ph4705 & et4305: digital sensors simple switches to data words –switch: micro-switch, reed...
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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
Threshold detector with hysteresis
Zero crossing detectorInput
Output
Potential Divider Sets Threshold
Threshold or Set Point detector
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 WordsTypical 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