A photoelectric circuit for reading punched data tape wherein the circuit compensates for variations in phototransistors and light emitting diodes, dust accumulation and degradation of the light emitting diodes by comparing the light transmitted through a punched section of the tape to the light transmitted through a solid section of the tape.

A scanning system having a laser and a motor for spinning an optical mirror arrangement for sensing indicia such as bar codes is capable of turning off the laser and the motor during periods of extended inactivity in order to minimize wear of these components and to reduce the use of electricity. Changes in the ambient light level adjacent to the scanning system which are typical of human motion are detected and are used to produce an electrical signal which can be used to turn the laser and the motor back on.

A method and apparatus for calibrating a bar code scanner. The bar code scanner contains circuitry including a programmable read-only memory (PROM) which stores data affecting the operation of other circuitry in the bar code scanner. The operation of the bar code scanner can be optimized by being monitored by an adjustment circuit under the control of a computer, the adjustment circuit producing signals which change the data stored in the PROM. Among the aspects of the bar code scanner which can be affected are optimization of the output signal, optimization of the signal which causes the bar code symbol to be illuminated, and response of the bar code scanner to the lack of a bar code symbol to read.

An optical scanning system comprises an optical scanner, a first circuit for generating a reference pulse and a second circuit for comparing a benchmark pulse scanned by the scanner to the reference pulse. The comparing circuit provides an indicating signal of one of a less than, a greater than and an equal to signals as a result of the comparison. There is a third circuit for adjusting sensitivity of the scanner based on the indicating signal. In one embodiment a visual indication is provided to distinguish between the less than, greater than and equal to signals so that a manual adjustment can be made to the scanner sensitivity. In another embodiment, automatic adjustments are made if a predetermined number of less than or greater than signals are provided before an equal to signal is provided by the comparing circuit.

A method of initializing an optical scanning system by centering a benchmark code in an electrically adjustable benchmark window, the benchmark code being scanned by the optical scanning system while being transported through a paper handling machine. The improvement comprises the steps of providing an encoder for timing the machine cycles of the paper handling machine as a plurality of documents are processed therethrough; conveying a document containing a benchmark code to be scanned past a scanning device of the optical scanning system; enabling a counter at the lead edge of the electrically adjustable benchmark window; incrementing the counter once for every two encoder pulses; disabling the counter when the scanning device detects the benchmark code; displaying the count of the counter in a LED display; and adjusting the location of the benchmark window so that the benchmark code is substantially centered in the benchmark window based on the count displayed on the LED display.