PH4705 & ET4305: Digital Sensors Simple switches to data words • Switch: micro-switch, reed relay, Hall sensor, optical switch….. • Threshold or Set point detector • Counting, timing, finding the frequency • Sensors that generate data words directly • Complex IC sensors that generate serial data or connect to a bus system
PH4705 & ET4305: Digital Sensors Switch Input ON/OFF information mechanical movement micro-switch, reed relay operated by a magnet Hall effect sensor
PH4705 & ET4305: Digital Sensors Switch Light Beams LDR-light dependant resistor Photo-diode Photo-transistor Slotted and reflective sensors
PH4705 & ET4305: Digital Sensors Logic Signal input ON/OFF input Compatible logic signal (voltage levels, available current)? Interference and noise?
PH4705 & ET4305: Digital Sensors Threshold or Set Point Detection Analogue input signal, detect when its value passes through a set point or threshold (in either direction)
PH4705 & ET4305: Digital Sensors Input Zero crossing detector Output Potential Divider Sets Threshold Threshold or Set Point detector Threshold detector with hysteresis
PH4705 & ET4305: Digital Sensors Counting, timing, finding frequency The required data derived from switch sensors may be: number of pulses time between pulses width of pulse frequency of pulses ………..
PH4705 & ET4305: Digital Sensors Data Words Typical example is this optical coded disc used to detect angular position. Looking along a radius gives an 8-bit word or a resolution of 1/256. (Looking at the pulse rate of, say, the outside markings will also yield speed.)
PH4705 & ET4305: Digital Sensors Complex IC digital sensor Sensors system ICs that have signal processing and generate digital data as a serial data streams or connect directly to a microprocessor system data bus. Examples: CCD digital camera sensor, SHT75 temperature/humidity module