[LCSC Development Board] Smart Car (LCSC 2023 Winter Camp)

The target
design is an intelligent car based on the Liangshanpai development board.

Functions include: basic movement (forward, backward, and steering), infrared tracking, ultrasonic obstacle avoidance, Bluetooth remote control, battery detection, and low battery warning.
Technical Stack:
Hardware fundamentals (circuit design, PCB, soldering),
programming skills (C, software fundamentals and software debugging),
information retrieval,
problem-solving skills,



schematic design instructions
, pin assignment



, connection labels,
pin
descriptions.




Motor




LF+
PB4
Left front wheel +


LF-
PA7
Left front wheel -


RF+
PA3
Right front wheel +


RF-
PA2
Right front wheel -


LB+
PB0 Left
rear wheel +


LB-
PB1 Left rear wheel
-


RB+
PA0 Right rear
wheel +


RB-
PA1 Right rear wheel - Tracking XJ01 PA15 Tracking 01 XJ02 PC10 Tracking 02 XJ03 PC12 Tracking 03 XJ04 PB13 Tracking 04 XJ05 PB15 Tracking 05 Button KEY_M PB5 Sport mode switch button KEY_S PE5 Start sport button LED LED_L PA12 Left headlight LED_R PG7 Right headlight LED_M PB3 KEY_M Indicator LED_S PE2 KEY_S Indicator Bluetooth STATE PF9 Status pin TXD PF7 microcontroller's serial transmit pin RXD; PF6 microcontroller's serial receive pin EN; PF10 enable pin; PB12 ultrasonic module TRIG pin; PB10 ultrasonic module TRIG pin ECHO pin; PB10 ultrasonic module ECHO pin; Buzzer BUZZER; PF8 buzzer ; ADC ; PC5 ADC voltage detection power supply. Power requirements analysis: Liangshanpai development board: 3.3V or compatible 5V (3.3V output available) ; Tracking circuit: 5V; Ultrasonic module: 5V; Buzzer: 5V; Bluetooth module: 3.3V; Motor driver: RZ7899 chip, not exceeding 25V. Power supply design: Uses 14500 lithium batteries (two in series, 7.4V). Then, through a Schottky diode and a toggle switch, it is connected to a linear regulator (LDO), which outputs a stable 5V DC voltage. The motor driver is powered directly from the lithium battery VCC, approximately 7.4V. Bluetooth power comes from the Liangshanpai development board, 3V. Other components are powered from the LDO, 5V. Component Functions and Connections: Schottky Diode: Prevents reverse battery connection; SS34 is selected. Positive terminal connects to the lithium battery, negative terminal connects to the toggle switch. Toggle Switch: Controls power supply on/off. LDO: Reduces battery voltage to a stable 5V to power other components in the circuit that require 5V input. Input connects to VCC, output connects to two capacitors for filtering to prevent interference. LED: Indicates power supply on/off. Positive terminal connects to VCC, negative terminal connects to GND through a current-limiting resistor. In this example, the LEDs include two parts: status indicator and lighting. Status display LEDs will be described in the corresponding modules; here we only focus on the lighting LEDs. Lighting: LED_L and LED_R for vehicle lighting. Component Connections: Status display LEDs will be described in the corresponding modules; here we only focus on the lighting LEDs. Buttons : Primarily used for status switching. Component Functions and Connections: KEY_M: Mode button. One end connects to the GPIO input pin, the other end is grounded. KEY_S: Start button. One end connects to the GPIO input pin, the other end is grounded. [Note]: When the button is pressed, the GPIO port is at a low level. Therefore, the GPIO needs to be configured as a pull-up input mode to detect the low level. Alternatively, a pull-up resistor can be added to pull the IO level high, thus eliminating the need for pull-up input configuration. For motor driving , since the microcontroller's IO current is very weak and cannot drive the motor rotation properly, a motor driver chip must be used. The RZ7899 motor driver chip is selected here.















































































































































































The RZ7899 is a DC bidirectional motor drive circuit suitable for automatic valve motor drives, electromagnetic door lock drives, etc. This circuit features good anti-interference capabilities, minimal standby current, and low output resistance. It also has a built-in diode to release reverse inrush current from inductive loads.
Two logic input terminals, BI and FI, control the motor's forward, reverse, and braking. By connecting BI and FI to the microcontroller's I/O ports and changing the microcontroller's I/O port level, the output pin level of the chip's control terminal can be changed, allowing for forward/reverse rotation, stopping, and braking control of the motor. Connecting the BI and FI pins to the microcontroller's timer channel pins allows for the use of the microcontroller's timer PWM output function to control the motor speed, thereby changing the speed of the intelligent vehicle.
Features of the RZ7899 chip:

minimal standby current (less than 2uA); wide operating voltage range (3.0V~25V);
emergency stop function; overheat protection;
overcurrent and short-circuit protection; SOP8 package.


Truth table for the driver chip:
Component connection instructions:

BI: Back input. Connect to the timer channel pin of the microcontroller.
FI: Forward input. Connect to the timer channel pin of the microcontroller.
BO: Back output. Connect to the motor pin.
FI: Forward output. Connect to the motor pin.
GND: Ground.
VCC: 7.4V. Before using the

ADC voltage acquisition circuit
, it is necessary to know the ADC's bit depth (i.e., accuracy). According to the user manual, the GD32's ADC is 12-bit, so the accuracy is 2^(12) - 1 = 4095, and the accuracy range is 0~4095. Since the I
/
O port is only compatible with a maximum of 5V, exceeding 5V will burn out the I/O port. The battery's operating voltage is 7.4V (maximum 8.4V, minimum 6.6V), which exceeds the I/O port's maximum compatible voltage. Therefore, a voltage divider circuit is needed. The voltage after voltage division should not exceed the I/O port's maximum compatible voltage.
So, how do we calculate the actual value of the acquired voltage from the ADC value?

Linear mapping. Calculation process: Premise: Assume the ADC is 12-bit, the battery power supply is a maximum of 8.4V and a minimum of 6.6V (below which an alarm will be triggered to remind charging);
-------Calculate the ADC value knowing the voltage-------
(1) The voltage ratio of the ADC terminal: 10K/(10K+10K+10k)≈0.3333;
(2) When the battery power is at its highest, the voltage obtained by the voltage divider at the ADC terminal is: 0.3333*8.4V≈2.7997V
When the battery power is at its lowest, the voltage obtained by the voltage divider at the ADC terminal is: 0.3333*6.6V≈2.1998V
If we refer to 3V, that is, 3V when fully charged and 0V when
depleted, the ADC value when the battery power is at its highest is: (2.7997/3V)*4095=3821
The ADC value when the battery power is at its lowest is: (2.1998/3V)*4095=3002
-------Calculating Voltage from ADC Value-------
If we refer to 3V, that is, 3V when fully charged and 0V when de-charged;
through the inverse operation of the above formula, we know that the voltage value corresponding to any ADC value is: V_value=(ADC*3)/4095 Unit: V


Buzzer
The buzzer uses an active buzzer with a built-in oscillation source, which will sound as long as it is powered on. However, because the pin driving capability of the microcontroller is weak, it cannot directly drive the buzzer. Therefore, a PNP transistor is used as an electronic control switch, and the buzzer's on/off state is controlled by the output voltage of the microcontroller's I/O.

When the I/O output is high, the voltage at the emitter is not much greater than the base voltage, the transistor is not conducting, and it is in the cutoff state, so the buzzer does not sound. When the
I/O output is low, the voltage at the emitter is much greater than the base voltage, the transistor conducts, current flows from the emitter to the collector, and the buzzer sounds.

Component Function and Connection Instructions:

Buzzer: The positive terminal is connected to the collector of the transistor, and the negative terminal is connected to GND.
1k resistor: Current-limiting resistor to prevent excessive current from entering the GPIO.
10k resistor: Interference protection resistor. Connected between the emitter and base.
PNP transistor: Emitter connected to +5V, base connected to the GPIO pin via the current-limiting resistor, collector connected to the positive terminal of the buzzer. For

Bluetooth
, directly select a Bluetooth module. When selecting, pay attention to the VCC value (5V OR 3.3V) and ensure proper power supply matching.
Also, when connecting the microcontroller pins, pay attention to the serial port pin connections: Bluetooth RXD --- Microcontroller TXD, Bluetooth TXD --- Microcontroller RXD.
Use a 1*6 2.45mm header to draw the schematic. For
ultrasonic testing
, select an HC-SR04 ultrasonic module.
Ensure the receive and transmit pin connections are correct. Use a 1*4 2.45mm header to draw the schematic.
The tracking
circuit design utilizes the principle that infrared light reflects differently when encountering different colored ground surfaces. The tracking circuit uses the ITR9909 infrared photoelectric switch, which integrates an infrared emitter and receiver. A five-channel tracking circuit is used, with sensitivity adjustable for each channel via a variable resistor. An LM393 voltage comparator chip is used; since one comparator chip supports two channels, only three comparator chips are needed.

The principle for detecting black lines is that the infrared emitter emits light to the ground; when the infrared light encounters a white surface, it is reflected, and the infrared receiver receives the reflected light. After passing through the voltage comparator, the output is low.
The principle for detecting black lines is that the infrared emitter emits light to the ground; when the infrared light encounters a black surface, it is absorbed, and the infrared receiver does not receive the reflected light. After passing through the voltage comparator, the output is high.

The comparator's output pin is connected to the microcontroller's GPIO, and the GPIO is set to input mode.
The schematic
diagram is organized, separating different modules with boxes and providing explanations.
The PCB layout and wiring are shown in
the Bluetooth APP
demonstration.