1. The oscillator and countdown circuit with a 14-stage divider using five different frequencies.

  2. A 3-function circuit to:  a) time how long the display is lit  b) turn on the seconds when the button was held down and  c) set the minutes and reset the seconds to zero.

  3. A seconds counter circuit that additionally allowed for zeroing the seconds. This circuit also rolled over the seconds from "59" to "00".

  4. A minutes counter circuit. This circuit also rolls over the minutes from "01" to "59" and triggers the display to the next hour indicator.

  5. An hour counter that simply counts the hours from "1" to "12".

  6. An automatic light sensory circuit utilizing 3 separate sensors for ambient light.  This controls the current fed to the LEDs to conserve battery life.

  7. This is a logic circuit that switches the power to the six separate binary code decoders mounted on the display side of the module. 

(Above) The display side with the balance of 13 ceramic boards.  There are 3 separate custom HP-5082-7000 numerical LED displays.  Hewlett Packard would not license Electro/Data to build numeric displays using their patent.  Electro/Data redesigned the layouts to squeeze them down.  Drawings were sent to a local company which laid down the gold tracings on the ceramic boards.  Because the Driver Chip was a proprietary HP product, the boards were then sent to HP to have the Chip and LEDs mounted.  The metal framework for both halves of the module were made of Beryllium Copper and fastened together as a unit.

(Below) Both sides of the module potted in epoxy to preserve all those 2,200 connections and to reduce shock to the module.