Pinout diagram
Summary specifications
Full pin reference
| Pin | Name | Group | Direction | Levels | Description |
|---|---|---|---|---|---|
| 1 | 1A | I/O | Bidirectional | Analogue/digital I/O | Switch 1 signal I/O (A side). Bidirectional: passes the signal to 1B when 1CTRL is high; high impedance when 1CTRL is low. |
| 2 | 1B | I/O | Bidirectional | Analogue/digital I/O | Switch 1 signal I/O (B side). Bidirectional: passes the signal to 1A when 1CTRL is high. |
| 3 | 2B | I/O | Bidirectional | Analogue/digital I/O | Switch 2 signal I/O (B side). Bidirectional: passes the signal to 2A when 2CTRL is high. |
| 4 | 2A | I/O | Bidirectional | Analogue/digital I/O | Switch 2 signal I/O (A side). Bidirectional: passes the signal to 2B when 2CTRL is high. |
| 5 | 2CTRL | Control | Input | CMOS, 0 V / VDD, active high | Switch 2 control. High closes switch 2 (low impedance between 2A and 2B); low opens it (high impedance). |
| 6 | 3CTRL | Control | Input | CMOS, 0 V / VDD, active high | Switch 3 control. High closes switch 3 (low impedance between 3A and 3B); low opens it (high impedance). |
| 7 | VSS | Ground | Power | 0 V | Negative supply (ground). |
| 8 | 3A | I/O | Bidirectional | Analogue/digital I/O | Switch 3 signal I/O (A side). Bidirectional: passes the signal to 3B when 3CTRL is high. |
| 9 | 3B | I/O | Bidirectional | Analogue/digital I/O | Switch 3 signal I/O (B side). Bidirectional: passes the signal to 3A when 3CTRL is high. |
| 10 | 4B | I/O | Bidirectional | Analogue/digital I/O | Switch 4 signal I/O (B side). Bidirectional: passes the signal to 4A when 4CTRL is high. |
| 11 | 4A | I/O | Bidirectional | Analogue/digital I/O | Switch 4 signal I/O (A side). Bidirectional: passes the signal to 4B when 4CTRL is high. |
| 12 | 4CTRL | Control | Input | CMOS, 0 V / VDD, active high | Switch 4 control. High closes switch 4 (low impedance between 4A and 4B); low opens it (high impedance). |
| 13 | 1CTRL | Control | Input | CMOS, 0 V / VDD, active high | Switch 1 control. High closes switch 1 (low impedance between 1A and 1B); low opens it (high impedance). Note: this control is on pin 13, not adjacent to switch 1 signal pins 1 and 2. |
| 14 | VDD | Power | Power | +3 V to +18 V | Positive supply. Decouple with 100 nF close to the pin. |
Common uses and repair diagnostics
The CD4066 is the 4000-series quad bilateral switch — four independent analogue switches in a 14-pin DIP, each with its own control input. When the control is high, the switch closes and passes the signal in either direction; when low, the switch opens and the two signal pins are high-impedance. The switches are bilateral, so the signal pins are true I/O — it does not matter which side is the input and which is the output. The control pin numbering is not adjacent to the switch it operates: switch 1 uses signal pins 1 and 2 but its control is on pin 13, which is the trap for anyone who assumes the control sits next to its switch.
The CD4066 is the standard analogue switch on boards that need to route audio, video or analogue signals under digital control. It switches audio sources in mixing desks, routes video signals in display multiplexers, and builds the sample-and-hold and analogue multiplexer stages that retro instruments and test equipment rely on. The bilateral design means the switch passes the signal in either direction, so it works as a multiplexer (one input to many outputs) or a demultiplexer (one output to many inputs) with the same wiring. The on resistance is low enough for most audio and slow video work, though not for fast digital buses.
The trap with the CD4066 is the control pin numbering. Switch 1 uses signal pins 1 and 2, but its control is on pin 13 — the opposite corner of the package. Switch 2 control is on pin 5, switch 3 control on pin 6, switch 4 control on pin 12. A board laid out assuming the control sits next to its switch will wire the wrong control to the wrong switch, so always verify against the datasheet.
- Confirm pin 14 (VDD) is within 3 to 18 V and pin 7 (VSS) is at 0 V. The signal range is VSS to VDD, so signals outside this range can damage the switch.
- Drive a control high and check the matching switch closes (low resistance between its two signal pins). Drive it low and check the switch opens (high impedance). A switch that does not respond has a dead control input.
- If a switch is stuck closed or open, check the control pin — the numbering is not adjacent to the switch, so verify against the datasheet before assuming the switch is dead.
- Measure the on resistance at the expected signal level: it rises near the supply rails, so a signal near VDD or VSS may not pass cleanly.
- If the chip runs warm, suspect a signal outside the VSS-VDD range or a shorted switch — CMOS should draw microamps at rest.