Introduction

This is a kit of the "How Things Work" series. Over the door of a shop, a museum or a metro car hangs an unnoticed little box, and in the evening the owner knows how many people came in today and how many are still inside. Inside it are two beams and a few chips. In this kit you build such a counter completely: from the chips after the datasheet to two displays.

• lesson 1 — an IR beam and the first chip, CD4011: the "someone passed" lamp stays on until Reset;
• lesson 2 — the flip-flop the counter is made of: load, flip, hold;
• lesson 3 — the CD4029 counter: up and down, binary and decade — after the logic diagram from the datasheet;
• lesson 4 — the CD4511 decoder: a binary code becomes a digit on the display;
• lesson 5 — direction: the beam blocked first is the way in;
• lesson 6 — the device: "inside" and "total in" displays.

What you need

The kit is standalone. The gates NOT, NAND, NOR, AND, OR, XOR — from any kit of the series or from lesson 0. Each chip is built from gates and the chips of earlier lessons: the CD4029 — from four F/F flip-flops, the device — from CD4011, CD4029 and CD4511.

How big it is

CD4011 — 16 transistors, the F/F flip-flop — 68, CD4029 — 454, CD4511 — 204. The device with two displays: two CD4011, four CD4029 and four CD4511 — 2,664 transistors.

A model of real chips

The CD4011, CD4029 and CD4511 are made by Texas Instruments, and each has a datasheet with a logic diagram. We build the chips after these diagrams gate for gate, with the same pin names; the power pins VDD and VSS are not needed — power in the simulator is shared. If you build with wires rather than with labels, lessons 3 and 6 have the circuits as one drawing.