DE - Signal Amplification:

Why is important for the output voltages of small signals produced by sensors need to be amplified?

• It is important to amplify them before putting them into the ADC, so that they produce a good range of output values.

Give examples of sensors (input devices) that use an amplifier?

• Microphones produce very small signals and will require a pre-amplifier.

• A load cell will need connecting to an instrumentation amplifier to produce an analogue signal large enough to be registered by the ADC.

What is the problem with microcontroller output pins? How can this be resolved?

• They only supply small amounts of current (in mA) which is only sufficient enough to light a small LED or sound a button.

• Hence, for most output devices, a driver is used to amplify the output current to a level where the device works properly.

What is a common type of driver used to amplify the output current? Explain its features:

• A MOFSET

• Has 3 leads: gate(g), drain(d) & source(s).

Sketch how a MOFSET is connected to a circuit that is powering an electric motor or solenoid is used:

• Circuit that connects to a voltage, MOFSET, motor/solenoid & diode across the component.

• Note: If LEDs or buzzers are being used, the diode can be omitted.

Why is a diode needed for a MOFSET driving an electric motor or a solenoid?

• As a protection device for the MOSFET.

• Electric motors & solenoids generate high voltage electrical ‘spikes’ (called ‘back EMF’) which can damage the MOSFET.