This circuit displays the content of a digital data storage tape through LEDs. The LEDs are labeled as:
- - data leader (the pilot tone at the beginning of every digital data group)
- - tape empty (no data recorded)
- - data
The capability to determine which part of the tape is empty and which part has a recorded data can help accelerate your work of looking for a certain program.
The circuit uses a tone decoder IC 567 and a timer IC 555. The 567 IC decodes the pilot tone of each recorded program. The tone frequency to which this tone decoder
reacts must be set with potentiometer P1. To do this, play a cassette with a recorded data and within the first 2 to 10 seconds try to adjust P1 so that LED D1 lights up. If you did
not get it at the first try, rewind the tape and start again from the beginning.
LED D2 lights up when the tape is empty or when the playback is between two programs at the moment. When a recorded data is detected, LED D3 lights up.
The input of the circuit is connected to the output of the cassette recorder. The signal from the tape reaches the inputs of the tone decoder 567 and the timer 555
simultaneously through capacitor C1. One of three things may possibly happen:
- First. No signal. The tone decoder 567 outputs a logic 1 (high) and the timer 555 outputs a logic 0 (low). IC 74145 activates decimal output 2. LED D2 lights up.
- Second. Leader Signal. IC 567 outputs a logic 0 (low). Timer 555 outputs logic 0 (low). IC74145 activates decimal output 1. LED D1 lights up.
- Third. Data signal. IC 567 outputs a logic 1 (high). Timer 555 outputs a logic 1 (high). IC 74145 activates decimal output 3. LED D3 lights up.
Electronic Circuits volume 1.0 - Circuit Nr. 75
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
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