PHY-243 Digital Electronics Agnes Scott College

PHY-243 Digital Electronics | Agnes Scott College

Circuit Analysis | Luong 1

Triple-Axis Accelerometer Breakout - MMA7361

This sensor is the centerpiece of my project and serves as the primary input for my circuit. For each axis, there is a separate sensor that outputs a voltage proportional to the degree of tilt or acceleration it experiences and these voltages control whether or not LEDs turn on or off. In this and other circuits, this sensor serves as an analog device, as the output voltage can be a wide range and is never just “on” versus “off.” As a result, the range is converted into digital by the arduino, since the input is through the analog pin on the Arduino.

This particular sensor does not need to be analog or digital, but can be either. For an Arduino, it is less computationally intensive to utilize an analog accelerometer, which is a bonus for power consumption. A digital sensor would utilize pulse width modulation for translating how intense a tilt or acceleration is, which could be read by the Arduino with equal ease, so truly, either analog or digital sensors would have worked in this project.

Left and Right Buttons

These are momentary switches that activate the “Left” or “Right” LEDs when pressed. When pressed, the circuit draws 5v through into the digital pins. I consider this component to be inherently digital, otherwise the circuit might experience lag if the signal was read as traditionally analog. When not pressed, there is no voltage going through to the digital pins, so this component is either on or off.

This part of the circuit must be digital in order to have a quick response. It is possible to consider the analog counterpart, but then the button would be pressure-sensitive, so while it is possible, it would not be practical for my quick one-push button needs.

Center LED “Blink”

This LED is always blinking in the center of my five LED array which serves as a caution signal to cars. The LED is a standard LED that does not blink regularly, and so uses a code to tell it to either be on or off. “Blink” is an inherently digital component. When the necessary voltage drop is achieved, the LED turns on as full brightness and otherwise, the LED is off.

An analog-driven LED would cause a strange dimming effect and the unused current would have to be dumped to ground, causing heat. For my application, which is a full-on / full-off blink, I cannot have dimming so this component cannot be analog.

Brake & Turn Signal LEDs

These circuits are similar. The Brake LEDs are always on if they are active, while the Turn Signal LEDs blink if they are activated. The Brake LEDs activate if the corresponding Accelerometer axis (y) experiences any “negative” acceleration, while the Turn Signal LEDs turn on if their corresponding button is pressed. Altogether, these LEDs are also digital components, since they are either full-on or off, though the Brake LEDs do occasionally flicker due to the input fluctuations.

Just as with the Center LED, an analog-driven LED would not be ideal nor would it accomplish the desired full-on/off behavior. Even if I wanted to dim my LEDs, it would be more advantageous to use PWM.