SurvBot

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SurvBot - Remote Controller - START PART2
Ghani Lawal • 10/02/2024 at 22:06 • 0 comments
- Push buttons will connect to GPIOs
- Joysticks are 2 axis potentiometers, will connect via ADC-I2C
  - https://www.digikey.ca/en/products/filter/joystick-potentiometers/82?s=N4IgTCBcDaIFYHsCeBnALgSwMYGsQF0BfIA
  - Leaning towards "PS2 like thumb joysticks"
    - https://www.digikey.ca/en/products/detail/sparkfun-electronics/COM-09032/6823623
    - https://www.sparkfun.com/products/9032
- Screen could use I2C to keep it simple, will only be receiving data, might use SPI
- **UART used to program ESP32
- Modules:
  - Power supply
  - Motion control
  - uC & Bluetooth
  - Mode change
- CH340 USB to UART
  - will be attached to the underside of the PCB
  - USB - bottom layer
  - UART - bottom layer ->via -> top layer
- Other stuff:
  - On-of switch
  - Indicator LEDs (power, BT connected, data Tx, data Rx)
  - Emergency stop?
    - How to you implement a remote E-stop
  - Battery holder and terminals
  - Voltage levels, 3.3V for everything, maybe 5V - leaning towards the former
    - Should be able to connect to external
SurvBot - Remote Controller - START PART1
Ghani Lawal • 10/02/2024 at 21:51 • 0 comments
- Requirements:
  - Send/receive messages over Bluetooth - ESP32
  - Control robot's velocity and direction - Joystick most likely
  - Place robot in different modes and itself in different modes - push-buttons
  - Display relevant information, can choose what it displayed and how it is displayed - screen and push buttons
  - Battery powered - BT takes a lot of power
  - Programmable via USB - use a USB to UART converter
  - Simple to use IDE - Arduino
- Will take inspiration from game controllers and RC controllers
SurvBot RCU Altium Designer
Ghani Lawal • 09/18/2024 at 20:50 • 0 comments
- Finished Schematic and PCB in Altium Designer
- Made custom symbols and footprints
SurvBot PCB
Ghani Lawal • 09/04/2024 at 22:06 • 0 comments
- Finished SurvBot PCB in KiCad
- Used JLC7628 stackup
Current draw of motors
Ghani Lawal • 08/10/2024 at 21:10 • 0 comments
- Tested Motor Under no load at 6V, experimentally determined that:
  - Max speed < 180 rpm
  - Max current draw < 400mA
- Stalled Current (held motor in place while it tried to rotated at max speed)
  - < 1.5 A
  - ***May have damaged motor, no longer rotated perfectly along axis
External Memory
Ghani Lawal • 08/10/2024 at 21:03 • 0 comments
- Requirements:
  - store at least 1MB, don't need more than 10MB
  - SPI interface
  - Vdd = 3.3V
  - Recording temperature, orientation/tilt, light, current, commands
- Temperature, humidity and light: 1 sample/second
- Orientation, current, commands and speed: 10 samples/second
- Temperature and humidity from SHT30-DIS & light from ADPDS are each 2 bytes
  - 6 bytes * 1 sample/second = 6 bytes/second
  - 360 bytes/minute
  - 21600 bytes/hour
- ADC is 12-bit, will store as 2 bytes each for left motor and right motor -> 4 bytes
- Orientation sensor: roll pitch and yaw - 2 bytes each -> 6 bytes
- Commands: speed and direction - 2 bytes each -> 4 bytes
  - 14 bytes * 10 samples/s = 140 bytes/second
  - 8400 bytes/min
  - 504 000 bytes/hour
- Total: 525600 bytes/hour, stored raw this is about half a MB per hour
- Couldn't find an EEPROM
- Using NOR flash IC SST26VF032BT-104I/SM: 32Mbit
Motor Drive Unit Power
Ghani Lawal • 08/04/2024 at 16:07 • 0 comments
- Planning on powering entire device from 9V battery (unregulated supply), motor drive unit needs a 6V regulator
- Encoder operating voltage is 4.5 to 7.5V
- ***Even though STM32G0B1CE has 5V tolerant pins that are used for encoder input, the output voltage of the encoder will likely match the operating voltage
  - Will either use level shifters IC's or voltage dividers resistors, leaning towards the latter
- Since motor is rated for 6V and that is within encoder operating voltage, will use the same IC to power both
  - LM2576S-Adj, I_MAX = 3A
  - Has tips on picking out all the external circuitry and lays out a design procedure as well
Power Budget and Power Circuitry
Ghani Lawal • 08/04/2024 at 15:37 • 0 comments
- Made a "worst case scenario" power budget, this was made on July 29th,
  - Absolute max current draw by microcontroller is 100mA, but typical supply current is under 10mA, and adding peripherals only adds a 10s of uA
  - This is important because the efficiency of the buck converter under different current loads is dependent on the Inductor value, large loads -> small inductor, small loads -> large inductor
  - Therefore, want to figure out "typical" current draw before deciding on inductor values for regulators
Power From USB
Ghani Lawal • 08/04/2024 at 15:17 • 0 comments
- Can be quite noisy, use a pi filter to filter out noise
- Set up CC pins on USB_C receptacle to get 500mA from source
- ***** If inductor has no DC resistance, circuity will essentially be a resonator -> give sharp peak at corner frequency instead of trailing off
- With ESR = 0.15 ohm, the corner frequency is 1MHz, don't want to dampen below that because ICs sometime need high-frequency currents
USB Application Notes TA0357 & AN4875
Ghani Lawal • 08/04/2024 at 15:11 • 0 comments
- TA0357: Overview of USB Type C and Power Deliver Tech.
  - 2 Configuration channels (CC) for the discovery, configuration and management of USB Type C Power delivery features
  - A sink must assert Rd pull-down resistors on both CC pins
  - USB 2.0: Nominal voltage of 5V, max current of 500mA
- AN4878: Introduction to USB hardware and PCB Guidelines for STM32
  - Protection against ESD and EMI:
    - The "HBM" require that USB pins of component device be tolerant p to 2kV of discharge
    - Low Price: USBLC6-2SC6 (+ ESDA7P60-1U1M for VBUS)
    - Low Area: USBLC6-2P6 ((+ ESDA7P60-1U1M for VBUS)
  - VBUS Sensing:
    - A USB device must have VBUS sensing detection based on the USB specification
    - When the device detects the host's presence it connects its pull-up resistor to either a D+ or D- data signal line, this allows the host to detect the device presence on the bus
    - 1) If the USB device is bus powered, USB sensing isn't mandatory (USB is always connected with device is powered)
    - 2) Device is self powered - VBUS sensing is mandatory
    - ************* Not all STM32 microcontrollers that have USB peripherals have dedicated sensing pins
      If they do, it is usually - PA9 additional functions: OTG_FS_VBUS
    - ************* The embedded pull up resistor on D+ pin in STM32G0B1CE is used for USB device detection