Recently purchased a used pickup with a AM/FM/CD radio, no auxiliary input. Wanted to listen to my music library while driving. Too cheap to have a new radio install and like DIY projects. Tried several FM transmitters that plug into the cigarette lighter jack. These either quit working within two weeks, could not compete with the ambient FM noise in my area or sounded horrible.
My solution was to place Volumio on a Raspberry Pi 3 with a touch screen. To get the audio onto the radio I used an I2C FM transmitter module based on the KT0803K FM transmitter chip. Since the audio out of a Pi's audio jack is sub-par I used an USB sound adapter.
Built a RF relay to switch the radio's antenna input between the antenna or the transmitter module. This injected the signal directly into the radio. Thus no interference from local radio stations.
Other than a few personalization tweaks to Volumio it went smooth except for configuring the transmitter module. There is very little I could locate to use it with a Pi. All the examples were for Arduino. Inguardians has utility on Github, but it did not include all the features I wanted.
Taking matters into my hand I used the data sheet to write a shell script that can set most of the feature available on a KT0803K chip. Did not include configuration settings for silence detection and associate thresholds. If I ever learn Java, may write a plug-in for Volumio.
Since I had a hard time configuring the transmitter on a Pi I figured others may have the same issue. So, I'm posting the script here for anyone who can use it. It is configured by setting the variables at the upper section of the script. It include description for each variable with range of valid values. Requires ic2-tools to be installed.
#!/bin/sh -e
#
# fmxmtr.set
#
# This script configures configure the Elechouse I2C FM transmitter module V2
# For use with Raspberry Pi
# It shound work with any KT0803/KT0803K based I2C FM transmitter module
#
# Author: Randy Bancroft
# Date: March 31, 2018
#
# No license restrictions
# Use, modify or distribute as you want
# Tested on a Pi 3
#
# Requires i2c-tools
# sudo apt-get install i2c-tools
# For more info on installing and using i2c-tools see link below
# https://www.waveshare.com/wiki/Raspberry_Pi_Tutorial_Series:_I2C
I2C_BUS=1
I2C_ADDRESS=0X3E
# Frequency range is 88.0Mhz to 108.0Mhz for US FM band
# KT0803 and KT0803K chips have a max range of 70.0Mhz to 108.0Mhz
# Frequency range can be restricted by setting FREQ_MIN and FREQ_MAX
FREQ=94500
FREQ_MIN=88000
FREQ_MAX=108000
# Bass boost, minimum=0, maximum=3, default=0
# 0 = Disabled
# 1 = 5dB
# 2 = 11dB
# 3 = 17dB
BASE_BOOST=0
# RFGain, minimum=0, maximum=15, default=15
# 0 95.5 dBuV
# 1 96.5 dBuV
# 2 97.5 dBuV
# 3 98.2 dBuV
# 4 98.9 dBuV
# 5 100 dBuV
# 6 101.5 dBuV
# 7 102.8 dBuV
# 8 105.1 dBuV
# 9 105.6 dBuV
# 10 106.2 dBuV
# 11 106.5 dBuV
# 12 107 dBuV
# 13 107.4 dBuV
# 14 107.7 dBuV
# 15 108 dBuV
RFGAIN=15
# Mute audio, Mute=1, Unmute=0, default=0
MUTE=0
# Mono audio, Mono=1, Stereo=0, default=0
MONO=0
# PGA Mode (Programmable Amplifier), 1dB-increment=1, 4db-increment=0, default=0
PGAMOD=0
# PGAMP, Sets amount of audio amplification (volume)
# If PGAMOD=0 range 0 to 3, default = 0
# If PGAMOD=1 range 0 to 15, default = 0
PGAMP=0
PGAMP_SIGN=0
# Frequency Deviation set the maximum frequency shift for maximum input
# Range 0 to 3, default = 1
# 0 - 00 : 75kHz
# 1 - 01 : 112.5kHz
# 2 - 10 : 150kHz
# 3 - 11 : 187.5kHz
FDEV=1
# Pilot Tone Adjustment, high = 1, low = 0, default = 0
PLTADJ=0
# Pre-emphasis Time-Constant Set, high = 1, low = 0, default = 0
# 1: 50 μs (Europe, Australia)
# 0: 75 μs (USA, Japan)
PHTCNST=0
# Power Amplifier Power Down, disable audio amplifier = 1, enable audio amplifier = 0, default = 0
PDPA=0
# Switching channel mode, disable audio amplifier = 1, enable audio amplifier = 0, default = 0
# 0 = mute when changing channel
# 1 = pa off when changing channel
SW_MOD=0
# Internal audio limiter level control, minimum=0, maximum=3, default=1
# 0 - 00 = 0.6875
# 1 - 01 = 0.75
# 2 - 10 = 0.875
# 3 - 11 = 0.9625
LMTLVL=1
####################################################################################################
# End variable section
####################################################################################################
# Frequency range is 88.0Mhz to 108.0Mhz for US FM band
# Split between three registers
# Bits 11 to 9 are in register 0x01 bit positions 2 to 0 respectively
# Bits 8 to 1 are in register 0x00
# Bit 0 is is in register 0x02 bit position 7
# Set in 100Khz increments
if [ "$FREQ" -gt $(($FREQ_MIN-1)) -a "$FREQ" -lt $(($FREQ_MAX+1)) ]
then
# Divide desired frequency by 50
FREQ_WORD=$(($FREQ/50))
# Split off bits 11 to 9 and store
FREQ_REG_01=`printf "%x\n" $(echo "$FREQ_WORD/512" | bc)`
# Store bits 8 to 0
FREQ_REG_00=$((FREQ_WORD-($FREQ_REG_01*512)))
# Strip off bit 1 to 7 and store
FREQ_REG_02=$(($FREQ_REG_00 & 0x01))
# Shift bit to bit position 7
FREQ_REG_02=$(($FREQ_REG_02 << 7))
# Convert registers to 2 characters
FREQ_REG_00=`printf "%02x\n" $(echo "$FREQ_REG_00/2" | bc)`
FREQ_REG_01=`printf "%02x\n" $FREQ_REG_01`
FREQ_REG_02=`printf "%x\n" $FREQ_REG_02`
# Read registers' current values
# Register 0x02
READ_REG_01=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x01`
# Register 0x00
# No need to read register 0x00, all 8 bits to be written
READ_REG_00=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x00`
# Register 0x02
READ_REG_02=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x02`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x01
WRITE_REG_01=$((0xf8 & $READ_REG_01))
WRITE_REG_01=$(($WRITE_REG_01 | $FREQ_REG_01))
WRITE_REG_01=`printf "%02x\n" $WRITE_REG_01`
# Register 0x00
WRITE_REG_00=$FREQ_REG_00
# Register 0x02
WRITE_REG_02=$((0x7f & $READ_REG_02))
WRITE_REG_02=$(($WRITE_REG_02 | $FREQ_REG_02))
i2cset -y $I2C_BUS $I2C_ADDRESS 0x01 0x$WRITE_REG_01
i2cset -y $I2C_BUS $I2C_ADDRESS 0x00 0x$WRITE_REG_00
i2cset -y $I2C_BUS $I2C_ADDRESS 0x02 0x$WRITE_REG_02
else
# Invalid or no value set
echo Frequency value not set or invalid - skipping
fi
# Base Boost is 2 bits in register 4 at bit positions 0 and 1
# Bit 0 is LSB
if [ "$BASE_BOOST" -gt -1 -a "$BASE_BOOST" -lt 4 ]
then
# Read register 4's current value
READ_REG_04=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x04`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x04
WRITE_REG_04=$((0xfc & $READ_REG_04))
WRITE_REG_04=$(($WRITE_REG_04 | $BASE_BOOST))
WRITE_REG_04=`printf "%02x\n" $WRITE_REG_04`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x04 0x$WRITE_REG_04
else
# Invalid or no value set
echo Base Boost value not set or invalid - skipping
fi
# RFGain is 4 bit split between 3 registers
# Bit 3 is in register 0x02 bit position 6
# Bit 2 is in register 0x13 bit position 7
# Bits 1 and 0 are in register 0x01 bit positions 7 and 6 respectively
if [ "$RFGAIN" -gt -1 -a "$RFGAIN" -lt 16 ]
then
# Split desired RFGain into three register values
# and shift bits to match register's bit position
# Regiseter 0x02
RFGAIN_REG_02=$(($RFGAIN & 8))
RFGAIN_REG_02=$(($RFGAIN_REG_02 << 3))
# Regiseter 0x13
RFGAIN_REG_13=$(($RFGAIN & 4))
RFGAIN_REG_13=$(($RFGAIN_REG_13 << 5))
# Regiseter 0x01
RFGAIN_REG_01=$(($RFGAIN & 3))
RFGAIN_REG_01=$(($RFGAIN_REG_01 << 6))
# Read registers' current values
# Register 0x02
READ_REG_02=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x02`
# Register 0x13
READ_REG_13=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x13`
# Register 0x01
READ_REG_01=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x01`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x02
WRITE_REG_02=$((0xbf & $READ_REG_02))
WRITE_REG_02=$(($WRITE_REG_02 | $RFGAIN_REG_02))
WRITE_REG_02=`printf "%02x\n" $WRITE_REG_02`
# Register 0x13
WRITE_REG_13=$((0x7f & $READ_REG_13))
WRITE_REG_13=$(($WRITE_REG_13 | $RFGAIN_REG_13))
WRITE_REG_13=`printf "%02x\n" $WRITE_REG_13`
# Register 0x01
WRITE_REG_01=$((0x3f & $READ_REG_01))
WRITE_REG_01=$(($WRITE_REG_01 | $RFGAIN_REG_01))
WRITE_REG_01=`printf "%02x\n" $WRITE_REG_01`
# Write new RFGain values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x02 0x$WRITE_REG_02
i2cset -y $I2C_BUS $I2C_ADDRESS 0x13 0x$WRITE_REG_13
i2cset -y $I2C_BUS $I2C_ADDRESS 0x01 0x$WRITE_REG_01
else
# Invalid or no value set
echo RFGain value not set or invalid - skipping
fi
# Mute is 1 bit in register 0x02 at bit position 3
if [ "$MUTE" -gt -1 -a "$MUTE" -lt 2 ]
then
# Shift Mute bit to bit position 3
MUTE_REG=$(($MUTE << 3))
# Read register 0x02's current value
READ_REG_02=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x02`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x02
WRITE_REG_02=$((0xf7 & $READ_REG_02))
WRITE_REG_02=$(($WRITE_REG_02 | $MUTE_REG))
WRITE_REG_02=`printf "%02x\n" $WRITE_REG_02`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x02 0x$WRITE_REG_02
else
# Invalid or no value set
echo Mute value not set or invalid - skipping
fi
# Mono is 1 bit in register 0x04 at bit position 6
if [ "$MONO" -gt -1 -a "$MONO" -lt 2 ]
then
# Shift Mute bit to bit position 6
MONO_REG=$(($MONO << 6))
# Read register 0x04's current value
READ_REG_04=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x04`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x04
WRITE_REG_04=$((0xbf & $READ_REG_04))
WRITE_REG_04=$(($WRITE_REG_04 | $MONO_REG))
WRITE_REG_04=`printf "%02x\n" $WRITE_REG_04`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x04 0x$WRITE_REG_04
else
# Invalid or no value set
echo Mono value not set or invalid - skipping
fi
# PGA Mode is 1 bit in register 0x10 at bit position 0
if [ "$PGAMOD" -gt -1 -a "$PGAMOD" -lt 2 ]
then
# Read register 0x10's current value
READ_REG_10=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x10`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x10
WRITE_REG_10=$((0xfe & $READ_REG_10))
WRITE_REG_10=$(($WRITE_REG_10 | $PGAMOD))
WRITE_REG_10=`printf "%02x\n" $WRITE_REG_10`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x10 0x$WRITE_REG_10
else
# Invalid or no value set
echo PGA Mode value not set or invalid - skipping
fi
# PGAMP is 7 bits split between two registers
# Register 0x01 bits 3 to 5 hold PGA MSB's
# Register 0x04 bits 4 and 5 hold PGA LSB's
# Register 0x04 is not used if PGAMOD is set to 0
# PGAMOD=0 Range minimum = 0 maximum = 3
# PGAMOD=1 Range minimum = 0 maximum = 15
# PGAMP_SIGN, Determines whether the audio is increased or decreased
# 0 = decrease 1 = increase
# Used for both 1dB and 4dB modes
# PGAMOD=0 (4dB increments)
# PGA value amplification
# 0x07 (111): 12dB
# 0x06 (110): 8dB
# 0x05 (101): 4dB
# 0x04 (100): 0dB
# 0x00 (000): 0dB
# 0x01 (001): -4dB
# 0x02 (010): -8dB
# 0x03 (011): -12dB
# Negative values decrease volume
# PGA LSB, Sets amount of audio amplification
# Used for 1dB mode
# PGA and PGA LSB combine to form one register
# PGAMOD=1 (1dB increments)
# PGA PGA_LSB PGA Gain
# 111 11 12dB
# 111 10 11
# 111 01 10
# 111 00 9
# 110 11 8
# 110 10 7
# 110 01 6
# 110 00 5
# 101 11 4
# 101 10 3
# 101 01 2
# 101 00 1
# 100 11 0
# 100 10 0
# 100 01 0
# 100 00 0
# 000 00 0
# 000 01 -1
# 000 10 -2
# 000 11 -3
# 001 00 -4
# 001 01 -5
# 001 10 -6
# 001 11 -7
# 010 00 -8
# 010 01 -9
# 010 10 -10
# 010 11 -11
# 011 00 -12
# 011 01 -13
# 011 10 -14
# 011 11 -15
# check to see if in 1dB (PGAMODE=1) or 4dB mode (PGAMODE=0)
if [ "$PGAMOD" -eq 0 ]
then
# 4dB Mode
# Check if PGAMP is a valid range 0 to 3
if [ "$PGAMP" -gt -1 -a "$PGAMP" -lt 4 ];then
# Shift PGAMP bits to align with bit in register 0x01
PGAMP_REG_01=$(($PGAMP << 3))
# Add sign bit if set
if [ "$PGAMP_SIGN" -eq 1 ]; then
PGAMP_REG_01=$(($PGAMP_REG_01 | 0x20))
fi
# Read register 0x01's current values
READ_REG_01=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x01`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x01
WRITE_REG_01=$((0xcf & $READ_REG_01))
WRITE_REG_01=$(($WRITE_REG_01 | $PGAMP_REG_01))
WRITE_REG_01=`printf "%02x\n" $WRITE_REG_01`
# Write new PGAMP values to register
i2cset -y $I2C_BUS $I2C_ADDRESS 0x01 0x$WRITE_REG_01
else
# Invalid range
echo PGAMP value not set or invalid for 4dB mode PGAMOD=0 - skipping
fi
elif [ "$PGAMOD" -eq 1 ];then
# 1dB Mode
# PGAMP is split between registers 0x01 and 0x04
# Sign bit is register 0x01 bit position 5
# PGAMP bits 3 and 2 are register 0x01 bit positions 4 and 3 respectively
# PGAMP bits 1 and 0 are register 0x04 bit positions 5 and 4 respectively
# Check if PGAMP is a valid range 0 to 15
if [ "$PGAMP" -gt -1 -a "$PGAMP" -lt 16 ];then
# Split desired RFGain into three register values
# and shift bits to match register's bit position
# Register 0x01
PGAMP_REG_01=$(($PGAMP & 0x0c))
PGAMP_REG_01=$(($PGAMP_REG_01 << 1))
# Register 0x04
PGAMP_REG_04=$(($PGAMP & 0x03))
PGAMP_REG_04=$(($PGAMP_REG_04 << 4))
# Read registers' current values
# Register 0x01
READ_REG_01=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x01`
# Register 0x04
READ_REG_04=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x04`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x01
WRITE_REG_01=$((0xc7 & $READ_REG_01))
WRITE_REG_01=$(($WRITE_REG_01 | $PGAMP_REG_01))
# Add sign bit if set
if [ "$PGAMP_SIGN" -eq 1 ]; then
WRITE_REG_01=$(($WRITE_REG_01 | 0x20))
fi
WRITE_REG_01=`printf "%02x\n" $WRITE_REG_01`
# Register 0x04
WRITE_REG_04=$((0xe7 & $READ_REG_04))
WRITE_REG_04=$(($WRITE_REG_04 | $PGAMP_REG_04))
WRITE_REG_04=`printf "%02x\n" $WRITE_REG_04`
# Write new PGAMP values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x01 0x$WRITE_REG_01
i2cset -y $I2C_BUS $I2C_ADDRESS 0x04 0x$WRITE_REG_04
else
echo PGAMP value not set or invalid for 1dB mode PGAMOD=1 - skipping
fi
else
# Invalid or no value set
echo PGAMP Sign value not set or invalid - skipping
fi
# Frequency Deviation is 2 bits in register 0x04 at bit positions 3 and 2
# Bit 2 is LSB
# Frequency deviation adjustment
# 00 : 75kHz
# 01 : 112.5kHz
# 10 : 150kHz
# 11 : 187.5kHz
if [ "$FDEV" -gt -1 -a "$FDEV" -lt 4 ]
then
# Shift bits to match register's bit position
# Register 0x04
FDEV_REG_04=$(($FDEV << 2))
# Read register 4's current value
READ_REG_04=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x04`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x04
WRITE_REG_04=$((0xf3 & $READ_REG_04))
WRITE_REG_04=$(($WRITE_REG_04 | $FDEV_REG_04))
WRITE_REG_04=`printf "%02x\n" $WRITE_REG_04`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x04 0x$WRITE_REG_04
else
# Invalid or no value set
echo Frequency Deviation value not set or invalid - skipping
fi
# Pilot Tone Adjust is 1 bit in register 0x02 at bit position 2
if [ "$PLTADJ" -gt -1 -a "$PLTADJ" -lt 2 ]
then
# Shift Mute bit to bit position 2
PLTADJ_REG=$(($PLTADJ << 2))
# Read register 0x02's current value
READ_REG_02=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x02`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x02
WRITE_REG_02=$((0xf7 & $READ_REG_02))
WRITE_REG_02=$(($WRITE_REG_02 | $PLTADJ_REG))
WRITE_REG_02=`printf "%02x\n" $WRITE_REG_02`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x02 0x$WRITE_REG_02
else
# Invalid or no value set
echo Pilot Tone Adjust value not set or invalid - skipping
fi
# Pre-emphasis Time-Constant Set is 1 bit in register 0x02 at bit position 0
if [ "$PHTCNST" -gt -1 -a "$PHTCNST" -lt 2 ]
then
# Read register 0x02's current value
READ_REG_02=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x02`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x02
WRITE_REG_02=$((0xfe & $READ_REG_02))
WRITE_REG_02=$(($WRITE_REG_02 | $PHTCNST))
WRITE_REG_02=`printf "%02x\n" $WRITE_REG_02`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x02 0x$WRITE_REG_02
else
# Invalid or no value set
echo Pre-emphasis Time-Constant Set value not set or invalid - skipping
fi
# Power Amplifier Power Down is 1 bit in register 0x0b at bit position 5
# It is the only bit used in this register
if [ "$PDPA" -gt -1 -a "$PDPA" -lt 2 ]
then
# Shift Mute bit to bit position 3
PDPA_REG=$(($PDPA << 5))
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x0b 0x$PDPA_REG
else
# Invalid or no value set
echo Power Amplifier Power Down value not set or invalid - skipping
fi
# Switching channel mode is 1 bit in register 0x12 at bit position 0
if [ "$SW_MOD" -gt -1 -a "$SW_MOD" -lt 2 ]
then
# Read register 0x12's current value
READ_REG_12=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x12`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x12
WRITE_REG_12=$((0xfe & $READ_REG_12))
WRITE_REG_12=$(($WRITE_REG_12 | $SW_MOD))
WRITE_REG_12=`printf "%02x\n" $WRITE_REG_12`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x12 0x$WRITE_REG_12
else
# Invalid or no value set
echo Switching channel mode value not set or invalid - skipping
fi
# Internal audio limiter level control is 2 bits in register 0x10 at bit positions 4 and 3
# Bit 3 is LSB
if [ "$LMTLVL" -gt -1 -a "$LMTLVL" -lt 4 ]
then
# Shift bits to match register's bit position
# Register 0x10
LMTLVL_REG_10=$(($LMTLVL << 3))
# Read register 0x10's current value
READ_REG_10=`i2cget -y $I2C_BUS $I2C_ADDRESS 0x10`
# Clear bits to be changed,
# store new value
# and format to two characters to prevent dropping leading zeros
# Register 0x10
WRITE_REG_10=$((0xe7 & $READ_REG_10))
WRITE_REG_10=$(($WRITE_REG_10 | $LMTLVL_REG_10))
WRITE_REG_10=`printf "%02x\n" $WRITE_REG_10`
# Write new values to registers
i2cset -y $I2C_BUS $I2C_ADDRESS 0x10 0x$WRITE_REG_10
else
# Invalid or no value set
echo Internal audio limiter level control value not set or invalid - skipping
fi
exit 0
References
I2C FM Transmitter module
ebay.com/itm/FM-Radio-Trans … 33d702dc1e
I2C FM Transmitter module data sheet
elechouse.com/elechouse/ima … T0803K.pdf
rpi-kt0803k by inguardians
github.com/inguardians/rpi-kt0803k
I2C-Tools tutorial
waveshare.com/wiki/Raspberr … eries:_I2C
USB sound adapter
ebay.com/itm/Laptop-Desktop … 2749.l2649
