One way to measure the distance is to use ultrasonic transducer which is cheap and robust. Paoson Woodwork constantly needs to measure distances inside room while installing furniture or doing repair work. So he came up with idea of building an universal distance meter which would measure distances in all four directions at once.
He put electronics in to his custom made plywood enclosure where he made openings for sr04 ultrasonic transducers. He put an LCD in front, along with two buttons for unit selection and function. Additionally there is a bubble level tube included to keep things straight when hanging on the wall. All you have to do is to hang the meter on the wall and it displays the distance on LCD for in all four directions. It can display the area of wall with a single button press. There are other programs available along with area and distance. These are Rel – to measure relative distance, Total – to measure total distance between two opposing surfaces.
When you are harvesting solar or wind energy, you want to take most of it. For this you need efficient power converter which would take raw energy and convert it to proper voltage level for charging your batteries or powering electronics. Soldernerd have build an Arduino shield dedicated for charging lead acid battery. He used a solar panel with voltage output around 17V which had to be converted to 14V for lead battery.
This obviously required step down (buck) DC to DC converter which takes 17V – 18V from solar panel and converts it to 12V – 14V as efficient as possible. Microcontroller takes care of generating PWM signal which automatically adjusts to maintain output voltage level. Charger is capable to protect battery from overcharging when voltage of battery reaches 14V. Charger is capable to drive 30W power to the battery.
Rui Santos have compiled a list of useful Arduino shields. This is great source if you are looking for ideas for your next project or simply want to try something new.
He describes each shield along with eBay link where to purchase. He posts only 25 shields while there are hundreds of them. If you will dig deeper, probably you’ll find a shield for any purpose you may think.
Photoplethysmography (PPG) sometimes called pulse oximetry is on of the easiest ways to get heart rate information. With a little more analyze and signal processing it is possible to extract even more information related to your heart condition like arrhythmia. But first lets focus on how to acquire PPG signals with the things you might have lying around. SteveQuinn have built a PPG device around Arduino Mega2560, 128×160 TFT LCD, and several passives.
The measuring of PPG lies on blood perfusion to the dermis and subcutaneous tissue of the skin. Every cardiac cycle pumps blood to peripheral organs and this flow change can be measured with simple optical method – LED and photo diode. There are two ways of measuring PPG waveform – transmissive and reflective. Transmissive method seems to give better results this is why it was selected for this project. He built a simple finger clamp out of coat hanger where he fixed LED and photo diode. There are many small things to take care of, because signals are very small and susceptible to noise. For instance LED driving current has to be constant, power supply has to be clean, proper component selection plays also a significant role.