FAQ & Troubleshooting

Frequently asked questions and solutions for common problems when working with DimmerLink.

Connection Problems

No Response from Device

Symptoms: I send a command, but there's no response.

Possible causes and solutions:

I2C Diagnostics:

# Linux/Raspberry Pi
i2cdetect -y 1

If the device is working, address 50 will appear in the table.

UART Diagnostics:

import serial
ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=1)
ser.write(bytes([0x02, 0x52]))  # Request frequency
print(ser.read(2).hex())  # Expect "0032" or "003c"

I2C Doesn't See Device

Symptoms: i2cdetect shows empty table, address 0x50 not displayed.

Solutions:

1. Check pull-up resistors
2. Raspberry Pi: built-in 1.8kΩ usually sufficient
3. Other boards: add external 4.7kΩ
4. Check wiring
   SDA → SDA (not crossed!) SCL → SCL
5. Check wire length
6. I2C: maximum 30 cm without buffers
7. For longer distances use UART
8. Check if I2C is enabled
   bash # Raspberry Pi sudo raspi-config # Interface Options → I2C → Enable
9. Check bus number
   bash ls /dev/i2c-* # May be i2c-0 or i2c-1 i2cdetect -y 0 # try different bus

Permission Denied (Linux)

Symptoms: PermissionError: [Errno 13] Permission denied: '/dev/ttyUSB0'

Solution:

# Add user to groups
sudo usermod -a -G dialout,i2c $USER

# Log out and back in, or reboot
logout

Device Not Responding After Interface Switch

Symptoms: After SWITCH_I2C command (0x5B) or SWITCH_UART (via I2C), device doesn't respond.

Cause: This is normal behavior. After switching interfaces, the old interface is disabled.

Solutions:

1. After UART → I2C:
2. Connect to device via I2C
3. Default address: 0x50 (or previously configured)
4. Check: i2cdetect -y 1
5. After I2C → UART:
6. Connect to device via UART
7. Speed: 115200, 8N1
8. If you changed the I2C address:
9. Scan the bus: i2cdetect -y 1
10. Device will be at the new address

Example switching UART → I2C:

import serial
from smbus2 import SMBus

# 1. Send switch command via UART
ser = serial.Serial('COM3', 115200, timeout=1)
ser.write(bytes([0x02, 0x5B]))  # SWITCH_I2C
resp = ser.read(1)
if resp and resp[0] == 0x00:
    print("Switched to I2C")
ser.close()

# 2. Now work via I2C
bus = SMBus(1)
freq = bus.read_byte_data(0x50, 0x20)
print(f"Mains frequency: {freq} Hz")

Protocol Errors

Error 0xFC — EEPROM Write Error

Cause: Failed to save settings to non-volatile memory.

Possible causes:
- Flash memory problem
- Power supply voltage too low

Solution:
- Check power supply voltage (minimum 2.7V for Flash write)
- Retry the command

Error 0xF9 — Syntax Error

Cause: Unknown command or invalid format.

Check:

1. Start byte — command must begin with 0x02
2. Command code — use only valid codes:
3. 0x53 (SET)
4. 0x47 (GET)
5. 0x43 (CURVE)
6. 0x51 (GETCURVE)
7. 0x52 (FREQ)
8. 0x58 (RESET)
9. 0x5B (SWITCH_I2C)

Example of correct command:

Correct:   02 53 00 32  (SET brightness 50%)
Incorrect: 53 00 32     (no start byte)
Incorrect: 02 99 00     (unknown command 0x99)

Error 0xFD — Invalid Index

Cause: Non-existent dimmer index specified.

Solution: Use index 0x00. Current version supports only one dimmer.

Correct:   02 53 00 32  (dimmer 0)
Incorrect: 02 53 05 32  (dimmer 5 doesn't exist)

Error 0xFE — Invalid Parameter

Cause: Parameter value outside allowed range.

Check:
- Brightness: 0-100 (not 0-255!)
- Curve: 0, 1, or 2
- I2C address: 0x08-0x77

Correct:   02 53 00 64  (brightness 100%)
Incorrect: 02 53 00 FF  (255 > 100)

Correct:   02 43 00 02  (LOG curve)
Incorrect: 02 43 00 05  (curve 5 doesn't exist)

Dimming Issues

Lamp Doesn't Light at Low Brightness

Symptoms: Incandescent lamp doesn't light below 25% brightness.

Cause: This is normal behavior for incandescent lamps. At low power levels, filament heating is too low for visible light.

Solution: Use brightness levels of 25% and above for incandescent lamps.

Brightness Doesn't Match Expectations

Symptoms: 50% looks like 20% or 80%.

Cause: Wrong dimming curve selected.

Solution: Choose curve matching your load type (see section below).

GET and SET Format

Both SET and GET work in the same format:

• SET accepts percent: 0-100
• GET returns percent: 0-100

dimmer.set_level(50)       # Set 50%
level = dimmer.get_level() # Get 50

UART vs I2C — Which to Choose?

UART limitations:
- Recommended interval between commands: 10-20 ms
- More frequent commands may cause buffer data loss
- UART is a relatively slow interface

Recommendation: If you need frequent brightness changes (smooth transitions, animations), use I2C — it's significantly faster.

# UART: no more than 3-5 commands/sec
for level in range(0, 101, 10):
    ser.write(bytes([0x02, 0x53, 0x00, level]))
    time.sleep(0.3)  # Minimum 200-300 ms between commands

# I2C: can be much faster
for level in range(0, 101):
    bus.write_byte_data(0x50, 0x10, level)
    time.sleep(0.01)  # 10 ms — smooth transition

Choosing a Dimming Curve

Which Curve to Choose?

LINEAR (default)

Power
100% │         ╱
     │       ╱
 50% │     ╱
     │   ╱
  0% │ ╱
     └──────────────
       0%   50%  100%
          Level

• Power linearly depends on level
• Universal option
• Suitable for most loads

RMS

Brightness
100% │         ╱
     │       ╱
 50% │     ╱
     │   ╱
  0% │ ╱
     └──────────────
       0%   50%  100%
          Level

• Compensates for incandescent lamp non-linearity
• 50% level = 50% perceived brightness
• Ideal for incandescent lamps

LOG (Logarithmic)

Brightness
100% │              ╱
     │           ╱
 50% │       ╱
     │   ╱
  0% │╱
     └──────────────
       0%   50%  100%
          Level

• Accounts for logarithmic eye perception
• Smooth brightness changes at low levels
• Recommended for LED lamps

Recommendations

⚠️ Important: Gas discharge lamps (halogen, fluorescent, HID, sodium) are not supported — they require high voltage for ignition and maintaining the discharge.

How to change curve:

# UART
ser.write(bytes([0x02, 0x43, 0x00, 2]))  # LOG

# I2C
bus.write_byte_data(0x50, 0x11, 2)  # LOG

Error Codes

Summary Table

Error Handling Example

Python:

ERROR_CODES = {
    0x00: "OK",
    0xF9: "Invalid command syntax",
    0xFC: "EEPROM write error",
    0xFD: "Invalid dimmer index",
    0xFE: "Invalid parameter value"
}

def check_response(resp):
    if not resp:
        return "No response"
    code = resp[0]
    return ERROR_CODES.get(code, f"Unknown error: 0x{code:02X}")

Arduino:

const char* getErrorMessage(uint8_t code) {
    switch (code) {
        case 0x00: return "OK";
        case 0xF9: return "Syntax error";
        case 0xFC: return "EEPROM write error";
        case 0xFD: return "Invalid index";
        case 0xFE: return "Invalid parameter";
        default: return "Unknown error";
    }
}

Compatible Loads

Supported

⚠️ Important about motors:
- ✓ Universal brush motors (vacuums, mixers, drills)
- ✗ Induction/asynchronous motors (most fans, pumps) — will hum and overheat!
If unsure about motor type — don't use dimming.

Not Supported

Lamp Flickers

Symptoms: Lamp blinks or flickers during operation.

Possible causes and solutions:

💡 Note: DimmerLink eliminates software flickering. If flickering persists — the cause is in the load or wiring.

General Tips

Checklist Before Starting

DimmerLink:

☐ Power connected (VCC and GND)

☐ TX/RX connected crossed (for UART)

☐ SDA/SCL connected directly (for I2C)

☐ Pull-up resistors installed (for I2C)

☐ Device in correct mode (UART or I2C)

Dimmer:

☐ Z-C and Dim connected to DimmerLink

☐ Dimmer connected to AC mains (CAUTION!)

☐ Load power doesn't exceed dimmer rating

☐ Load is compatible (see table above)

Minimal Functionality Test

UART:

import serial

ser = serial.Serial('COM3', 115200, timeout=1)  # Or '/dev/ttyUSB0'

# Request mains frequency
ser.write(bytes([0x02, 0x52]))
resp = ser.read(2)

if len(resp) == 2 and resp[0] == 0x00:
    print(f"Device working! Mains frequency: {resp[1]} Hz")
else:
    print(f"Error: {resp.hex() if resp else 'no response'}")

I2C:

from smbus2 import SMBus

try:
    bus = SMBus(1)
    freq = bus.read_byte_data(0x50, 0x20)
    print(f"✓ Device working! Mains frequency: {freq} Hz")
except OSError as e:
    print(f"✗ Connection error: {e}")
    print("Check:")
    print("  - SDA/SCL wiring")
    print("  - Pull-up resistors")
    print("  - Is I2C enabled: sudo raspi-config")