Scott W Harden writes:
I re-vamped my DIY ECG project. This new project is fully documented and uses extremely common and cheap parts, all of which could be purchased at RadioShack. It serves at both an ECG *and* a pulse oximeter, depending on which leads are attached. It uses a single chip (LM324, a quad operational amplifier) with a virtual ground to eliminate the need for a negative voltage. As a pulse oximeter with a 12V supply it outputs clean 10V swings when pulses occur. It’s intentionally unsophisticated, and made to be easy to replicate by anyone interested in electronics. Although you could view its output on an oscilloscope, it’s designed to be output into a PC sound card for recording (if attenuated to microphone levels). I even describe how to spectrally process the data on the computer to clean it up, downsample it, and graph it in Excel or with a Python script.
Simple DIY ECG + Pulse Oximeter - [Link]
Designing a simple and yet functional Line Follower Robot (LFR) is always a fascinating and challenging subject to be learned, the LFR actually could be implemented in many ways start from a simple two transistors to a sophisticated PID (Proportional, Integrate and Differential) which take advantage of the programmable feature of microcontroller to calculate the PID equation to successfully navigate the black track line on a white background surface.
The LM324 Quad Op-Amp Line Follower Robot with Pulse Width Modulation - [Link]
This project is a line follower robot built around the LM324 quad op-amp. It uses two of the amp circuits in a triangle generator. The other two amps operate as hi/lo comparators. They compare the voltage across the photoresistors with the triangle wave, and thus determine if the robot is moving over the line or the whitespace. [via]
Op-amp Line Follower Robot with PWM Motor Control - [Link]
This circuit is a fan controller which is using the pulse width modulation (PWM) method. It is tiny (33.78mm x 54.76mm) and easy to build. Functions of the circuit parts are listed below;
PWM Fan Controller by LM2902N or LM324N - [Link]
VU (Voltage Unit) meters are often included in analog audio equipments to display a signal level in Visual Units. We are building a mono input VU meter in this project. You can build one more to use them in stereo mode. Input sensitivity is about 1 Volt rms, up to +6dB. You can adjust the amplitude of the input by using the multiturn 50k linear potentiometer (POT1).
10 LED VU Meter Project by LM3915 and LM324 - [Link]