LDC1101: Raspberry Pi 4 via SPI – All Registers 0x00 or LHR Data Always Zero

Tool/software:

Hi all,

I'm currently working with the Texas Instruments LDC1101 connected to a Raspberry Pi 4 Model B using SPI, and I'm having trouble getting reliable communication. Specifically, I am using an LDC1101 Click (MIKROE-3240), which already has a coil attached to it.

Here's what's happening:

1. Sometimes all registers read as 0x00, including the CHIP_ID register (which should return 0xD4). I’m not sure why this happens, since I have already conducted a continuity test and a loopback test (by connecting MISO and MOSI without the sensor) and they all came back fine. Sometimes rebooting helps, sometimes not.

2. When I do get a valid CHIP_ID and the SPI seems to be working, the LHR_DATA register always returns zero, and the LHR_STATUS register stays at 0x01.

I suspect that I may be forgetting to configure one or more critical registers needed to enable LHR mode properly. Maybe I'm missing a write to set a specific bit in RCOUNT or LHR_CONFIG, but I'm not sure.

I’ve attached the Python source code I’m using to communicate with the LDC110 and a table showing the wiring/connections between the Raspberry Pi and the LDC1101 board If anyone has experience with this device and SPI communication on the Pi, I’d really appreciate any advice on what could be causing these issues.

Thank you in advance.

import spidev
import time
import RPi.GPIO as GPIO

# === SPI and GPIO Config ===
SPI_BUS = 0
SPI_DEVICE = 0
SPI_SPEED = 50000  # 50 kHz
SPI_MODE = 0b00    # Mode 0: CPOL = 0, CPHA = 0

CS_PIN = 8   # GPIO8 (CE0)
SCK_PIN = 11 # Clock
MISO_PIN = 9 # MISO
MOSI_PIN = 10 # MOSI

# === LDC1101 Register Addresses ===
REG = {
    "START_CONFIG": 0x0B,
    "RP_SET": 0x01,
    "TC1": 0x02,
    "TC2": 0x03,
    "DIG_CONFIG": 0x04,
    "ALT_CONFIG": 0x05,
    "RP_THRESH_H_MSB": 0x07,
    "RP_THRESH_L_LSB": 0x08,
    "RP_THRESH_L_MSB": 0x09,
    "INTB_MODE": 0x0A,
    "D_CONF": 0x0C,
    "L_THRESH_HI_LSB": 0x16,
    "L_THRESH_HI_MSB": 0x17,
    "L_THRESH_LO_LSB": 0x18,
    "L_THRESH_LO_MSB": 0x19,
    "STATUS": 0x20,
    "RP_DATA_LSB": 0x21,
    "RP_DATA_MSB": 0x22,
    "L_DATA_LSB": 0x23,
    "L_DATA_MSB": 0x24,
    "LHR_RCOUNT_LSB": 0x30,
    "LHR_RCOUNT_MSB": 0x31,
    "LHR_OFFSET_LSB": 0x32,
    "LHR_OFFSET_MSB": 0x33,
    "LHR_CONFIG": 0x34,
    "LHR_DATA_LSB": 0x38,
    "LHR_DATA_MID": 0x39,
    "LHR_DATA_MSB": 0x3A,
    "LHR_STATUS": 0x3B,
    "CHIP_ID": 0x3F,
}

# === Device Constants ===
DEVICE_OK = 0x00
DEVICE_ERROR = 0x01

# Power Modes
ACTIVE_MODE = 0x00
SLEEP_MODE = 0x01
SHUTDOWN_MODE = 0x02

# === SPI Init ===
spi = spidev.SpiDev()
spi.open(SPI_BUS, SPI_DEVICE)
spi.max_speed_hz = SPI_SPEED
spi.mode = SPI_MODE

# === GPIO Init ===
GPIO.setmode(GPIO.BCM)
GPIO.setup(CS_PIN, GPIO.OUT)
GPIO.setup(SCK_PIN, GPIO.OUT)
GPIO.setup(MISO_PIN, GPIO.IN)
GPIO.setup(MOSI_PIN, GPIO.OUT)

# === Helper Functions ===

def write_register(addr, value):
    GPIO.output(CS_PIN, GPIO.LOW)
    spi.xfer2([addr & 0x7F, value])
    GPIO.output(CS_PIN, GPIO.HIGH)

def read_register(addr):
    GPIO.output(CS_PIN, GPIO.LOW)
    resp = spi.xfer2([addr | 0x80, 0x00])
    GPIO.output(CS_PIN, GPIO.HIGH)
    return resp[1]

# === Initialization ===

def initialize_ldc1101():
    chip_id = read_register(REG["CHIP_ID"])
    if chip_id != 0xD4:
        print(f"Unexpected CHIP ID: 0x{chip_id:02X}")
        return DEVICE_ERROR

    write_register(REG["RP_SET"], 0x07)
    write_register(REG["TC1"], 0x90)
    write_register(REG["TC2"], 0xA0)
    write_register(REG["DIG_CONFIG"], 0x03)
    write_register(REG["ALT_CONFIG"], 0x00)
    write_register(REG["RP_THRESH_H_MSB"], 0x00)
    write_register(REG["RP_THRESH_L_LSB"], 0x00)
    write_register(REG["RP_THRESH_L_MSB"], 0x00)
    write_register(REG["INTB_MODE"], 0x00)
    write_register(REG["START_CONFIG"], SLEEP_MODE)
    write_register(REG["D_CONF"], 0x00)
    write_register(REG["L_THRESH_HI_LSB"], 0x00)
    write_register(REG["L_THRESH_HI_MSB"], 0x00)
    write_register(REG["L_THRESH_LO_LSB"], 0x00)
    write_register(REG["L_THRESH_LO_MSB"], 0x00)
    write_register(REG["LHR_RCOUNT_LSB"], 0x00)
    write_register(REG["LHR_RCOUNT_MSB"], 0x00)
    write_register(REG["LHR_OFFSET_LSB"], 0x00)
    write_register(REG["LHR_OFFSET_MSB"], 0x00)
    write_register(REG["LHR_CONFIG"], 0x00)
    time.sleep(0.1)

    return DEVICE_OK

# === Mode Config ===

def set_powermode(mode):
    write_register(REG["START_CONFIG"], mode)

def enable_lhr_mode():
    write_register(REG["LHR_RCOUNT_LSB"], 0x00)
    write_register(REG["LHR_RCOUNT_MSB"], 0x80)
    write_register(REG["LHR_OFFSET_LSB"], 0x00)
    write_register(REG["LHR_OFFSET_MSB"], 0x00)
    write_register(REG["LHR_CONFIG"], 0x01)

# === Data Fetch ===

def read_lhr_data():
    msb = read_register(REG["LHR_DATA_MSB"])
    mid = read_register(REG["LHR_DATA_MID"])
    lsb = read_register(REG["LHR_DATA_LSB"])
    return (msb << 16) | (mid << 8) | lsb

# === Debug ===

def display_all_registers():
    print("=== LDC1101 Register Dump ===")
    for name, addr in REG.items():
        try:
            val = read_register(addr)
            print(f"{name:20s} (0x{addr:02X}): 0x{val:02X}")
        except Exception as e:
            print(f"{name:20s} (0x{addr:02X}): Error: {e}")

# === Main ===

def main():
    if initialize_ldc1101() != DEVICE_OK:
        print("Initialization failed.")
        return

    print("LDC1101 initialized successfully. Switching to LHR mode...")
    set_powermode(ACTIVE_MODE)
    enable_lhr_mode()
    time.sleep(1)

    try:
        while True:
            lhr = read_lhr_data()
            print(f"LHR Data: {lhr}")
            time.sleep(0.5)
    except KeyboardInterrupt:
        print("\nTerminated by user.")
    finally:
        spi.close()
        GPIO.cleanup()

if __name__ == '__main__':
    main()