A magnetic stirrer is an indispensable instrument in any laboratory setting. Commercially available stirrers are costly and have a defined life-span. The construction of a low-cost magnetic stirrer based on pulse width modulation is described. The design reported uses mainly recycled parts which results in a robust and efficient device at a very reasonable cost of ~US$17.50, which will be particularly attractive in developing countries. The project requires a multidisciplinary approach and can be utilized as a teaching exercise.