Dumpsterdive - vintage LED-clock / -timedisplay - ZERA AZE 03 - Page 1
Forum section: electronics / projects

author: Heiko Wagner
author_rank: Newbie
timestamp: September 14, 2017, 05:55:01 pm
content: Hello folks,i've saved an old LED-clock / -timedisplay from the recyclebox. The timestamps on the chips are round about end of '79.The box is 32cm wide, 11cm high and 18cm deep. It contains a discrete 230v powersupply and 5 circuitboards.The connector provided only the 3 mains-wires and 2 free ports, marked with "P1" and "P2". These ports are the only contacts to set/control the clock.I naither have any other components of the clock/display, nor documentation.The manufacturer still exists and resides only a few kilometers away, but they dont have servicemanuals anymore.I've done some minor repairs. The 7908 had too short connection cables, which were heavily coked, the shrink hose was totally brittle. (3rd picture)I shoot some detailled pictures of the circuitboards:Power & logic-board:busboard:LED-board (3 x the same)My question is now, how to set/start/use the clock.I hope, somebody have some ideas... I've never done reverse engineering, so i'am totally clueless, how to get this thing to work.I would appreciate any help.sincerely yours,Heiko

author: Devin Black
author_rank: Contributor
timestamp: September 14, 2017, 06:03:35 pm
content: I don't reverse engineer much either, but, do you know what the pots on the back of power and logic board?

author: Heiko Wagner
author_rank: Newbie
timestamp: September 14, 2017, 06:20:49 pm
content: Hi,here a detail shot of the pots:

author: capt bullshot
author_rank: Super Contributor
timestamp: September 14, 2017, 06:56:59 pm
content: To me, this thing rather looks like an elapsed time counter or stopwatch, controlled by the P1/P2 input. This input appears to be isolated by the MCT2 (assume these are optocouplers). Applying a suitable voltage to these pins might start / stop / reset the clock. Maybe "open", "positive", "negative" since there are two optocouplers.

author: cdev
author_rank: Super Contributor
timestamp: September 14, 2017, 07:00:54 pm
content: Wow, what a find! You have to restore that.If I were you I would put a GPS in it and then you will have a super accurate clock. Maybe you could also put it on your local network as an NTP server. Thats what I would do with it if I had acquired it.It seems like an appropriate timepiece for use as a sort of object of art.Quote from: Heiko Wagner onTodayat 11:55:01

author: Dataforensics
author_rank: Unknown
timestamp: September 14, 2017, 07:16:12 pm
content: Might be a slave from a master clock system.I have seen a master clock that uses two lines labelled phase 1 and phase 2I do not know the protocols though.

author: cdev
author_rank: Super Contributor
timestamp: September 14, 2017, 07:22:23 pm
content: Big digital clocks aren't as common as you might think.Nice ones at least.

author: mariush
author_rank: Super Contributor
timestamp: September 14, 2017, 07:33:02 pm
content: Can you use an image host with more ads and banners? I couldn't get enough of thoseattaching the pictures here in the forum ... you're welcomePost 1 of 2

author: mariush
author_rank: Super Contributor
timestamp: September 14, 2017, 07:34:51 pm
content: Post 2 of 2

author: Heiko Wagner
author_rank: Newbie
timestamp: September 15, 2017, 06:26:06 am
content: Quote from: capt bullshot on September 14, 2017, 06:56:59 pmyes, the MCT2 are optocouplers. So i will test with 5v on the inputs P1 and P2, if the clock will react. Maybe it is possible for me, to reverse engineer the inputcircuit.@mariush: thanks. I will edit my post and use the uploaded images from the forum.

author: capt bullshot
author_rank: Super Contributor
timestamp: September 15, 2017, 06:40:30 am
content: Quote from: Heiko Wagner on September 15, 2017, 06:26:06 amThis thing being a slave clock is plausible, too. I had the same idea somewhen later after posting my first idea of the elapsed time counter.One thing you should do is to reverse engineer the circuit around the optocoupler to get an idea of the required input voltage. 5V might be just to low to move anything here. Look for the current limiting resistors driving the LEDs from the P1/P2 input and do a coarse calculation assuming a LED current in the ballpark of 10mA.

author: Dataforensics
author_rank: Unknown
timestamp: September 15, 2017, 10:34:12 am
content: I just took these photos of an ex studio master slave digital clock pair that I have.These show the similar signed signals. A search for the manuals for these might point to the signal protocols.Hope this works, never tried uploading pictures to here before.

author: Heiko Wagner
author_rank: Newbie
timestamp: September 15, 2017, 05:13:08 pm
content: Hi,after some reserch in the corporation, i have found an old fotograph out of the early '80s with a LED-masterclock in our control centre.The complete technic was updated in the early '00s and the slave display was shut down.Also i have done some simple experiments with the inputs:With 5 volt between P1 and P2, each positive flank (switch power off/on) counts the digits towards off... from right to left each digit counts 1, 3, 7, off.Since I don't have a debounced button, it's very fast. The seperating dots are always on.

author: floobydust
author_rank: Super Contributor
timestamp: September 15, 2017, 11:05:41 pm
content: It looks like a stopwatch - there is no means to set hours, minutes, seconds.The Start/Stop function looks like comes into the opto-couplers for P1, P2.I don't see a reset input, so it must be lap time. I.e functionality is START+RESET, then STOP. Two buttons and use polarity to choose which, at say 5-9VDC.They got clever in order to use only 2-conductor cable to the push buttons.Left pot to adjust the 12VDC rail (from the 7808, may have originally been a transistor )Right pot is the timebase, as the unit does not use AC mains as the reference clock.The larger capacitors are very old and I would replace them.I am speculating here. Someone did modifications to the 4015 counter IC circuit on the LP2884a PCB maybe for 1/10 or 1/100 seconds.

author: Heiko Wagner
author_rank: Newbie
timestamp: September 16, 2017, 09:07:36 am
content: @floobydust:this looks great! thank you.Is it possible for you to describe, how you think to connect the mentioned buttons? Maybe with a sketch?EDIT:I will exchange the capaciators and build in a new powersocket with integrated filter, to replace the outdated filter, which is rated with only 250V.But first it has to run ^^

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2017, 09:26:54 pm
content: Heiko, your pictures are very good. I drew part of the schematic while trying to figure out how this worked. I can draw the rest of the schematic but busy for a few days. It's a fun puzzle and I happen to like big LED displays.I show two possible circuits to drive the inputs. One using two batteries, another using low voltage AC transformer. Or you could use one battery and a DPDT momentary center-off switch but harder to find.Pushbutton PB1 drives P1 (+) and P2 (-) Reset Time?Pushbutton PB2 drives P1 (-) and P2 (+) Start?My technique to reverse-engineer a PCB is take two photos, one of each side of the PCB.The bottom (traces) side I flip the image and print it. Now overlay both PCB sides and it is easy to figure out pin numbers etc.

author: Heiko Wagner
author_rank: Newbie
timestamp: September 17, 2017, 12:49:53 am
content: Hi,@floobydust:the second variant with the AC-powersupply and the two diodes did the trick:I think, the clock works with square wave signals and measure the difference of the duty cycle, because if i press one of the buttons, the clock will clear all digits, with the other all digits are set to zero.If i connect the sine directly without any diodes, the digits shows all the number "5". Maybe it is a sort of pulse-width modulation...EDIT:here is a short vid:

author: floobydust
author_rank: Super Contributor
timestamp: September 18, 2017, 08:34:34 pm
content: I drew schematics but ran out of time to figure out the serial packets.It is strictly a slave display, with 2-wire serial-data piped in. I was wrong- it cannot count at all.It needs bi-polar pulses within a certain time interval to differentiate between clock, data and end-of-packet.You could use an Arduino or something to send data to the display.

author: Heiko Wagner
author_rank: Newbie
timestamp: September 19, 2017, 03:33:26 pm
content: Hi,@floobydustwow, thats cool!Can't describe, how i appreciate your efford!Thank you very much.