TTL Magnetic Card Reader – Four Matters You Must Contemplate When Choosing
March 18, 2017
A card dispenser requires reliable and accurate performance across a variety of different environments and card swipe speeds; whatever the physical condition of the card. There are three essential elements of a magnetic card that really must be implemented to guarantee this performance:
(1) automatic gain control (AGC) to automatically adjust the amplitude from the input waveform to improve dynamic range;
(2) accurate peak detection and raw data decoding; and
(3)preventing noise within the system from causing erroneous readings.
By using a PGA along with an ADC, the input waveform might be measured and scaled to increase the dynamic range of the system;that can allow an array of input waveforms to be detected. This short article will also show what techniques enables you to accurately detect peaks in the input waveform to read through the essential information in the magnetic card.
The first essential element of card dispenser is the automatic gain control (AGC), which automatically adjusts the amplitude from the input waveform to improve the dynamic range of the machine. The amplitude of your waveform is highly dependent on 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 manufactured by the magnetic read head is small, but will vary by a lot more than 25 dB across all swipe speeds. A set gain can be used to bring this voltage to some usable level, but to be sure the signal is at the optimum level in any way swipe speeds, AGC can be a necessity. Throughout a given swipe, a person will inadvertently change their swipe speed several times. As a result, the gain in the circuit should be adjusted through the entire swipe to make certain any changes in signal amplitude are taken into account.
There are two essential components required to implement AGC: an ADC along with a PGA. To be able to determine what gain ought to be placed on the PGA at any moment, we have to understand the current amplitude of the input waveform. The ADC could be used to monitor the input signal level and adjust the PGA when needed. 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 any magnetic card signal are really pronounced, it can be hard to have an ADC to sample the input signal with a sufficient rate so that the amplitude in the peaks in the waveform are accurately measured. To help reduce the stress in the ADC, a peak and hold circuit may be used to contain the amplitude for each peak. The 17dexbpky time where the amplitude is sampled is irrelevant, as long as the sampling and updating of your PGA occur regularly.
As a way to decode the info contained inside the waveform, the peaks in the input waveform should be detected. This can be achieved in a variety of ways, each way having benefits and drawbacks. Constructing an elementary peak detection circuit is relatively easy, but making a peak detector for magnetic stripe card reader can be challenging for many reasons:
1.The rate of your incoming peaks can vary any where from several hundred bits per second to in excess of 10 kb/s, dependant upon the swipe speed, card and card channel.
2.The amplitude of your peaks can differ greatly. This could be partially remedied with the aid of AGC, but nevertheless needs to be considered for precise peak detection.
3.The peaks from the magnetic card waveform are pronounced, however the regions between each peak can be extremely flat – which can cause noise issues in comparator or differentiator based designs.