0, IC! - using photodiodes

Light-sensitive devices are used in all kinds of fascinating applications: light-meters, cybernetic models, movement sensors — even optical communication links. We get the distinct impression, however, that many circuits are developed by means of enthusiastic trial-and-error — with little regard for basic principles. This can be great fun, admittedly: the result tends to perform in unexpectedly spectacular ways! We don"t really like printing "theoretical" or "educational" articles. In this case, however, some back- ground information seems long overdue. Furthermore, we have two practical circuits to offer: a light gate and a distance meter. 3 0, I C! using photodiodes 0, IC! elektor march 1983 Figure 1. A photodiode can be considered as a cur- rent source that is con- trolled by the light that falls onto it. The photo- current flows from cathode to anode. Figure 2. A photodiode can be used in two ways. The voltage across the diode can be measured directly (2a); alternatively, ...