Electronic Speed Controlled Car

According to the National Highway Traffic Administration’s fact sheet for 2005, one of the leading causes of car accidents, resulting in fatalities is speeding. “Speeding reduces a driver’s ability to steer safely around curves or objects in the roadway, extends the distance necessary to stop a vehicle, and increases the distance a vehicle travels while the deriver reacts to a dangerous situation.”

The main goal of the project is to increase safety in highway/roadways as well as urban and residential streets. Ultimately this idea will not only increase the driver’s safety, but also the safety of pedestrians.

The intention is to develop a new system that could help out in the near future. It's an "electronic speed controller" that uses sensors mounted in front of the car that scans the road ahead for “electronic speed signs,” which are normal visual speed signs that have radio frequency transmitters mounted to them that transmit a specific speed limit frequency. Once a car has entered the speed limited zone, and has received the signal from the “electronic speed signs,” the car’s speed is restricted to that, and the car will not be able to exceed the speed limit. The car will also be able to see the see the speed on the dashboard that will inform the driver of the current speed limit posted to that specific zone.

This article is to demonstrate how this system is going to work by using a remote controlled car. The remote controlled car will have a transceiver that will serve for two purposes. First it will receive the signals coming from the electronic speed signs, and secondly, it will transmit the speed limit information to an LCD mounted on the remote control so the user can see it. Once the car receives the signal from the electronic speed sign, that signal will then go through a microcontroller that will regulate the amount of power being supplied to the car’s electric motor by adjusting the pulse width modulation.

How the RC Car works
Electronic Speed Sign

The electronic speed sign consist of a circuit board which features a microcontroller, a power supply (portable 9V battery), a built in 5V voltage regulator and a RF transmitting antenna. The microcontroller is programmed (by the user) to transmit a radio frequency (x value) which contains information that will tell the radio controlled car not to go over a certain speed limit.

For the electronic speed sign, integrates the 433 MHz RF Transmitter into the concept. This transmitter will transmit radio frequencies at 433MHz UHF to the RC car’s transceiver. The integration of a Super Carrier Board - serial version with an input of 9V provided by a battery. This system features a 5V voltage regulator that will step down the voltage from 9V down to 5V. This will prevent the microcontroller and the RF transmitter from being damaged. The development board has a serial connector integrated to the PC board that will allow to easily program the microcontroller and/or make changes to the setup of the electronic speed sign in the future if may choose to do so. This kit is complemented by a Basic Stamp 2 microcontroller that should be programmed (by the user) to transmit frequencies of 433MHz UHF to the car. This microcontroller operates at 20MHz and can execute approximately 4,000 instructions per second, and is more than enough for this purpose. The voltage regulator, LM2940/LM2940C 5V regulator, it is a simple transistor like component that has 3 leads input, output and ground and will be used to drop the high 9V supplied by the battery down to a low of 5V which is the ideal voltage to operate the electronic speed sign’s circuitry.

RC Car

The RC car receives the information being transmitted from the electronic speed sign (E.S.S). The transceiver package is used to receive information and later to transmit. The information which contains the speed limit restriction posted is repeated to the remote controller which will be in possession of the user. The other part of the signal that was received by the remote controlled will be analyzed in the car’s internal circuitry, which will be custom rebuilt. The information will be processed through a microcontroller for analysis, which will then tell the pulse width modulator that controls the car’s h-bridge how fast the car should be going forward. The h-bridge is a circuit in the car that controls the forward and reverse movements of the car’s DC motor.

All transmitters and receivers should be from one source which ensures compatibility between the systems when transmitting and receiving RF data. RF modules operate at a compatible frequency of 433MHz UHF. A Development Board - Serial Version will be used to hold the internal circuitry of the car. Again this board features a serial port that will allow the programmer to access the microcontroller for settings change and easy troubleshoot without having to disassemble the circuit. Like the electronic speed sign a 9V to 5V regulator will be used to step down the voltage to the circuit.

Next step is the microcontroller for this system. Basic Stamp 2, this is just like the one used in the electronic speed sign. It’s a 20MHz processor that can execute approximately 4,000 instructions per second. The MCU will be used to receive the signal from the transmitter in the electronic speed sign and do a compare function by using IF THEN STATEMENT to call the appropriate subroutine. After the appropriate subroutine is called, it will then transmit the signal to the electronic speed display. The sub-routine will also include a code which will adjust the PWM thus regulating the speed of the DC motor.

A pulse width modulator needs to be included. This device can have up to 4 PWM outputs that can be independently controlled by the MCU, in case need to run the front steering motor to control the direction of the car. “The PWMPAL receives a serial command from the MCU, then configures and controls the PWMPAL I/O. The motor control outputs will be a TTL level square wave. The frequency and period of this waveform is determined by a control valued sent to the PWMPAL from the host.” “The PWMPAL controls the motor on/off time values by controlling the frequency duty cycle. The on/off times are specified with 16-bit values in units of 25 microseconds, using the formula standard frequency/period. (Frequency = 1/period.)”

RC Remote Controller

For the remote controller, need a 433 MHz RF receiver. The job is to pass the information coming from the car to the MCU inside the internal circuit of the remote control. The receiver will be powered by a 9 volt battery, but the voltage will need to be step down to 5 volts, which is the operating power required by the receiver. The use of a 5 volt regulator will be required to perform this function.

The receiver will be connected to a Basic Stamp 2 through the PC board. This board will hold all of the electronic components necessary for this circuit. This processor is similar to the ones being used for the other 2 components. It’s a 20MHz processor that can execute approximately 4,000 instructions per second, and again this is more than enough to accommodate. Since the power required to operate this microcontroller can fall between 5 - 15 volts DC, it is recommended to power the chip straight from the 9volt battery. The purpose for this microcontroller is to output a message to the LCD screen.

The LCD display should a 2x16 LCD. The LCD display is two lines by 16 characters and provides basic text wrapping, it will have background lid so the end-user can see it’s screen message whether it is day or night. It supports the same visible characters as the BASIC Stamp Editor’s Debug Terminal (ASCII Dec 32-127). In addition, it can define up to eight of your own custom characters to display anywhere on the LCD screen if choosen to do so. The sole purpose of this LCD screen is to display to the end-user information coming from the microcontroller. It should be mounted on the front of the remote controller for an easy visual.

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