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Elks 11th Hour Clock |
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I was asked to see if I could repair this 11th hour clock for a local Elks Lodge. The hour of 11 has a tender significance. All Elks Lodges will toll 11 strokes with a toast to remember all departed Elks. This one was made in the late 1970s by the 11th Hour Manufacturing Company in Illinois.
It was a simple design with TTL circuitry and utilized a doorbell for the chime and 7.5W 120V lamps to light up the entire face. It supposedly would only chime once but was completely dead when I received it. The circuitry inside was as line mains potential due to the SCR switch for the lights. The power supply tantalum capacitor was shorted so I replaced it. However, it was still dead. All of the nomenclature on the ICs and 3 terminal regulator was sanded off supposedly to protect the design. Well, it also prevented any service. I surmised the regulator was a 7805 based on the voltage of the tantalum and replacing it brought back just the single chime. It would have been a lot of work to reverse engineer and figure out what all the ICs were. I decided it would be better to just redesign it.
I thought that the entire clock could run on 5V with LED lighting, a microprocessor for control, and a mp3/wave player/speaker for the chimes. I wanted each of the numerals to light up with the chimes so decided on 11 hour LEDs and a center LED. I needed a couple of control lines for the mp3/wave player and an input switch. I chose an ATTINY2313 as it had the right number of IO pins.
My first effort was to determine how to illuminate the hours. The face was fairly opaque so I chose 1W LEDs. I needed to collimate them so they would only light up the individual hour numeral and chose to mount them inside the 120V AC sockets. I used three solid wires to solder to the three eyelets. The collimation works quite well for the hour digits.
I only program in assembly so wrote a quick program to control the 12 LEDs and sounds. The program only runs once and then stops. That prevents a false trigger if it is left powered on. An external 5V 2A regulated supply was used so inside the clock is only low voltage. I didn't even use the timer for the 5 second delay but instead used a firmware timing loop.
I used a DF Mini Player module for the Oscilloscope Music exhibit at the vintageTEK museum and it worked well, so I used one for the audio. It will directly drive a speaker with sufficient volume and has two hardware trigger inputs to play different mp3/ wave files. I used a gong sound for the hours and Big Ben chimes at the very end. These inputs were designed for switches to ground, so I used transistor drivers. The sound files are on a micro-SD card and the gong needs to be file 001 and Big Ben chimes file 005. Of course you could substitute any sound files on the micro-SD card.
Feel free to use this design and files. If you do a PCB I would appreciate the artwork.
11th Hour Clock ATTINY2313 hex file Fuse Bits: Ext=0xFF High=0xDF, Low=0xE4 Int RC Osc. 8 MHz startup long
Construction
I found that about 250 mA worked well for the hour LEDs and 180 mA worked well for the center LED. I used transistor drivers for each of the LEDs. In this build I chose separate resistors for each of the hour LEDs since I thought I might have to modify some. The lighting was uniform, and since only one hour is on at a time, I could have wired all the LED anodes together with a single series resistor. With the 1W LEDs I used, 5R7 0.5W worked well for the hour digits but were expensive, so I used two paralleled 11R5 1/4W resistors. A 13R 1/2W resistor worked well for the center LED.
I didn't take the time to lay out a PCB but hand wired it. The top connectors are the hours and center LEDs. The bottom connectors are power, trigger switch, and speaker. You can see the micro-SD card plugged into the DF Mini Player module. You can also see all of the individual hour LED resistors.
The inside wiring is pretty simple. I mounted an 8" speaker to the rear in the cutout for the doorbell. The power supply is external to the clock.
I added a label to show the lineage of this clock over the past 45+ years.
Here's a video of the clock in operation.