Magnetic stripe reader having digital peak detector
View Patent ↗A point of sale terminal includes a microcontroller integrated circuit. In one aspect, a regulator within the IC receives power from a supply voltage terminal and/or a battery terminal. If the regulator does not receive adequate power from either terminal, then energy stored on-chip in a capacitor is used to erase secure memory. In another aspect, pulses of current are made to pulse through conductors of a conductive mesh. A tamper condition is detected if an improper voltage is detected on the IC terminal through which the pulse is conducted. In another aspect, each vendor signs his/her firmware with his own vendor ID. A bootloader uses the vendor ID to lookup a public key that is then used to verify a private key supplied by the firmware to be executed. In another aspect, a magnetic card reader includes a digital peak detector circuit involving programmable positive and negative thresholds.
1. A magnetic card stripe reader circuit comprising:
an analog input terminal, an analog signal having a plurality of peaks being present on the analog input terminal;
an analog front end sensor circuit that detects the analog signal on the analog input terminal and outputs a corresponding stream of digital sample values; and
a digital peak detector circuit that receives the stream of digital sample values, the digital peak detector circuit:
defines a positive minimum threshold and a negative minimum threshold;
analyzes a first portion of the stream over a first time period and above the positive minimum threshold such that a plurality of positive peaks are iteratively identified within the first portion of the stream;
analyzes a second portion of the stream over a second time period and below the negative minimum threshold such that a plurality of negative peaks are iteratively identified within the second portion of the stream;
identifies a maximum positive peak value within the plurality of positive peaks and a maximum negative peak value within the plurality of negative peaks; and
outputs a plurality of peak values including a first peak related to the maximum positive peak and a second peak related to the maximum negative peak, each peak value, within the plurality of peak values, being indicative of a corresponding one of the peaks in the analog signal, wherein the digital peak detector circuit is not part of a general purpose processor.
2. The magnetic card stripe reader circuit of claim 1 , wherein each plurality of peak values includes a number indicative of an amount of time.
3. The magnetic card stripe reader circuit of claim 1 , wherein the analog input terminal, the analog front end sensor circuit, and the digital peak detector circuit are all parts of an integrated circuit, the integrated circuit being disposed in a point of sale terminal.
4. The magnetic card stripe reader circuit of claim 3 , wherein the digital peak detector circuit analyzes a set of sample values and identifies a largest sample value in the set as being a peak value.
5. The magnetic card stripe reader circuit of claim 4 , wherein a first sample value of the set is the first sample value received into the digital peak detector after an amplitude of a sample value of the stream exceeds a first threshold value, and wherein a last sample value of the set is the last sample received into the digital peak detector after an amplitude of a sample value of the stream falls below a second threshold value.
6. The magnetic card stripe reader circuit of claim 5 , wherein the first threshold value is greater than the second threshold value.
7. The magnetic card stripe reader circuit of claim 6 , wherein the first and second threshold values are programmable.
8. The magnetic card stripe reader circuit of claim 1 , further comprising: a first-in-first-out memory that stores the plurality of peak values output by the digital peak detector circuit.
9. A method comprising:
generating an analog signal as a result of a magnetic card being swiped through a magnetic pickup circuit, wherein the analog signal has a plurality of peaks;
digitizing the analog signal and thereby creating a stream of digital sample values;
analyzing a first portion of the stream being above a positive non-zero minimum threshold over a first time period such that a plurality of positive peaks are identified within the first portion of the stream;
analyzing a second portion of the stream being below a negative non-zero minimum threshold such that a plurality of negative peaks are identified within the second portion of the stream;
identifying a maximum positive peak within the plurality of positive peaks and a maximum negative peak within the plurality of negative peaks; and
outputting a plurality of peak values including a first peak related to the maximum positive peak and a second peak related to the maximum negative peak, wherein each peak value is indicative of a corresponding one of the peaks in the analog signal, wherein said steps of digitizing and analyzing are performed by dedicated logic circuitry and not by a general purpose processor.
10. The method of claim 9 , wherein each plurality of peak values includes a number indicative of an amount of time.
11. The method of claim 10 , wherein said analyzing involves storing the plurality of peak values into a first-in-first-out (FIFO) memory.
12. The method of claim 11 , wherein said steps of generating, digitizing and analyzing are performed by an integrated circuit in a point of sale terminal.
13. The method of claim 9 , wherein said analyzing involves analyzing a set of the sample values and identifying a largest sample value in the set as being a peak value.
14. The method of claim 13 , wherein a first sample value of the set is the first sample value in the stream after an amplitude of a sample value of the stream exceeds a first threshold value, and wherein a last sample value of the set is the last sample in the stream after an amplitude of a sample value of the stream falls below a second threshold value.
15. The method of claim 14 , wherein said steps of generating, digitizing and analyzing are performed by an integrated circuit in a point of sale terminal, the integrated circuit including a processor, wherein the first and second threshold values are programmable by the processor.
16. The method of claim 15 , wherein the plurality of peak values includes positive peak values and negative peak values.
17. The method of claim 15 further comprising:
generating an interrupt signal indicative of a condition of FIFO memory, said interrupt signal being supplied to said processor.