A passport reader requires reliable and accurate performance across various different environments and card swipe speeds; irrespective of the wellbeing in the card. You can find three essential components of a magnetic card that really must be implemented to make sure this performance:
(1) automatic gain control (AGC) to automatically adjust the amplitude of the input waveform to increase dynamic range;
(2) accurate peak detection and raw data decoding; and
(3)preventing noise in the system from causing erroneous readings.
Using a PGA along with an ADC, the input waveform can be measured and scaled to optimize the dynamic array of the program;which can allow a variety of input waveforms being detected. This post will also show what techniques could be used to accurately detect peaks in the input waveform to see the primary information from your magnetic card.
The initial essential aspect of card dispenser is definitely the automatic gain control (AGC), which automatically adjusts the amplitude in the input waveform to increase the dynamic range of the device. The amplitude from the waveform is very dependent on the credit card swipe speed. Faster swipe speeds produce waveforms with peaks of greater amplitude, and slower swipe speeds produce waveforms with peaks of smaller amplitude. The voltage created by the magnetic read head is small, but could vary by more than 25 dB across all swipe speeds. A set gain could be used to bring this voltage to a usable level, but to be sure the signal is in the optimum level by any means swipe speeds, AGC is actually a necessity. In a given swipe, an individual will inadvertently change their swipe speed many times. Therefore, the gain in the circuit should be adjusted through the swipe to be certain any variations in signal amplitude are accounted for.
The two main essential components expected to implement AGC: an ADC along with a PGA. To be able to know what gain ought to be put on the PGA at any time, we must are aware of the current amplitude of our input waveform. The ADC may be used to monitor the input signal level and adjust the PGA when needed. If the input signal passes below a set minimum threshold, the gain is increased. If the input signal passes above a set maximum threshold and approaches saturation, the gain is decreased.
Ever since the peaks of the magnetic card signal are really pronounced, it can be hard to have an ADC to sample the input signal with a high enough rate so that the amplitude of the peaks inside the waveform are accurately measured. To help lessen the load around the ADC, a peak and hold circuit enables you to hold the amplitude of every peak. The 17dexbpky time in which the amplitude is sampled is irrelevant, provided that the sampling and updating of your PGA occur regularly.
As a way to decode the data contained in the waveform, the peaks from the input waveform should be detected. You can do this in a variety of ways, each way having advantages and disadvantages. Constructing a fundamental peak detection circuit is fairly easy, but building a peak detector for magnetic stripe card reader can be challenging for several reasons:
1.The velocity of the incoming peaks can differ from a couple of hundred bits per second to over 10 kb/s, dependant upon the swipe speed, card and card channel.
2.The amplitude of your peaks may vary greatly. This may be partially remedied by using AGC, yet still needs to be considered for precise peak detection.
3.The peaks in the magnetic card waveform are pronounced, but the regions between each peak can be quite flat - which can cause noise issues in comparator or differentiator based designs.