expensive old 1970's National Semi clock chip used on projects of mine.
It is still work in progress. It will not work for everybody.
As usual I will publish it under "CC 3.0 no commercial license" when done.
https://drive.google.com/drive/folder...
See the respective project sub folder, it holds the related docs like the simplified schematics.

When You watch the video with no f*** Google scripting actions like "autostart" the pcb layout with pin remap table can be seen at the very begin.
Original code was taken (& modified by me) from this website
https://web.archive.org/web/202309272...

Either wire up the pins directly or change the code according to the needed pin assignment changes for using the desired pcb layout as shown. See the table & layout.

Upd: I had assumption the higher Vcc driving only the indicators now could put danger on the ATTiny.
Read ATMEL doc2508 "Zero crossing detector using AVR".
The app note covers reading the voltage from AC mains with no transformer in between!
They do recommend using the internal clamping diodes and adding a resistor for the purpose of detecting the voltage crossing the zero line.
It is a simple method of driving an existing ("high voltage") part of the clock by using a "low" voltage microcontroller.

Having installed current limiting resistors the suspected issue can be ignored entirely.
Additionally reducing the now unwanted high DC generated from AC mains voltage provided by the stock power transformer helps.
Original transformers can be replaced by using an 7-9 V DC power adapter (wall wart).
We do not need the AC line for clock pulse generation any longer.

A.t.m. it runs on my Optoelectronics 850-4 clock remake with small modifications.

The replacemnet is using a common 8bit microcontroller.
The current driving the segment driver transistors is been limited by using EXISTING base resistors.
I have put those limiting resistors on the LED segment driver transistors when I redesigned the pcb layout 7 month ago. I had it coming.

Those resistors can be found in some (not extremely cheap made circuits) of the old MM5314N clock designs but not on all of them.

Application of the replacement circuitry depends on switching transistors in the existing clock design as used on the Optoelectronics 840-4 kit clock.
To me thats ok.

A.t.m. the very first build I have made (first try = success) drives the common cathode type displays using transistors on the low & high side as well.
Indeed now the Optoelectronics 850-4 clock is driven by an ATMEL ATTiny microcontroler.
I runs in 24h mode (military for US folks).
The "6" & "9" of course DO have the tail.
The shown test build runs on 8MHz internal RC oscillator faster than it would finally do.
The IC pin count is much limited.
Setting up the time works (fast & slow) thanks to the free port pins otherwise used for XTAL.

The digits driver pins have been reorganized.

TODO:
It needs some tweaking to make the fast set, slow set, halt buttons when using the quarz oscillator:

Limitations:
The original 4/6 digit & 12/24h switch mode function can not be used tough.
The O.E. input & hold button do not work.

The actual build uses a tiny small pcb (of the size of a stamp, old guys know for sure what that means).

The pcb layout design work has been finished.
The oscillator will run at 4.194304MHz.
The pcb holds the ATTiny, a quarz resonator, 2 capacitors and a small low power 5volts voltage regulator.