Reading hear rate with piezo sensor

Heart rate is one of many important physiological parameters. It can be an indicator of workout intensity, stress, and even decease. With heart rate information you can do many interesting signal processing experiments like detecting its variations, or even fuse with other physiological data. There are several ways of getting heart rate data. One well known method is by using LED and its light pass variations through finger (pulse-oxymetry). Ohhitch have tried to attache piezo sensor to finger and found out that it detects heart rate very well.

finger_piezo_sensor

Piezo sensor was connected to Arduino analog input which reads voltage differences due to blood flow pressure changes. This is enough to get reliable data. Simple Arduino code reads analog value and applies simple thresholding procedure which calculates heart rate in bpm.

Arduino Mega oscilloscope with TFT display

Oscilloscope is one of most important test devices in electronics. If your needs are not very high, you can go with any cheap or DIY scope. But in the end I would recommend getting standard bench oscilloscope. It saves time and eventually money. If you currently have low budget for purchasing scope, then take a look at this following scope project where vaupell builds it with Arduino Mega and TFT display.

Scope project is mostly glued out of two sources where one deals with Arduino scope functionality and another with TFT display. The end result looks great and serves the needs.

Arduino Shield for Battery Operated Sprinkler

This is a very different project that aims at creating an Arduino based shield for battery-operated sprinkler. Although the work on creating an Arduino based controller for the sprinkler is in development stage, this one is ready to buy shield. The shield is designed to work with battery-operated sprinkler waves. The valves inside utilize a latching solenoid, which just draws power when you open or close the valve, and does not draw power in the event that it stays in the same state. Therefore, they are very efficient and are ideal for battery operated controllers.

Moreover, the shield can also be stacked with other shield such as WiFi to provide web control. There’s an on-boost converter which helps in generating high voltage require to open or close the valve. An H-Bridge has also been made by using 4 MOSFET switches to generate voltage in both polarities (Ex: -9V and 9V). Overall an exciting application of both analog as well as digital electronics. If you are interested in the shield you can buy it or even make it yourself with the help of manual available on the project website.

Quick frequency counter with Arduino

Frequency is very important parameter of any signal. No matter if you are generating or synthesizing signals, you most likely need to measure its frequency. When signal frequency is bellow 40kHz and amplitude is near 5V then you can build frequency counter on Arduino with standard LCD screen. If measure signal is 5V (or 3.3V) level then you can feed it directly in to Arduino input. In other cases you need to use limiting circuit like amplifier or voltage divider. But this small project assumes that voltage is fed directly to microcontroller input.

frequency-meter-using-arduino

In this example signal comes to digital pin 12 where function pulseIn() counts number of pulses during specified time. Program itself is only few lines of code, and hardware is straight forward so putting it to work condition is only a matter of minutes.