Analogue sensors

All analogue boards are based on the same principle and actually use the same PCB. The only difference is the sensor itself, which is placed between the pins marked “S” and “G”.

The two 100k resistors (R3 and R5) provide a voltage divider which creates a voltage corresponding to Vcc/2. This Voltage is compared to the voltage of a second voltage divider consisting of the sensor (installed between S= signal, and G=ground) followed by the 150 Ω resistor R4 and the potentiometer. The two voltages are compared by the LM393 voltage comparator between pins 2 and 3. The voltage level of the second divider is taken out on the A0 pin of the PCB connector, while the output of the comparator is connected to D0. D0 therefore shows which of the 2 voltages is higher. This is also indicated by LED2 (green LED) which lights when the output of the second comparator goes low. This is is case when the D0 output goes high.

LED1 simply lights when the board is powered.

These are the analogue boards available in the kit:

• big and small microphone

• flame sensor

• hall sensor

• thermistor

flame sensor	hall sensor	thermistor

• touch sensor and a
• reed switch

touch sensor	reed switch

Uli Raich - 2017-01-08

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