A card dispenser requires reliable and accurate performance across many different different environments and card swipe speeds; irrespective of the physical condition in the card. You can find three essential aspects 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 the input waveform to improve dynamic range;
(2) accurate peak detection and raw data decoding; and
(3)preventing noise inside the system from causing erroneous readings.
By using a PGA along with an ADC, the input waveform could be measured and scaled to increase the dynamic selection of the machine;which will allow a variety of input waveforms to be detected. This short article will also show what techniques may be used to accurately detect peaks inside the input waveform to see the fundamental information through the magnetic card.
The 1st essential component of card dispenser is definitely the automatic gain control (AGC), which automatically adjusts the amplitude of the input waveform to optimize the dynamic range of the machine. The amplitude in the waveform is very influenced by 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 will vary by over 25 dB across all swipe speeds. A fixed gain may be used to bring this voltage into a usable level, but to ensure the signal is in the optimum level whatsoever swipe speeds, AGC is actually a necessity. During the given swipe, a person will inadvertently change their swipe speed several times. As such, the gain in the circuit needs to be adjusted through the swipe to be certain any variations in signal amplitude are accounted for.
There are two essential components needed to implement AGC: an ADC as well as a PGA. In order to determine what gain needs to be used on the PGA at any time, we must be aware of current amplitude in our input waveform. The ADC could be used to monitor the input signal level and adjust the PGA if needed. When 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 a magnetic card signal are really pronounced, it can be hard to have an ADC to sample the input signal in a sufficient rate so that the amplitude from the peaks inside the waveform are accurately measured. To help lessen the stress around the ADC, a peak and hold circuit can be used to contain the amplitude of every peak. The 17dexbpky time at which the amplitude is sampled is not important, as long as the sampling and updating of the PGA occur regularly.
To be able to decode your data contained within the waveform, the peaks of your input waveform must be detected. This can be achieved in a variety of ways, each way having advantages and disadvantages. Constructing a basic peak detection circuit is pretty easy, but making a peak detector for magnetic card reader can be hard for several reasons:
1.The rate in the incoming peaks may differ from a couple of hundred bits per second to in excess of 10 kb/s, according to the swipe speed, card and card channel.
2.The amplitude of the peaks can vary greatly. This may be partially remedied by using AGC, but still should be considered for precise peak detection.
3.The peaks of your magnetic card waveform are pronounced, however the regions between each peak are often very flat – which could cause noise issues in comparator or differentiator based designs.