Paper-sheet-discriminator

Description: The circuit provides power to the drive motor when one or no sheets are fed, but interrupts motor power when two or more overlapping sheets pass through the optodetector slot. The optodetector can be either an H2aB Darlington interruptor module or an H23B matched emitter-detector pair. The output from the optodarlington is connected to a Schmitt trigger, which includes transistors Q1 and Q2 for noise immunity and to accommodate minor variations in paper opacity. When the Schmitt trigger is activated, gate current is supplied to the SC148D output device. The power supply for the detector and Schmitt trigger is a simple RC diode half-wave configuration, selected for its low cost (fewer diodes and no transformers) and minimal bulk. Although this supply is directly coupled to the power triac, this is limited by current drain considerations (50 mA DC for the gate drive alone). It should be noted that direct coupling of the Schmitt trigger to the output triacs is preferred, as RFI is virtually eliminated with the quasi-DC gate drive.

The described circuit is designed to control a drive motor based on the presence of sheets in a feeding mechanism. The primary function of the circuit is to ensure that the motor operates only when the appropriate number of sheets is detected, thereby preventing jams or misfeeds that could occur if multiple sheets are fed simultaneously.

The optodetector plays a crucial role in this mechanism. It detects the number of sheets passing through its slot and provides feedback to the control circuitry. The choice of either the H2aB Darlington interruptor module or the H23B matched emitter-detector pair allows for flexibility in component selection based on availability and specific application requirements.

The Schmitt trigger configuration, utilizing transistors Q1 and Q2, enhances the reliability of the signal by providing noise immunity. This is particularly important in environments where electrical noise may affect the performance of the circuit. The Schmitt trigger also compensates for variations in paper opacity, ensuring consistent operation regardless of the type of sheets being fed.

The output of the Schmitt trigger is connected to the SC148D output device, which is responsible for driving the motor. The use of a simple RC diode half-wave power supply for the detector and Schmitt trigger is a cost-effective solution that minimizes component count and space requirements. However, care must be taken regarding the current drain, as the gate drive for the triac requires a significant amount of current (50 mA DC).

To ensure optimal performance and reduce the risk of radio frequency interference (RFI), direct coupling of the Schmitt trigger to the output triacs is implemented. This design choice enhances the overall reliability of the circuit and ensures that the motor operates smoothly without unintended interruptions or noise issues.The circuit outputs power to the drive motor when one or no sheets are being fed, but interrupts motor power when two or more superimposed sheets pass through the optodetector slot. The optodetector can be either an H2aB darlington interruptor module or an H23B matched emitter -detector pair.

The output from the optodarlington is coupled to a Schmitt trigger, comprising transistors Ql and Q2 for noise immunity and minor paper opacity variation immunity. When the Schmitt is on, gate current is applied to the SC148D output device. The de power supply for the detector and Schmitt is a simple rc diode halfwave configuration chosen for its low cost (fewer diodes and no transformers) and minimum bulk. While such a supply is directly coupled to the power triac, this is precluded by current drain considerations (50 mA de for the gate drive alone).

Note that direct coupling of the Schmitt to the output triacs is preferred, since RFI is virtually eliminated with the quasi-de gate drive.