Scope Clock TTL (SCTTL)

What if you could reliably tell the time using an old cathode ray tube, nothing but transistor logic and see it counting in real time all in an elegant case? Well now you can… read on.

The SCTTL in Both Horizontal and Vertical Variations

The Scope Clock TTL (SCTTL) uses only TTL logic, a 32KHz TCXO (Temperature Compensated Xrystal Oscillator) and some very ingenious electronics to tell the time without a microprocessor in sight! Available in both horizontal and vertical arrangements, these clocks are unique indeed. SCTTL includes PIR circuitry to avoid driving the cathode ray tube without anyone in the room to view the clock and also some simple logic to move the display around the face of the tube every minute to avoid phosphor burn. A set of LEDs indicates the binary counting from the TTL chips and buttons are present to set the hour, minute and a seconds hold. There are also provisions to customize the font and colons displayed (requires some disassembly) as all this information is held in an EEPROM that can be reprogrammed or the factory pre-installed options selected by the means of pin headers.

SCTTL Vertical Design
A Front Surface Mirror Reflects the Time

The vertical SCTTL pays homage to the old Simpson Mirroscope from the 1950’s. This design allows a very compact footprint for the clock and ample space to show off the inner workings in its glass-effect acrylic case. Adjustment pots are accessible through the side of the case to adjust focus and the position and size of the display. The TTL LED brightness can also be adjusted to suit taste. The mirror is a high-quality front surface mirror to avoid unwanted multiple images from refraction.

The horizontal clock is a more traditional layout with a neck support and a front facing cradle for the cathode ray tube. This layout also allows the easy viewing of the LEDs and their logical counting.

The Horizontal SCTTL Clock
The Horizontal Layout - Note the Orange Glow From The Cathode Ray Tube Heater
LEDs Light Up The Clock Nicely
3D Printed Socket Holder and Neck Support

There is also an option for a rechargeable NiMH battery backup board. Should the power be interrupted, then this add-on ensures that the TTL logic keeps the correct time until the power is restored.

Rechargeable Battery Backup Should The Power Be Interrupted

For those interested in building their own SCTTL clock from a kit, then they can be found for sale at this link. You can also find the kit instructions for download here. 

Horizontal Clock Dimensions: 295mm x 130mm x 180mm (height of face) - Vertical Clock Dimensions: 130mm x 135mm x 315mm (lid closed), 420mm (lid open)

Prices for complete clocks are based upon the options you choose including acrylic color, battery backup, case style, type of CRT etc. If you wish to buy one then please contact me here. The availability of these is limited to the cathode ray tubes on hand.

Currently, the following CRTs have been proven compatible: (note they all have a rectangular screen aspect)

  • 3SP1
  • 3ASP1
  • 3XP1
  • D8-11
  • D9-10
  • 16ЛО3И (quite large!)
  • 3AYP1
Long persistence phosphors may not work that well with the clock and dimmer phosphor colors like P7 may be too dim for daylight use. Examples of all these in use can be found in the customization manual here..