Printed circuit board

The printed circuit board, or PCB is the brain that receives all the data from the bike's sensors and sends commands to the actuators based on the sensor data. The Arduino is attached to the PCB.

Overview of Individual Components

Current Sensor

This measures AC or DC current levels and provide output based on measurement. In most applications, current sensors serve as circuit protectors and current monitors. The ACS 711, the model we currently use, is an open-loop current sensor. Open-loop current sensors are usually preferred in battery-powered circuits because of their low-operating power requirements. The current sensor takes in the output from H-Bridge 1, amplifies the signal, and sends it to the DUE. The current sensor also acts as a circuit protector, where it converts the H-Bridge 5V signal to acceptable voltage of 3.3V, preventing the possibility frying the DUE's microprocessor.

Operational Amplifier (Op-Amp)

It amplifies the difference between two voltage inputs and sends this amplified signal to the DUE. In addition to its purpose, the op-amp (in combination with an RC integrator) converts a square-wave signal from the RC to a sinusoidal wave because the motor controller only accepts sinusoidal wave forms.In the report they discuss the general purpose of the op-amp, its inputs and outputs, and the reason for choosing a specific model (MCP6401). There is no documentation regarding why the team decided to change to OP344 later on (the current op-amp installed in the PCB). After looking at the specification sheets of the two components, it seems that the OP344 is better with the common mode rejection ratio. In other words, it is better in rejecting signals that are in-phase and appear simultaneously.

Opto-Isolators 1 & 2

Isolation devices allow for multiple power domains to coexist and communicate, which means that sensitive circuits are protected from switching circuits. As one can see in figure 1, the PCB is separated into two domains (5V and 3.3V), where the components placed in that domain only deal with that certain voltage. The report does go into good detail explaining the function the opto-isolator, why they chose the IL711 (which we currently use), and how it works.

Differential Line Receiver

Translates differential voltage signals into standard logic signals. In this case, it is used to reduce the noise from the transmission by differentiating two inputs and then cancelling out any differences. Since the signals transmitted from the encoder has to travel a large amount of distance to reach the DUE, a significant amount of noise is produced. The second line receiver (the lower one in the figure 1) takes in a total of six inputs from the encoder connector. Specifically, the inputs are A, B, and C. Channels A and B reads the markings of the inner disk of the encoder (i.e. the current position of the motor) and channel C outputs one pulse per revolution to indicate number of turns. Thus, the line receiver intakes these noisy signals and outputs a cleaner signal. Furthermore, we believe that the the first line receiver (the one closer to the top in figure 1) is not currently used since none of its inputs are being used.

H-Bridge 1 & 2

These components convert a source of direct current from one voltage level to another. In other words, it transforms the battery voltage (24 V) to an acceptable voltage (5V) that many of the components take in. It also allows us to, more importantly, reverse the flow of current in the output circuit or, in other words, command the bike's motor to turn in a certain direction. It is interesting to note that the SR (Slew Rate) pin on the BTN7971B (current model we use) allows the user to attach a resistor or not, which, in effect, changes the slew rate of the power switches. The current PCB has both H-Bridges attached to a 100 Ohm resistor. This prevents any overshoots in the signals that the H-Bridges sends to the bike's motor.

Voltage Regulator

As one can guess from the name, this component stabilizes the voltage to a constant level. On the PCB, the regulator takes in the voltage outputted by the DC converter and outputs the stabilized voltage to other components. The present regulator (NCV8705) is a low drop-out (LDO) linear voltage regulator. As a linear regulator, the component acts as a variable resistor, meaning the regulator adjusts the amount of resistance to vary the output voltage as desired. Furthermore, in order for a regulator to work, the input voltage must always be greater than the output voltage (in most cases the input has to be greater than the output by a minimum of 2V). LDO regulators basically reduces the minimum the input voltage has to be relative to the output voltage. The main advantages for having a LDO linear voltage regulator is because of its simplicity and they are small in size.