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Digital (tape) Counter

Tape counters are individual machine specific and can only be used as a rough guide. And are only provided as such. Even counters displaying ‘real time’ aren’t very accurate and don’t conform to any standard.

Since there are still tape records 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 in 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 subdivided into a number of alternate reflecting and non-reflecting segments. The two optoisolators are positioned above the disc in such a way that 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 segments. 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

Digital (tape) Counter.

An optoisolator connects input and output sides with a beam of light modulated by the input current. It transforms a useful input signal into light, sends it across the dielectric channel, captures light on the output side, and transforms it back into an electric signal.

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