AN-1044 Single input security passcode entry
A passcode entry circuit is constructed without the use of any switches, touch displays, or keypads. In this example the input uses an earbud, which also has properties of a microphone. Almost any microphone or speaker can be used in a similar fashion. When the earbud is tapped, it generates a small output pulse which is amplified by an analog comparator in the GPAK2 IC. This also initiates a string of clock pulses inside the GPAK2. Each tap gets latched as a logic “one”, while the absence of a tap gets latched as a logic “zero”. Not only does the pattern need to be correct, but also the “beat”, or timing must match as well. In other words, this circuit detects a “secret knock”. Both the pattern and timing are user configurable. The circuit to perform this must be capable of serial input pattern and timing recognition.
- AN-1044.zip- (289 KB)
Passcode, Pattern Recognition, Timing, S2P, SR Latch, CNT, DCMP, One-Shot, Digital Comparator, ACMP, Analog Comparator