A passport reader requires reliable and accurate performance across many different different environments and card swipe speeds; regardless of the physical condition in the card. You will find three essential components of a magnetic card that need to be implemented in order to ensure this performance:
(1) automatic gain control (AGC) to automatically adjust the amplitude of your input waveform to maximize dynamic range;
(2) accurate peak detection and raw data decoding; and
(3)preventing noise from the system from causing erroneous readings.
Employing a PGA along with an ADC, the input waveform might be measured and scaled to optimize the dynamic variety of the machine;which can allow a variety of input waveforms to become detected. This short article will also show what techniques could be used to accurately detect peaks within the input waveform to see the main information in the magnetic card.
The 1st essential element of passport scanner is the automatic gain control (AGC), which automatically adjusts the amplitude of your input waveform to increase the dynamic array of the machine. The amplitude in the waveform is very determined by the 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 may vary by more than 25 dB across all swipe speeds. A set gain could be used to bring this voltage to your usable level, but to guarantee the signal reaches the optimum level at all swipe speeds, AGC is a necessity. During a given swipe, an end user will inadvertently change their swipe speed a few times. As a result, the gain from the circuit ought to be adjusted during the entire swipe to be sure any changes in signal amplitude are made up.
The two main essential components needed to implement AGC: an ADC and a PGA. As a way to really know what gain must be used on the PGA at any given time, we should know the current amplitude of our own input waveform. The ADC enables you to monitor the input signal level and adjust the PGA as required. When the input signal passes below a set minimum threshold, the gain is increased. When the input signal passes above a set maximum threshold and approaches saturation, the gain is decreased.
Because the peaks of your magnetic card signal are really pronounced, it can be hard for an ADC to sample the input signal at the sufficient rate to ensure the amplitude in the peaks within the waveform are accurately measured. To help reduce the load on the ADC, a peak and hold circuit could be used to retain the amplitude of each peak. The 17dexbpky time in which the amplitude is sampled is irrelevant, as long as the sampling and updating from the PGA occur regularly.
In order to decode your data contained within the waveform, the peaks from the input waveform should be detected. You can do this in numerous ways, each way having benefits and drawbacks. Constructing a basic peak detection circuit is comparatively easy, but developing a peak detector for magnetic card reader can be challenging for a number of reasons:
1.The speed of the incoming peaks can differ anywhere from a few hundred bits per second to over 10 kb/s, according to the swipe speed, card and card channel.
2.The amplitude from the peaks may vary greatly. This may be partially remedied with the aid of AGC, but nonetheless needs to be considered for precise peak detection.
3.The peaks in the magnetic card waveform are pronounced, although the regions in between each peak are often very flat – which can cause noise issues in comparator or differentiator based designs.