Sensing (Part Two)

From the Technology Enhancement Programme (TEP), these circuits allow students to build a range of devices. Each circuit has a full circuit diagram, component list and explanation of how the circuit works. In this section, the circuits cover a range of devices that use sensors.

Ice warning (operational amplifier)
When temperature level falls below zero degrees centigrade, a red LED will light to warn of icy conditions. If the temperature is above freezing a green LED will light.

Plant protection (heat)
This circuit is designed to protect plants in a green house. When excess heat is detected, curtains are drawn to reduce the amount of sunlight entering the greenhouse.

LM 335Z (precision temperature sensor)
This circuit is a very accurate temperature sensor that will switch on a motor when a predetermined temperature level is reached.

Wet sensor (transistor)
When the probes detect the presence of moisture, an LED will light.

Wet sensor (Darlington)
When the probes detect the presence of moisture, an LED will light.

Dry sensor (transistor)
This circuit could be used to detect if soil is too dry.

Dry sensor (Darlington)

The moisture content in soil, for example, can be detected and an LED will light to denote dry conditions.

Rain alarm
This circuit detects the presence of rain, and a buzzer sounds.

Plant watering
On detection that soil is too dry, the circuit will switch on a pump that will spray water until correct moisture level is reached.

Four light levels 

As light levels progressively increase, 4 LEDs, green, blue, red, and amber light in sequence.

Four heat levels
As the heat level rises, four LEDS green, blue, red, and yellow switch on to denote the different heat levels.

Lights out
When the three sensors (LDRs) are placed in dark conditions, an LED will light.

Steep gradient sensor
By tilting above a critical angle, the circuit is activated, and a buzzer will sound.

InfraRed sensor
When infra red beam is broken the output circuit is activated to give a warning or register a count.

Smoke alarm (deaf person)
When a normal smoke alarm sounds it activates an add on circuit which in turn will switch on a vibration motor to arouse a deaf person.

InfraRed sensor (demonstration)
This circuit is used as a demonstration. When infra red beam is broken an LED is switched off. Alternatively, a motor could be switched on, a counter could be incremented etc.

More resources on sensors can be found here.

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