Volumio for my automobile

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

At first I was happy about an FM radio. But it is a transmitter. :unamused: :laughing:
In any case, a nice project, so you can use the original radio also.

Peziman,
I think this is what you are looking for. It is an I2C FM reciever.

ebay.com/itm/TEA5767-FM-Ste … 0033.m2042

There is a bit more to it than I described above. I designed a holding relay circuit with a 30 second delay after engine off to allow the Pi to shutdown.

I attach the schematic in case anyone wants something similar.
CAR PI_schem.png

I found a typo in my source above under the PGAMP section for writing register 0x04. The mask is set to leave only on bit vice two.

# Register 0x04 WRITE_REG_04=$((0xe7 & $READ_REG_04))

Change 0xe7 to 0xc7 to correct.

# Register 0x04 WRITE_REG_04=$((0xc7 & $READ_REG_04))

Randy

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