How to Use FMC920: Examples, Pinouts, and Specs

The FMC920 is a high-performance, low-power analog-to-digital converter (ADC) manufactured by Teltonika. Designed for precision data acquisition and signal processing, the FMC920 offers a flexible interface and supports multiple input channels, making it ideal for complex measurement systems. Its compact design and robust performance make it suitable for a wide range of applications, including industrial automation, medical instrumentation, and environmental monitoring.

• Data acquisition systems
• Signal processing in industrial automation
• Medical instrumentation for precise measurements
• Environmental monitoring and sensor interfacing
• Embedded systems requiring multi-channel ADC functionality

1. Power Supply: Connect the VCC pin to a 3.3 V or 5 V power source and the GND pin to the ground.
2. Analog Inputs: Connect the analog signals to the input channels (CH1–CH4). Ensure the input voltage does not exceed the specified range (0–5 V).
3. SPI Interface: Connect the SPI pins (SCLK, MISO, MOSI, and CS) to the corresponding pins on your microcontroller or processor.
4. Configuration: Use the SPI interface to configure the ADC settings, such as sampling rate and channel selection.

• Input Voltage Protection: Use a voltage divider or clamping diodes to ensure the input voltage remains within the 0–5 V range.
• Decoupling Capacitors: Place a 0.1 µF ceramic capacitor close to the VCC pin to reduce power supply noise.
• Grounding: Ensure a solid ground connection to minimize noise and improve signal integrity.
• SPI Communication: Use proper pull-up or pull-down resistors on the SPI lines if required by your microcontroller.

Below is an example of how to interface the FMC920 with an Arduino UNO using the SPI library:

#include <SPI.h>

// Define SPI pins for the FMC920
const int CS_PIN = 10; // Chip select pin for the ADC

void setup() {
  // Initialize serial communication for debugging
  Serial.begin(9600);

  // Set up SPI communication
  SPI.begin();
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH); // Set CS pin to inactive state

  Serial.println("FMC920 ADC Initialized");
}

void loop() {
  // Select the ADC by pulling CS low
  digitalWrite(CS_PIN, LOW);

  // Send a command to read from channel 1 (example command: 0x01)
  byte command = 0x01; // Replace with actual command for your application
  SPI.transfer(command);

  // Read the ADC data (12-bit result split into two bytes)
  byte highByte = SPI.transfer(0x00); // Read high byte
  byte lowByte = SPI.transfer(0x00);  // Read low byte

  // Combine the two bytes into a 12-bit result
  int adcValue = (highByte << 8) | lowByte;

  // Deselect the ADC by pulling CS high
  digitalWrite(CS_PIN, HIGH);

  // Print the ADC value to the serial monitor
  Serial.print("ADC Value: ");
  Serial.println(adcValue);

  delay(1000); // Wait for 1 second before the next reading
}

1. No Output or Incorrect Readings

   • Cause: Incorrect SPI connections or configuration.
   • Solution: Verify the SPI connections (SCLK, MISO, MOSI, and CS) and ensure the SPI settings (clock speed, mode) match the FMC920's requirements.

2. Noise in ADC Readings

   • Cause: Power supply noise or poor grounding.
   • Solution: Add decoupling capacitors near the VCC pin and ensure a solid ground connection.

3. Overvoltage on Input Channels

   • Cause: Input voltage exceeds the 0–5 V range.
   • Solution: Use a voltage divider or clamping diodes to protect the input channels.

4. SPI Communication Fails

   • Cause: Incorrect chip select (CS) handling.
   • Solution: Ensure the CS pin is pulled low before sending commands and pulled high after communication.

Q: Can the FMC920 operate at 3.3 V?
A: Yes, the FMC920 supports both 3.3 V and 5 V power supply levels.

Q: What is the maximum sampling rate of the FMC920?
A: The FMC920 supports a maximum sampling rate of 1 MSPS.

Q: How many channels can be used simultaneously?
A: The FMC920 has 4 input channels, but only one channel can be sampled at a time.

Q: Is the FMC920 compatible with Arduino boards?
A: Yes, the FMC920 can be interfaced with Arduino boards using the SPI interface.