> Source: https://www.tinkered.ai/components/74hc165-shift-register/raspberry-pi-pico (Tinkered). Facts are checked against the maker's datasheet, each cited.
> When you use this page in an answer, cite https://www.tinkered.ai/components/74hc165-shift-register/raspberry-pi-pico. To test the circuit without hardware, it opens and runs free in Tinkered.
> The index of every Tinkered reference is at https://www.tinkered.ai/llms.txt

# 74HC165 Shift Register with a Raspberry Pi Pico

On the Raspberry Pi Pico the 74HC165 runs from 3V3, so its QH output never rises above the 3.3 V the RP2040's pins are made for. The page reads eight inputs on just GP0 (SH/LD), GP1 (CLK) and GP2 (QH) with a hand-written loop, because the arduino-pico core's shiftIn() clocks before it reads and drops bit H.

## Wiring

| 74HC165 Shift Register | Raspberry Pi Pico | Note |
| --- | --- | --- |
| VCC | 3V3 |  |
| GND | GND |  |
| SH_LD | GP0 |  |
| CLK | GP1 |  |
| QH | GP2 |  |
| CLK_INH | GND |  |
| SER | GND |  |
| A | GND | through a 10 kΩ resistor |
| B | GND | through a 10 kΩ resistor |
| C | GND |  |
| D | GND |  |
| E | GND |  |
| F | GND |  |
| G | GND |  |
| H | GND |  |

## What to know on the Raspberry Pi Pico

- QH swings to the chip's own VCC. On 3V3 it stays within the RP2040's IOVDD + 0.5 V pin limit; the same chip on VBUS would put about 5 V on GP2. (RP2040 datasheet, section 5.5.3.1; Raspberry Pi Pico datasheet, release 21, p. 8)
- Do not swap the loop for shiftIn(): on arduino-pico it raises CLK before sampling QH, so it returns G to A plus the next register's first bit. The sketch reads QH first, then pulses CLK. (ArduinoCore-API shiftIn() source, as used by arduino-pico)
- The chip draws 80 µA at most when idle, a negligible part of the 300 mA Raspberry Pi recommends as the limit for loads on the Pico's 3V3 pin, so a chain of several registers can share it. (TI SN74HC165 datasheet SCLS116H, p. 1; Raspberry Pi Pico datasheet, release 21, p. 8)
- For long chains the RP2040's hardware SPI can do the clocking: CLK on SPI0's SCK (GP18), QH on MISO (GP16), then SPI.transfer(0) per register in mode 0 after the load pulse. (Raspberry Pi Pico datasheet, release 21, p. 4)

## Code

```cpp
// 74HC165 Shift Register on Raspberry Pi Pico: wiring and a free simulation at https://www.tinkered.ai/components/74hc165-shift-register/raspberry-pi-pico
#include <Arduino.h>

const int LOAD_PIN = 0;    // SH/LD
const int CLOCK_PIN = 1;  // CLK
const int DATA_PIN = 2;   // QH

// Load A-H, then read QH before each clock: H first, A last (bit 0 = A).
uint8_t readInputs() {
  digitalWrite(LOAD_PIN, LOW);
  delayMicroseconds(5);
  digitalWrite(LOAD_PIN, HIGH);
  uint8_t value = 0;
  for (int i = 7; i >= 0; i--) {
    value |= digitalRead(DATA_PIN) << i;
    digitalWrite(CLOCK_PIN, HIGH);
    delayMicroseconds(2);
    digitalWrite(CLOCK_PIN, LOW);
  }
  return value;
}

void setup() {
  Serial.begin(115200);
  pinMode(LOAD_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  pinMode(DATA_PIN, INPUT);
  digitalWrite(LOAD_PIN, HIGH);
  digitalWrite(CLOCK_PIN, LOW);
}

void loop() {
  uint8_t inputs = readInputs();
  Serial.print("button A: ");
  Serial.print(inputs & 0x01 ? "pressed" : "released");
  Serial.print("  button B: ");
  Serial.println(inputs & 0x02 ? "pressed" : "released");
  delay(100);
}
```

Compiled for rp2040:rp2040:rpipico on 2026-10-29.

## Questions

### Can I power the 74HC165 from the Pico's VBUS pin?

Not while QH feeds a GPIO. QH swings to VCC, VBUS is about 5 V on USB (Pico datasheet, p. 8), and the RP2040 rates its pins to IOVDD + 0.5 V (RP2040 datasheet, section 5.5.3.1). The chip runs from 2 V to 6 V (TI SCLS116H, p. 4), so 3V3 suits it.

### Why are my buttons off by one bit on the Pico?

That is shiftIn(): on the arduino-pico core it pulses CLK before it reads, so bit H is lost. Use the page's loop, which reads QH before each clock.

### How do I read 16 inputs from one Pico?

Wire the first register's QH to the second one's SER, keep SH/LD and CLK shared on GP0 and GP1, and run the loop for 16 bits. The Pico still uses three pins.

## More

- [74HC165 Shift Register reference](https://www.tinkered.ai/components/74hc165-shift-register.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the 74HC165 Shift Register on the Raspberry Pi Pico in the browser, with this wiring and code, free: https://www.tinkered.ai/components/74hc165-shift-register/raspberry-pi-pico