HX711 Detailed explanation of pin function specifications and circuit principle instructions
The HX711 is a precision 24-bit analog-to-digital converter (ADC) used primarily for weighing scales, load cells, and other applications requiring high-accuracy analog-to-digital conversion. It belongs to the HX series of ADCs produced by Holtek Semiconductor. Below, I will provide detailed specifications for the HX711, including pin functions, circuit principles, pinout, packaging, and an extensive FAQ section. The requested details will be organized as clearly as possible in response to your request.
HX711 Pinout & Functionality Overview:
Pinout (24-Pin Package) Pin Number Pin Name Pin Function 1 VDD Power Supply (+5V) 2 GND Ground (0V) 3 A- Input from load cell (negative) 4 A+ Input from load cell (positive) 5 B- Input from load cell (optional, second input channel) 6 B+ Input from load cell (optional, second input channel) 7 C- Input for control (optional for certain configurations) 8 C+ Input for control (optional for certain configurations) 9 VREF+ Reference voltage (positive) 10 VREF- Reference voltage (negative) 11 PD_SCK Serial Clock input for powering down the device 12 DOUT Digital output (data output pin) 13 SCK Serial clock input for data transmission 14 AVDD Analog power supply 15 AVSS Analog ground 16 VSTBY Standby pin for the HX711 (to enter power-saving mode) 17 CLK1 Clock input for ADC data conversion 18 CLK2 Clock input for ADC data conversion 19 REF Voltage reference for load cells or external analog inputs 20 INT Interrupt pin for signaling the completion of conversion 21 TRIGGER External trigger for specific modes and operations 22 TEST Test pin used for internal diagnostics 23 STBY1 Standby control 1 24 STBY2 Standby control 2Circuit Principle and Functionality:
The HX711 operates by converting the small differential voltage from a load cell into a 24-bit digital output that can be read by a microcontroller or processing unit. Here's an overview of the principle of operation:
Power Supply (VDD and GND): Powering the HX711 module is required for it to function. It operates on 5V and is referenced to ground (GND). Differential Inputs (A+ / A- / B+ / B-): These pins receive the analog signals from the load cells. The pins A+ and A- correspond to the positive and negative leads of one load cell (typically the main measurement channel), while B+ and B- are used for an additional differential input (for multi-channel applications). Reference Voltage (VREF+ / VREF-): The reference voltage is used to set the measurement range. By adjusting this voltage, you can calibrate the HX711 to measure different load cell outputs. Serial Clock Input (PDSCK / SCK): The PDSCK pin is used to put the HX711 into a power-down mode. The SCK pin is used to send clock pulses, signaling the HX711 to output data. Digital Output (DOUT): The DOUT pin outputs the converted digital data. Data is shifted out when the SCK pin is pulsed. Standby Pin (VSTBY): The VSTBY pin is used to enter a low-power standby mode when not in use.Pin Function FAQ (20 Frequently Asked Questions):
Q: What is the function of the A+ and A- pins on the HX711? A: These pins receive the analog signal from the load cell. A+ is the positive lead, while A- is the negative lead of the load cell.
Q: How do I set the reference voltage on the HX711? A: The reference voltage is set through the VREF+ and VREF- pins. You can connect these pins to an external reference or a fixed voltage source for calibration.
Q: Can I use both channels of the HX711? A: Yes, the HX711 supports two channels, labeled as A and B. You can use B+ and B- for a second load cell, though this is optional.
Q: What is the purpose of the SCK pin? A: The SCK pin is used to provide clock pulses that control the timing of data transfer from the HX711 to your microcontroller or processor.
Q: How do I wake up the HX711 from standby mode? A: To wake up the HX711, you need to send a clock pulse to the SCK pin or disable the standby mode by sending specific control signals via the VSTBY pin.
Q: What is the function of the DOUT pin? A: The DOUT pin is the digital output pin where the converted data is available for reading. It is used to transmit the digital result of the conversion.
Q: What is the PD_SCK pin used for? A: The PD_SCK pin is used for powering down the HX711, saving power when the device is not in use.
Q: Can I use a different reference voltage for each load cell? A: Yes, you can supply different reference voltages to VREF+ for each channel (A and B), depending on the design of your load cell system.
Q: How do I handle calibration of the HX711? A: Calibration is done by adjusting the reference voltage (VREF+ / VREF-) and fine-tuning the system's scale factor to match the output of the load cell under known weights.
Q: Does the HX711 support differential input? A: Yes, the HX711 supports differential input for high-accuracy measurements, with pins A+ and A- (main channel) and B+ and B- (optional second channel).
Q: What is the significance of the AVDD and AVSS pins? A: These pins provide the analog power supply and ground, respectively, and are critical for accurate conversion and stable operation of the HX711.
Q: Is it possible to use the HX711 without a load cell? A: While the HX711 can technically operate without a load cell, it will not function as intended without an analog input signal from a load cell or similar sensor.
Q: What is the maximum number of load cells I can connect to the HX711? A: The HX711 is designed to handle two load cells (one per channel). If more are required, additional HX711 modules are needed.
Q: How can I adjust the gain for the input channels? A: The gain is set internally for the two input channels. Channel A has a higher gain than channel B, typically selectable by the user during the calibration process.
Q: How accurate is the HX711 ADC conversion? A: The HX711 offers 24-bit resolution, making it highly accurate for small changes in weight. The accuracy can be affected by noise and the stability of the reference voltage.
Q: What is the typical power consumption of the HX711? A: The HX711 typically consumes about 1.5mA in active mode, which can be reduced further by using the standby feature.
Q: How can I ensure noise immunity with the HX711? A: To minimize noise, ensure proper grounding, use shielded cables for your load cells, and maintain stable reference voltages.
Q: Can the HX711 be used in industrial applications? A: Yes, with proper calibration and filtering, the HX711 is suitable for industrial and commercial weighing systems.
Q: Is there an interrupt feature in the HX711? A: Yes, the HX711 provides an interrupt pin (INT) that signals when a conversion is complete, allowing for efficient data handling.
Q: How do I calculate the weight from the HX711 output? A: To convert the digital output to weight, you need to calibrate the HX711 with a known weight and use the scale factor derived during this calibration.
These specifications and FAQs cover key aspects of the HX711 module, focusing on pin functions, circuit principles, and common issues encountered during use.
