Manual bar code scanner with improved reliability

DETAILED DESCRIPTION The present invention overcomes the deficiencies in the art by providing a manual bar code scanner that scans the bar code multiple times in one pass.
This is accomplished by providing three sensors adjacent to each other such that, as the scanner is scanned over the bar code, the bar code is read three times.
Specifically, the invention consists of a bar code scanner having preferably three light sensors with corresponding light sources for illuminating the bar code.
In the preferred embodiment, the sensor diodes are spaced side-by-side approximately 2 mm apart.
The same bar code is thus read by all three sensors in series as the bar code is manually scanned one time.
Errors in the reading of the bar code are eliminated by a bit-wise majority voting scheme, which is able to correct a one-time read error in any single bit.
Three light sources which act as source of reflected light for their corresponding sensors are modulated at 100 kHz.
This has an effect similar to a chopper circuit.
Thus, reflected light sensed at the sensors is much higher frequency than the bar code signal itself.
As a result, the reflected light signal at the sensor can be easily amplified and demodulated as a high frequency AC signal.
Also, interference light such as florescent light will not interfere with reflected light signal, because reflected signal will be band pass filtered to filter out any interfering signals.
In the preferred embodiment, the bar code signal is typically a relatively low frequency (<3 Khz) signal when the user manually scans over it.
The light source operates as a modulator to generate a high frequency (about 100 kHz) AC signal for ease of signal processing in the receiver.
Thus, the novel aspects of the present invention are the modulation of the light sources at a high frequency and synchronous demodulation, bit-wise majority vote to correct read errors and the side-by-side placement of the light source/light sensor pairs to enable multiple reads per pass.