Build kit

The Visitor Counter

The fourth kit in the How Things Work series. Over a shop door there are two invisible beams, and in the evening the owner knows how many people came in and how many are still inside. You build such a counter from transistors: three real CMOS 4000 chips after the Texas Instruments datasheets — the CD4011, the CD4029 counter and the CD4511 decoder, gate for gate, with the same pins — an IR pair, a direction latch and two displays: "inside" (in +1, out −1) and "total in". For building with wires — the circuits as one drawing. A standalone kit. 2,664 transistors.

Start

This kit is free: all lessons are open, no sign-up needed.

INSIDETOTAL IN

CD4011 · CD4029 · CD4511 · 2,664 TRANSISTORS

What is inside

  1. Introduction
  2. History: how light learned to count people
  3. Lesson 0. Gates from transistors: for those who start from scratch
  4. Lesson 1. The beam and CD4011
  5. Lesson 2. The F/F flip-flop
  6. Lesson 3. The CD4029B counter
  7. Lesson 4. The CD4511B decoder
  8. Lesson 5. Direction
  9. Lesson 6. The visitor counter
  10. Summary
  11. All the parts
  12. Instructions in pictures