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Tape Address Detector Subsystem

IP.com Disclosure Number: IPCOM000074016D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Schaefer, WC: AUTHOR [+2]

Abstract

This subsystem has an analog counter running independently of pulse width and pulse frequency, allowing the tape to run as slow or as fast as required. Absence detection makes the system insensitive to sporadic noise bursts. The detector also operates at the frequency that was last received, which forms an added noise rejection feature.

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Tape Address Detector Subsystem

This subsystem has an analog counter running independently of pulse width and pulse frequency, allowing the tape to run as slow or as fast as required. Absence detection makes the system insensitive to sporadic noise bursts. The detector also operates at the frequency that was last received, which forms an added noise rejection feature.

The subsystem consists of a tone burst generator, not shown, which is used to write address marks on a tape and a tone burst detector which is used to read these marks. The tone burst generator emits 55 milli-second bursts of 500 Hz which are recorded on one track of a magnetic tape by a tape recorder. The tape contains two tracks: one track contains audio messages which come from a person's voice through a microphone; the other track contains the 55 ms bursts which occur between the audio messages on the first track. These tone bursts are used to count the number of audio messages on the first track. During normal play operation, the tone bursts are 500 Hz. During fast playback operation, the tone burst frequency increases to 13KHz. Tone burst detector 10 serves to detect the bursts coming from the record track through a read head. An amplifier 12 and limiter circuits 14 and 16 serve to amplify the read head signal and square it up.

The analog counter consists of: a 20 mu s single-shot circuit 18, a sample and hold stairstep circuit 20, a Schmitt trigger circuit 22 and a voltage converter 24. The limits vary in frequency and width, depending on whether the input frequency to the detector is 500 Hz or 13 KHz. The 20 mu s single-shot circuit 18 dispenses the same amount of charge to a capacitor in the sample and hold stairstep circuit 20 for every pulse which comes along, regardless of the width and repetition frequency of the pulse. The stairstep voltage thus rises a fixed amount every time the single-shot circuit 18 turns off.

This voltage rises in a stairstep fashion. When it reaches the triggering level of the Schmitt trigger circuit 22, the Schmitt trigger changes state, causing the output of the voltage converter 24 to change state also. This causes the 40 ms single-shot circuit 26 to activate an inverter transistor in a circuit 28, essentially a pair of shorting switches, which resets the stairstep capaci...