Led's: Convenient, inexpensive sources for visual experimentation—a modified circuit

An improved circuit for control of LED luminance

“…This circuit provides a more stable output than driver circuits designed without feedback, in which LED luminance may drift with temperature. In our circuit, the LED is referenced to ground, which has two advantages over designs without ground referencing (e.g., Alden, 1983;Mayzner & Dolan, 1978;Nygaard & Frumkes, 1982): (1) The LED may be connected to its input by a shielded coaxial cable, eliminating possible shock hazard to subjects and preventing the output of electrical source artifacts; (2) the circuit may be used to drive one of several LEDs through a matrix switching array (see Figure 3). Figure 1 shows the circuit.…”