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A voltage regulator takes a higher voltage and provides a set voltage that the regulator is designed to output. There are a few types of regulators: switching regulators, high dropout regulators and low dropout regulators. Regulators have an input and an output. The input is the raw voltage that you provide through battery, wall adapter, power supply, transformer (with rectification and smoothing with capacitors). The output is the voltage that the regulator is designed to provide.

Dropout is the amount of voltage the regulator needs to keep the rated output voltage.

Examples of common voltage regulators:
7805 - provides 5 volts and is a high dropout
Max603 - 5v output
Max604 - 3.3v output

The 7805 Voltage regulator outputs 5 volts and requires at least 8 volts at the input (high dropout voltage). The middle pin is connected to ground.

Capacitors are needed to reduce the peak to peak (pk-pk) voltage difference which is considered noise from the power supply. The capacitors can also reduce interference from outside sources and from devices in the circuit.

A 10uF (microFarad) capacitor is used at the input side.
A .1uf capacitor is used at the output side.

The 7805 voltage regulator is connected to a breadboard to provide 5 volts to the circuit. Two capacitors are connected to the voltage regulator, 10uf (microfarad) on the input and .1uf on the output to reduce the peak to peak voltage difference.

Two sets of batteries are tested with this voltage regulator and the voltage dropout is determined by subtracting the input voltage to the output voltage.

The minimum recommended input voltage is 8 volts and the determined dropout is 1.5 volts. The 8 volts gives a .5 volt margin.

The MAX603 is a Voltage Regulator that will provide 5v output and can accept a voltage very close to this output voltage featuring its low dropout.

The input voltage is connected to pin 1 and the output of 5v is from pin 8. the two middle pins on each side is connected to ground. Pin 4 is the off pin and to have the regulator enabled, this pin must be connected to the input voltage or pin.

The set pin at pin 5 is a pin that if it is connected to gnd, that pin will tell the chip to use the set voltage output of 5v. If a resistor is connected to this pin, the output voltage can be modified.

A capacitor is connected between the output pin and gnd and another capacitor is connected to input and gnd. Both capacitor values are 10uF (microfarad)

A wall adapter can be used to power the microcontroller circuit. It is recommended to use a voltage regulator with this wall adapter to insure that the proper voltage is powering the circuit. Too much peak to peak deflection in the power can cause unpredictable results and even damage the components.

The USB from the computer can be used to power the microcontroller circuit. The USB power is already a regulated power source, but another regulator can be connected with this input power. It is also recommended to use a 10uf (microfarad) capacitor at this input point (between the gnd and input voltage)

The AC (Alternating Current) first goes through a transformer to step down the voltage from the mains power (110v or 220v). The sine wave after the transformer is now a much more narrow sine wave, only peaking at the voltages corresponding to the transformer.

Rectification - using 4 diodes, or a bridge rectifier (which is 4 rectifier diodes) the sine wave portion that is in the negative region can be flipped up (or folding up) to the positive region. At this point, the AC looks more like hills rather than a sine wave. This happens because the diodes only let the current flow in one direction. The diodes are positioned and oriented in a way that makes both negative and positive portions of the sine way happen only in the positive direction.

The waveform (bumps) now need to be smoothed to match more like a line (DC). Adding capacitors will charge up like a battery and release the energy slowly. This creates a smoothing effect for the bumpy waveform.

To get the current to a specific voltage level to be used in the circuit, a voltage regulator is used. If a high dropout voltage regulator is used, the voltage level before the voltage regulator must be higher than the regulated voltage plus the dropout amount.

Regulators are used after the power supply has been converted to DC from AC. The regulator requires capacitors to create a current that the regulator will accept. The lowest portion of voltage on the input waveform must be the consideration for the lowest voltage acceptable to the voltage regulator to get the output voltage needed for the circuit.

The 7805 voltage regulator requires a .1 uf (microfarad) capacitor helps transient response.

Since this Freescale accelerometer requires a different voltage than the AVR microcontroller, another voltage regulator is used (Maxim MAX604). The MAX604 will be positioned on the other extreme side of the breadboard. The MAX604 uses 2 10uf capacitors to smooth the power signal at the input and the output. One portion of the power rails is dedicated to the 3.3v so the accelerometer can easily be connected to power.

To convert more than one analog signal using the ADC, multiple channels must be used. In this case, an accelerometer will be connected to channel 0 and channel 1 of the ADC. The X axis is connected to channel 0 and the Y axis is connected to channel 1.

To smooth the analog signals, 10 uf (micro farad) capacitors will be used on each channel.

To power the accelerometer, the MAX604 voltage regulator with supporting capacitors are used.

The pressure sensor is connected to the MAX604's output voltage to pin 2 of the sensor for VCC and pin 3 for GND.