A magnetic card reader requires reliable and accurate performance across a number of different environments and card swipe speeds; whatever the health from the card. You will find three essential factors of a magnetic card that really must be implemented to guarantee this performance:
(1) automatic gain control (AGC) to automatically adjust the amplitude of the input waveform to optimize dynamic range;
(2) accurate peak detection and raw data decoding; and
(3)preventing noise inside the system from causing erroneous readings.
Utilizing a PGA along with an ADC, the input waveform could be measured and scaled to optimize the dynamic selection of the program;that will allow a variety of input waveforms to be detected. This short article will also show what techniques enables you to accurately detect peaks inside the input waveform to read through the main information in the magnetic card.
The initial essential aspect of card dispenser is the automatic gain control (AGC), which automatically adjusts the amplitude of the input waveform to maximize the dynamic selection of the program. The amplitude of your waveform is tremendously reliant 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 may vary by over 25 dB across all swipe speeds. A fixed gain can be used to bring this voltage to a usable level, but so that the signal reaches the optimum level by any means swipe speeds, AGC is really a necessity. During a given swipe, a user will inadvertently change their swipe speed several times. As such, the gain from the circuit must be adjusted through the swipe to make sure any alterations in signal amplitude are included.
There are 2 essential components necessary to implement AGC: an ADC as well as a PGA. So that you can determine what gain should be placed on the PGA at any time, we need to know the current amplitude of our input waveform. The ADC may be used to monitor the input signal level and adjust the PGA as required. If the input signal passes below a set minimum threshold, the gain is increased. In the event 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 extremely pronounced, it can be difficult for an ADC to sample the input signal at the sufficient rate to ensure the amplitude of your peaks inside the waveform are accurately measured. To help lessen the stress around the ADC, a peak and hold circuit can be used to retain the amplitude for each peak. The 17dexbpky time in which the amplitude is sampled is irrelevant, provided that the sampling and updating of the PGA occur regularly.
So that you can decode the info contained in the waveform, the peaks of the input waveform has to be detected. This can be accomplished in a variety of ways, each way having positives and negatives. Constructing a fundamental peak detection circuit is fairly easy, but making a peak detector for TTL magnetic card reader can be challenging for a lot of reasons:
1.The velocity of your incoming peaks may vary any where 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 the peaks may differ greatly. This could be partially remedied by using AGC, yet still should be considered for precise peak detection.
3.The peaks of the magnetic card waveform are pronounced, however the regions in between each peak can be extremely flat – which may cause noise issues in comparator or differentiator based designs.