Sensing (Part One)

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.

Poor light indicator
When light begins to fade, an LED flashes. The level of light at which the LED begins to flash can be set by use of a variable resistor.

Curtain controller
When sunlight becomes too bright the circuit will switch on a motor that will draw the curtains. In the absence of sunlight, curtains are reopened.

Dark sensor (transistor)
When light level falls below a certain value. An LED will light. The light level at which the LED will light can be set by use of a variable resistor.

Dark sensor (Darlington)
When light level falls below a certain level, an LED lights. The light level at which the LED will light can be set by use of a variable resistor.

Light sensor (transistor)
At a predetermined light level an LED will light.

Light sensor (Darlington)
At a particular light level a buzzer sounds.

Dark sensor (no adjustment)
In dark conditions an LED lights. In bright conditions the LED is unlit.

Light intensity
This circuit is designed to give an audible warning as light level increases. As light gets brighter the rate at which the buzzer sounds will increase.

Light sensing (operational amplifier)
When light increases to a certain level, a motor switches on.

Remote sensing (fibre optic cable)
This circuit is remotely controlled using a fibre optic link. When light shines on the sensor, a motor will turn or alternatively a solenoid is activated.

Cold sensor (transistor)
When temperature falls below a certain level, an LED will light.

Cold sensor (Darlington)
When the temperature falls below a certain level, an LED lights. The temperature at which the LED will light can be set by use of a variable resistor.

Heat sensor (transistor)
As temperature increases, an LED lights at a certain level, which can be set by adjustment of variable resistor.

Heat sensor (Darlington)
As temperature increases, at a certain degree of heat the LED will light.

Heat sensor (operational amplifier)
When the temperature increases to a certain level, a motor switches on.

More resources on sensors can be found here.

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