Circuit Lake

Electronic Project and Circuit Collection

AVR Thermistor Respiratory Monitor

01/11/2013 Category: AVR, Display, Measurement, Monitoring

The purpose of the project is to build a low-cost, easy-to-use device to monitor the breathing of patients. It was designed for low-resource environments. This AtMega1284-based project can calculates a patient’s breathing rate by detecting changes in temperature when the patient breathes through a mask.

The project uses AtMega1284p microcontroller as main controller. Thermistors are used as sensor to detect temperature difference when human breathes. As we know, resistance over the thermistor drops when it’s surrounding temperature increases, and goes back down when the temperature decreases. By placing thermistors as voltage divider, the temperature change will produce different voltage. This voltage changing then read by microcontroller’s ADC for more processing.

Low cost Respiratory Monitor

For easy monitoring, the project is equipped with LCD display to measure breathing rate in breaths/minute. This allows whoever is monitoring the patient to see if the patient is breathing too fast or too slowly. In order to reduce power usage, the LCD only receives power when the user presses the display button, which reduces the load on the battery.

The device has an alarm through a piezoelectric speaker which goes off when the patient stops breathing. It also has low-battery indicator signal when the battery powering the device reaches a threshold voltage.