This application uses the myRIO-1900 to implement a lock-in amplifier in the FPGA. The application measures a modulated signal and a reference signal, which can also be generated with myRIO. The lock-in amplifier can measure very low level input signals, even if they are buried in noise or are smaller than myRIO’s 12-bit resolution. The lock-in amplifier includes a selectable high-pass filter to remove any input DC offset, and also includes a programmable output low pass filter that removes any noise beyond the frequencies of interest. The application is geared towards education and understanding the principles of a lock-in amplifier. It includes extensive documentation and instructions for building a circuit to measure heart rate by using an LED and photodiode amplifier to measure the amount of light absorbed through the blood vessels in a finger.
Lock-in Amplifier Accessory for myRIO
This accessory is the fastest way to get started with the Lock-In Amplifier for myRIO add-on. The board includes a red LED to generate modulated light, and a photodiode and signal conditioning circuitry to measure the received signal. This accessory can be used for a variety of measurements, such as determining your heart rate. If you place your finger between the LED and photodiode, the Lock-In Amplifier will pick up the small difference in absorbed light as blood pumps in and out of the capillaries in your fingertip. The add-on uses this information to calculate heart rate. You can order the board with the configuration that best suits your measurements:
- LED and photodiode soldered on the board as shown in the image
- Loose LED and photodiode so you can attach them to your own fixture
- SMA Connectors for the reference output and 5V input signal.
If you would like a board with SMA connectors configured for current input, or for orders outside the US, please contact us at firstname.lastname@example.org.