LED matrix displays provide flexibility to display text, graphics, animations, and video, and therefore, they have become a popular mean of displaying information these days. You can see them at gas stations displaying the gas prices, or in the public places displaying information, and alongside highways displaying advertisements on large dot matrix panels. This project is about constructing a mono-color LED matrix display board that consists 320 LEDs arranged in 8 rows and 40 columns. The heart of this project is PIC16F1847 microcontroller which receives data from a PC through a serial port (or USB using an USB-UART interface), and display on the LED matrix with the help of five 74HC595 shift registers.

8x40 LED Matrix Display

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Pulse Width Modulation (PWM) is a digital method of delivering a varying amount of power to a load, and hence can be used to control the brightness of an LED or speed of a DC motor. Controlling the power, we will make this tutorial colorful using a Red Green Blue (RGB) LED. Each segment (lead) of an RGB-LED will get a PWM signal via RgbLed class allowing us to illuminate the RGB-LED with any color defined by RGB. This class can also generate random colors. Using the RgbLed class, some standard colors can also be sent to a RGB-LED.

RGB-LED illuminating a purple color

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In Part 1 of this article, we briefly discussed about the principle of Photoplethysmography (PPG) and its applications in retrieving vital information about the cardiovascular system. The Easy Pulse sensor allows you to measure the pulse rate from fingertip using the transmission mode PPG. The Easy Pulse Version 1.1 uses the HRM-2511-E sensor that fits comfortably onto fingertip. Inside the sensor there is an IR LED that illuminates the finger from one side. A photodetector placed on the opposite side and facing towards the IR LED detects the transmitted light through the finger. The little variations in the transmitted light intensity are synchronous with blood volume changes and hence with the pumping action of the heart. The on-board electronics filters out the noise from the PPG signal and amplifies the signal so that it is readable by a microcontroller. In this part, we continue our discussion of Easy Pulse Version 1.1 and analyze the output signals at various stages of instrumentation.

Easy Pulse sensor (Version 1.1)

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