Pencilbox, by E&L Instruments, is a Logic Designer aimed at allowing a user to quickly build a simple logic circuit to interface to a microprocessor.

It can fulfill modest requirements for the design and study of gates, counters, multiplexers and can even interface directly to a microprocessor. (LD-1 Pencilbox User Manual, introduction)

The Pencilbox runs off either 4x “C” Size batteries, or a 5V main PSU. The kit contains the following features:

  • 8 LED Logic Indicators
  • 8 Logic Switches
  • 1kHz Clock (adjustable via external capacitor)
  • 2x debounced buttons
  • Tie point connections to all devices
  • Logic Indicator transparent latches can be reassigned to output drivers
  • Solderless Breadboard

Although the LD-1 is now obsolete, an alternative version is still for sale from the TechEdu website.

The price of the LD-1 Pencilbox was $210 when it was discontinued (suspect around 2018). Although it is unknown when the Pencilbox was first designed, revision “C” of the schematic was done in September 1981, with a futher revision “D” in June 1983.

The User Manual for the LD-1 is available online from the Global Specialists website.

Year1981
Make & ModelE&L Instruments
LD-1 Pencilbox
GenerationLogic Trainer
CPUNone
Speed1kHz (adjustable)
RAM & ROMNone
Power4x “C” size batteries
Exhibit No.1335