Since there are still tape records about that have no mechanical tape counter, the circuit shown here offers an excellent, electronic add-on for these. It can, of course, also be used to replace a mechanical counter.
Furthermore, it can be used for other applications, for instance, as the hoist-height indicator for a model building crane, or for indicating the position of a chisel on a lathe.
The input of the circuit is formed by two optoisolators. The sequence of the pulse signals provided by these isolators depends on the direction into which a coding disc turns. The NAND gates following the isolators produce from those signals an up/down counter IC3 to register the position irrespective of the direction of rotation. The position is made visible via a decoder on a seven-segment display. The number of digits the counter provides can be extended by adding more counter/decoder/display stages to the extension terminals, pc1-pc4. In the same way that IC5, LD2 is connected to IC3.
The optical input signals are provided by a
coding disc that is sub-divided into a number of alternate reflecting and non-reflecting segments. The two optoisolators are positioned above the disc in such a way the when one is directly above a segment, the other is exactly above the line dividing two segments.It is, of course, possible to use a light barrier and a coding disc that has alternate transparent and opaque segment. Two LEDs and a pair of phototransistors can also be used.
The power supply is a 5 V regulated type that can deliver 250 mA. For each additional counter stage, 100 mA should be added to that figure.
Digital (tape) Counter.