# Project - Binary Display
In this project, we’re going to create a fun binary counter using the 74HC595 shift register and 8 LEDs. The LEDs will light up to display numbers in binary format, counting from 0 to 255. Not only will this project teach you how to expand your output capabilities with the 74HC595, but it will also give you hands-on experience with bitwise operations and serial data communication. Let’s dive in and light up those LEDs!
## Diagram
| 74HC595 | Connection |
| -------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Pin 8 | GND |
| Pin 10 | VCC |
| Pin 11 | Clock to Arduino IO5 |
| Pin 12 | Latch to Arduino IO4 |
| Pin 13 | GND |
| Pin 14 | Data to Arduino IO3 |
| Pin 16 | VCC 3.3V |
| Pin 15
Pin 1 to 7 | Connect the LED’s positive leg (long leg) to the output pin of the 74HC595. Connect the LED’s negative leg (short leg) to one end of a 220Ω resistor, and connect the other end of the resistor to GND.
| ## Basic Code Let’s take a look at the simplest code to turn on an LED. ```cpp const int dataPin = 3; // Serial Data In (74HC595 Pin14) const int latchPin = 4; // Latch (74HC595 Pin12) const int clockPin = 5; // Clock (74HC595 Pin11) void setup() { pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); digitalWrite(latchPin, LOW); // Prepare to shift shiftOut(dataPin, clockPin, MSBFIRST, 0b11000000); // MSBFIRST order digitalWrite(latchPin, HIGH); // Latch the data } void loop() { } ``` ```cpp pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); ``` The 74HC595 requires three pins—**Latch**, **Data**, and **Clock**—to be connected to the MCU’s GPIO. These GPIO pins on the MCU must be set to **output mode**, as the data flows from the MCU to the 74HC595. ```cpp digitalWrite(latchPin, LOW); // Prepare to shift ``` The **latch pin** is used to control when the data shifted into the shift register is sent to the output pins (Q0–Q7). Setting the latch pin LOW ensures that the data being shifted into the shift register does **not immediately affect the output pins (Q0–Q7)**. This prevents intermediate or incomplete data from appearing on the outputs during the shift operation. ```cpp shiftOut(dataPin, clockPin, MSBFIRST, 0b11000000); ``` This line is using the shiftOut() function to send a **byte** of data (8 Bits) to a shift register **74HC595**. - dataPin: This is the pin connected from MCU to the **DATA pin (Pin 14) of the 74HC595**. It is where the binary data is sent from MCU, one bit at a time. - - clockPin: This is the pin connected to the **CLOCK ** pin (Pin 11) of the 74HC595**. Each time this pin is pulsed (LOW → HIGH → LOW), the shift register shifts in a bit from the dataPin. - - MSBFIRST: This tells the shiftOut function to send the **Most Significant Bit (MSB)** first.It means the data is shifted starting with the **highest-value bit** (leftmost bit in binary). In the case of 0b10101010: - • **MSB (Most Significant Bit)** = The leftmost bit (1 in this case). When using MSBFIRST, the bits are sent in the following order: **1 → 1 → 0 → 0 → 0 → 0 → 0 → 0**. The first 1 will be sent to **Q7** of the 74HC595, and the second 1 will be sent to **Q6**. The LEDs connected to **Q7** and **Q6** will turn on.  - **LSB (Least Significant Bit)** = The rightmost bit (0 in this case). When using LSBFIRST, the bits are sent in the following order: **0 → 0 → 0 → 0 → 0 → 0 → 1 → 1**. Since the two 1s are sent last, they will be assigned to **Q1** and **Q0**. The LEDs connected to **Q1** and **Q0** will turn on.  ```cpp digitalWrite(latchPin, HIGH); // Latch the data ``` After all 8 bits have been shifted in, setting the latch pin HIGH transfers the internal data to the output pins (Q0–Q7). This ensures that the outputs are updated all at once, avoiding glitches or incomplete data appearing on the pins. #### **Try it Yourself** - Try changing from **MSBFIRST** to **LSBFIRST** and observe the result. - Try converting the binary value **0b11000000** to its decimal equivalent (128). ## Binary Display Code A single **74HC595** shift register can control up to 8 LEDs. Each LED can be turned on or off, which is ideal for representing a binary digit. With 8 LEDs, you can represent a range of decimal numbers from **0 to 255**. Let’s create a simple binary counter that counts from **0 to 255** and displays the numbers using the LEDs connected to the shift register.  ```cpp const int dataPin = 3; // Serial Data In (74HC595 Pin14) const int latchPin = 4; // Latch (74HC595 Pin12) const int clockPin = 5; // Clock (74HC595 Pin11) void setup() { pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); } void loop() { for (int i = 0; i <= 255; i++) { // Shift out the binary representation of the number 'i' (0-255) digitalWrite(latchPin, LOW); // Prepare to shift data shiftOut(dataPin, clockPin, MSBFIRST, i); // Send the data digitalWrite(latchPin, HIGH); // Latch the data to the output pins (LEDs) delay(1000); // Wait for a second to observe the change } } ``` # Limitation ### Voltage Limits **74HC595** has a maximum supply voltage range of **2V to 6V**, so it can’t handle voltages outside of this range. If the **74HC595** shift register is powered by **3.3V**, the output voltage for each pin (Q0 to Q7) will also be **3.3V** when the output is high. ## Current Limits The **74HC595** can source or sink a limited amount of current (typically around 6–8 mA per pin). It can only directly connect normal LED. You cannot connect high-current devices like Large LEDs, motors, or relays directly to the outputs. If the **external devices (LED, Motor, Relay) requires a large voltage** (like **12V or 24V**) and a **large current**, using an **N-channel MOSFET** is a great solution. The **MOSFET** will act as a **switch**, allowing the low-power signal from the **74HC595** to control the higher voltage and current needed for the LED.
Pin 1 to 7 | Connect the LED’s positive leg (long leg) to the output pin of the 74HC595. Connect the LED’s negative leg (short leg) to one end of a 220Ω resistor, and connect the other end of the resistor to GND.
| ## Basic Code Let’s take a look at the simplest code to turn on an LED. ```cpp const int dataPin = 3; // Serial Data In (74HC595 Pin14) const int latchPin = 4; // Latch (74HC595 Pin12) const int clockPin = 5; // Clock (74HC595 Pin11) void setup() { pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); digitalWrite(latchPin, LOW); // Prepare to shift shiftOut(dataPin, clockPin, MSBFIRST, 0b11000000); // MSBFIRST order digitalWrite(latchPin, HIGH); // Latch the data } void loop() { } ``` ```cpp pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); ``` The 74HC595 requires three pins—**Latch**, **Data**, and **Clock**—to be connected to the MCU’s GPIO. These GPIO pins on the MCU must be set to **output mode**, as the data flows from the MCU to the 74HC595. ```cpp digitalWrite(latchPin, LOW); // Prepare to shift ``` The **latch pin** is used to control when the data shifted into the shift register is sent to the output pins (Q0–Q7). Setting the latch pin LOW ensures that the data being shifted into the shift register does **not immediately affect the output pins (Q0–Q7)**. This prevents intermediate or incomplete data from appearing on the outputs during the shift operation. ```cpp shiftOut(dataPin, clockPin, MSBFIRST, 0b11000000); ``` This line is using the shiftOut() function to send a **byte** of data (8 Bits) to a shift register **74HC595**. - dataPin: This is the pin connected from MCU to the **DATA pin (Pin 14) of the 74HC595**. It is where the binary data is sent from MCU, one bit at a time. - - clockPin: This is the pin connected to the **CLOCK ** pin (Pin 11) of the 74HC595**. Each time this pin is pulsed (LOW → HIGH → LOW), the shift register shifts in a bit from the dataPin. - - MSBFIRST: This tells the shiftOut function to send the **Most Significant Bit (MSB)** first.It means the data is shifted starting with the **highest-value bit** (leftmost bit in binary). In the case of 0b10101010: - • **MSB (Most Significant Bit)** = The leftmost bit (1 in this case). When using MSBFIRST, the bits are sent in the following order: **1 → 1 → 0 → 0 → 0 → 0 → 0 → 0**. The first 1 will be sent to **Q7** of the 74HC595, and the second 1 will be sent to **Q6**. The LEDs connected to **Q7** and **Q6** will turn on.  - **LSB (Least Significant Bit)** = The rightmost bit (0 in this case). When using LSBFIRST, the bits are sent in the following order: **0 → 0 → 0 → 0 → 0 → 0 → 1 → 1**. Since the two 1s are sent last, they will be assigned to **Q1** and **Q0**. The LEDs connected to **Q1** and **Q0** will turn on.  ```cpp digitalWrite(latchPin, HIGH); // Latch the data ``` After all 8 bits have been shifted in, setting the latch pin HIGH transfers the internal data to the output pins (Q0–Q7). This ensures that the outputs are updated all at once, avoiding glitches or incomplete data appearing on the pins. #### **Try it Yourself** - Try changing from **MSBFIRST** to **LSBFIRST** and observe the result. - Try converting the binary value **0b11000000** to its decimal equivalent (128). ## Binary Display Code A single **74HC595** shift register can control up to 8 LEDs. Each LED can be turned on or off, which is ideal for representing a binary digit. With 8 LEDs, you can represent a range of decimal numbers from **0 to 255**. Let’s create a simple binary counter that counts from **0 to 255** and displays the numbers using the LEDs connected to the shift register.  ```cpp const int dataPin = 3; // Serial Data In (74HC595 Pin14) const int latchPin = 4; // Latch (74HC595 Pin12) const int clockPin = 5; // Clock (74HC595 Pin11) void setup() { pinMode(dataPin, OUTPUT); pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); } void loop() { for (int i = 0; i <= 255; i++) { // Shift out the binary representation of the number 'i' (0-255) digitalWrite(latchPin, LOW); // Prepare to shift data shiftOut(dataPin, clockPin, MSBFIRST, i); // Send the data digitalWrite(latchPin, HIGH); // Latch the data to the output pins (LEDs) delay(1000); // Wait for a second to observe the change } } ``` # Limitation ### Voltage Limits **74HC595** has a maximum supply voltage range of **2V to 6V**, so it can’t handle voltages outside of this range. If the **74HC595** shift register is powered by **3.3V**, the output voltage for each pin (Q0 to Q7) will also be **3.3V** when the output is high. ## Current Limits The **74HC595** can source or sink a limited amount of current (typically around 6–8 mA per pin). It can only directly connect normal LED. You cannot connect high-current devices like Large LEDs, motors, or relays directly to the outputs. If the **external devices (LED, Motor, Relay) requires a large voltage** (like **12V or 24V**) and a **large current**, using an **N-channel MOSFET** is a great solution. The **MOSFET** will act as a **switch**, allowing the low-power signal from the **74HC595** to control the higher voltage and current needed for the LED.
