MSRC - Multi Sensor for RC - Smartport, XBUS, SRXL

This is a DIY project to send sensors telemetry for a fraction of the weight and cost of the stock sensors. It adds support for several ESC telemetry protocols

Compatible RX protocols: Smartport (FrSky), XBUS (Spektrum), SRXL v5 (Spektrum)

Compatible ESCs: Hobbywing V3/V4/V5, Kontronik, Castle Link

Compatible MCUs: ATmega328P, ATmega328PB, ATmega2560 and ATmega32U4 and Teensy LC/3.x

Implemented sensors:

• ESC
  • ESCs with serial telemetry (Hobbywing V3/V4/V5, Kontronik)
  • ESC with PWM signal or phase sensor
  • ESC Castle Link
• GPS serial (NMEA)
• I2C sensors: BMP280
• Analog sensors: voltage, temperature, current, air speed

All sensors are optional. Make the circuit with the desired sensors and enable them in the configuration, with a lua script if using smartport or in config.h for the rest of Rx protocols

1. Boards

1.1 MCU

MCU	Recommended board	Castle telemetry	UART(1)	Inverted UART(2)
ATmega328P	Arduino Pro Mini(5)	Innacurate	1	❌
ATmega328PB	Pololu ATmega328PB(5)	✅	2	❌
ATmega2560	ATmega2560 Pro Mini	✅	4	❌
ATmega32U4(3)	Teensy 2	✅	1	❌
ARM CortexM0+	Teensy LC(4)	✅	3	✅
ARM CortexM4	Teensy 3.2	✅	3	✅

(1) 2 x UARTS allows to use ESC serial and GPS at the same time
(2) Allows to use hardware serial for Smartport
(3) Arduino Micro is not supported
(4) Teensy LC is not 5v tolerant. If using with Castle is preferred Teensy 3.2, which is 5v tolerant
(5) Arduino Pro Mini and Pololu ATmega328PB requires a USB-TTL programmer for flashing

ATmega boards at 5v (16Mhz) may not read properly serial port when using ESC serial or GPS as they use 3.3v logic level and Arduino 5v. In this case if using 5v it is better without USB (Pro Mini) and/or use software serial. If using ATmega board, is preferred 3.3v (8Mhz) boards

1.2 Connections

Board	Arduino Pro Mini	Pololu ATmega328PB	Arduino ATmega2560	Teensy 2	Teensy LC Teensy 3.x
MCU	ATmega328P	ATmega328PB	ATmega2560	ATmega32U4	ARMCortexM0+ ARMCortexM4
NTC 1	A0	A0	A0	F6(A1)	14
NTC 2	A1	A1	A1	F7(A0)	15
Voltage 1	A2	A2	A2	F5(A3)	16
Voltage 2	A3	A3	A3	F4(A2)	17
Current	A6	A6	A6	B5(A9)	20
Airspeed	A7	A7	A7	D7(A7)	26
ESC serial	RX	RX0	19	D2(RX1)	9
GPS	RX	RX1	17	D2(RX1)	7
PWM in	8	8	49	D4(A6)	6
PWM out	10	10	7	B6(A10)	22
Rx Castle	8	8	49	C7	16
ESC Castle(1)	2 & 10	2 & 22	45 & 48	C8 & B6	22 & 6
Smartport or SRXL	7 & 12(2)	4 & 23(2)	4 & 12(2)	B2 & B4(2) (16 & 8)	0 & 1(2)
XBUS or sensor SDA	A4	A4	20	D1(2)	18
XBUS or sensor SCL	A5	A5	21	D0(3)	19

(1) with pull up 3.3k
(2) with resistor 3.3k

2. Receiver protocol

The following Rx protocols are supported:

• Smartport (Frsky): inverted serial, 57200 bps
• SRXL v5 (Spektrum): serial, 115200 bps
• XBUS (Spektrum): I2C

Depending on the receiver protocol connect to the Rx as follows

Smartport and SRXL

Smartport or SRXL

XBUS

XBUS

3. Sensors

3.1. ESC

Serial telemetry

Compatible ESC serial protocols: Hobbywing V3/V4/V5 and Kontronik

Optionally a PWM signal (PIN 10, 3.3V, 50% duty) can be generated from the RPM value in serial telemetry

ESC serial

PWM signal

If the ESC have a PWM signal or a phase sensor is installed, RPMs can be measured. If ESC have both serial and PWM signal, like Hobbywing V4/V5, then PWM signal is not needed for telemetry

PWM signal/phase sensor circuit

Castle link

The telemetry is send over the ESC signal. Castle Link has to be enabled in the ESC config

If using ATmega328P telemetry values are not accurate all the time. Some readings are increased by 5-10%. This is a hardware limitation

Castle Link with Smartport

Available ESC telemetry

Model	RPM	Throttle	Motor PWM	Voltage	Current	Voltage BEC	Current BEC	Temperature 1	Temperature 2	Ripple Volt
Hobbywing V3	✅	✅(1)	✅(1)
Hobbywing V4/V5(4)(5)	✅	✅(1)	✅(1)	✅	✅(2)			✅ FET	✅ BEC
Castle Link	✅	✅(1)	✅(1)	✅	✅	✅(3)	✅(3)	✅		✅
Kontronik	✅	✅(1)	✅(1)	✅	✅	✅	✅	✅ Power amp	✅ BEC

(1) Available but not forwarded to smartport
(2) For 80A models and higher
(3) Not available in all models
(4) Sensors varies depending on model and firmware. See annex
(5) Upgrade to latest firmware version. But note VBAR versions of firmware are not compatible. Install a non VBAR version of the ESC firmware

If voltage is available the cell voltage average is calculated for 3S,4S,5S,6S,7S,8S,10S and 12S batteries. 10 seconds after power on the number of cells is autodetected. Average cell voltage to be >3.8v for correct cell count

3.2. Serial GPS

Serial GPS (NMEA protocol) is supported

3.3. Analog sensors

The following analog sensors are supported:

• 2 x voltage divider
• 2 x temperature sensors (thermistors)
• Current sensor (Hall effect)
• Airspeed sensor (MPXV7002)

3.4. I2C sensors

I2C sensors not compatible with XBUS. The following I2C sensors are suported:

• Barometer: BMP280

I2C and analog sensors with Smartport

4. Flash to Arduino

Using Arduino IDE copy folder msrc and open msrc.ino. Select the board and flash

5. Configuration

Smartport

The configuration is modified with a lua script (X7, X9, X-lite and Horus with openTx 2.2 or higher)

Copy the file msrc.lua to the SCRIPTS/TOOLS folder. (if using older openTx 2.2 copy to SCRIPTS folder and execute by long press)

If not using lua script comment #define CONFIG_LUA and assign config values in msrc.h

Options:

• ESC protocol. HobbyWing Platinum V3, HobbyWing Platinum V4/Hobbywing Flyfun V5 or PWM signal
• Voltage1. Enable/disable analog voltage divider 1
• Voltage2. Enable/disable analog voltage divider 2
• Ntc1. Enable/disable analog thermistor 1
• Ntc2. Enable/disable analog thermistor 2
• Current. Enable/disable analog current
• Airspeed. Enable/disable analog airspeed sensor
• PWM out. Enable/disable analog a PWM signal from RPM values from ESC serial
• GPS. Enable/disable serial GPS
• Averaging queue size: 1 to 16
• Refresh rate (ms): 0 to 1600
• I2C (x2). Sensor type and address

Other RX protocols

Configuration is done in config.h

6. OpenTx sensors

The default sensor id is 10. This can be changed with change_id_frsky

Depending on your configuration some the following sensors will be available in Opentx. After configuration go to sensors screen and update with Search new sensors

ESC:

• ESC RPM: Erpm (0x0b60)
• ESC voltage: EscV (0x0b50)
• ESC cell average: VFAS (0x0210)
• ESC current: EscA (0x0b50)
• ESC temp FET (HW) or ESC temp linear (Castle): EscT (0x0b70)
• ESC temp BEC (HW) or ESC temp NTC (Castle): EscT (0x0b71)
• ESC ripple voltage: EscV (0x0b51)
• ESC BEC voltage: BecV (0x0e50)
• ESC BEC current: BecC (0x0e50)

GPS:

• GPS Lat/Lon: GPS (0x800)
• GPS altitude: GAlt (0x820)
• GPS speed: GSpd (0x820)
• GPS compass: Hdg (0x840)
• GPS date/time: Date (0x850)

Analog:

• Voltage 1: A3 (0x0900)
• Voltage 2: A4 (0x0910)
• Thermistor 1: Tmp1 (0x0400)
• Thermistor 2: Tmp2 (0x0410)
• Current: Curr (0x020f)
• AirSpeed: ASpd (0x0a00)

I2C:

• Altitude: Alt (0x0820)
• Temperature: T1 (0x0401, 0x0402)

Some of the sensors have to be adusted in openTx

6.1. Adjust RPM sensor (Erpm)

• Blades/poles: number of pair of poles * main gear teeth
• Multiplier: pinion gear teeth

6.2. Adjust voltage sensors (A3, A4)

Measure the voltage of the battery with a voltmeter and adjust Ratio in A3, A4 sensor

6.3. Adjust analog current sensor (Curr)

If using a hall effect sensor, adjust the ratio: 1000 / output sensitivity (mV/A)

To calculate the battery consumption add a new sensor:

• Type: Calculated
• Formula: Consumption
• Sensor: Curr

6.4 Calibrate current sensor HW V4/V5 (EscA)

HW V4/V5 uses few different offsets to measure the current. It have been detected two types, V4 and V5, but there seems to be more types

Current value should be close to 0 A without blades and throttle at 50%. If this is not the case you can calibrate the current sensor (EscA) in opentx (sensor->edit sensor->offset) by adjusting the offset with the value at this condition (no blades and 50% throttle)

7. Images

MSRC on Align 450 connected to Hobbywing V3 Platinum and two thermistors for ESC and motor

8. Video

Video

9. Annex

9.1. ESC protocol specifications Hobbywing

Serial parameters:

• 19200 bps
• 1 packet every 20 ms
• Big endian

Hobbywing V3

Byte	1	2	3	4	5	6	7	8	9	10
Value	Package Head (0x9B)	Package Number 1	Package Number 2	Package Number 3	Rx Throttle 1	Rx Throttle 2	Output PWM 1	Output PWM 2	RPM Cycle 1	RPM Cycle 2

RPM = 60000000 / RPM Cycle

thr, pwm: 0-255 (8bits)

Hobbywing V4 V5

Byte	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19
Value	Package Head (0x9B)	Package Number 1	Package Number 2	Package Number 3	Rx Throttle 1	Rx Throttle 2	Output PWM 1	Output PWM 2	RPM 1	RPM 2	RPM 3	Voltage 1	Voltage 2	Current 1	Current 2	TempFET 1	TempFET 2	Temp 1	Temp 2

thr, pwm: 0-1024 (10bits)

Voltage, current and temperature are raw sensor data. Actual values requires transformation. Depending on the model, sensors are different so the transformations:

• Voltage divider. Different for LV and HV models. LV divisor 11. HV divisor 21
• Current sensor (shunt resistor and diff amp). Different for V4 and V5. V5 seems to be shifted by Vref=0.53V. See 4.4 Calibrate current sensor HW V4/V5
• Temperature. NTC resistor. So far it is the same for tested models

Before throttle is raised from 0, signature packets are sent between telemetry packets. This is used to identify the hardware and firmware of the ESC

Examples:

Model\Byte	1	2	3	4	5	6	7	8	9	10	11	12	13
V4LV25A	0x9B	0x9B	0x03	0xE8	0x01	0x08	0x5B	0x00	0x01	0x00	0x21	0x21	0xB9
V4LV80A	0x9B	0x9B	0x03	0xE8	0x01	0x08	0x5B	0x00	0x01	0x00	0x21	0x21	0xB9
V5HV130A	0x9B	0x9B	0x03	0xE8	0x01	0x0B	0x41	0x21	0x44	0xB9	0x21	0x21	0xB9

9.2. ESC protocol specifications Castle Link

For best accuracy RX pulse input is captured with a timer interrupt and ESC pulse output is produced by hardware PWM. Maximum latency is 20ms

See Castle Link Live

9.3. Output PWM signal for FBL

For best accuracy PWM signal output for FBL is produced by hardware PWM from serial RPM values. Maximum latency is 40ms

9.4. ADC voltage

To obtain the voltage at the analog pin it is required the ADC bits (b) and the Vref:

9.5. Analog voltage sensors. Voltage divider circuit

Two battery voltages can be measured through the analog pins A2 and A3 Metal resistors are recommended as gives more accurate readings (0.1W or higher) Arduino can read up to 3.3V/5V and is optimized for signal inputs with 10K impedance

To select R values apply formulas:

For 6S battery (or lower) and Pro Mini 3.3v:

• R1 68k
• R2 10k

If more than 6S change R values or you may burn the Arduino!

9.6. Temperature sensors. Thermistors

Two temperature sensors can be installed through the analog pins A0 and A1 Temperature is measured with NTC thermistors (100k). Adjust thermistor Beta in ntc.h if needed (NTC_BETA, default is 4190). Sensor output in Celsius

To obtain the thermistor resistance:

And temperature with Beta formula:

Or with Steinhart and Hart Equation if data is available:

9.7. Current

Hall effect

Hall effect sensors. Induced magnetic field is transformed into voltage. They are caracterized by their sensitivity

Shunt resistor

The voltage drop in the shunt resistor is amplified by a differential amplifier to obtain Vo

9.8. Air Speed

Air speed is measured with a differential pressure sensor

Presssure is calculated with the sensor's transfer formula:

And the air speed using the Bernouilli formula:

After 2 seconds the sensor is calibrated to zero

Adjust constants in pressure.h:

• TRANSFER_SLOPE (B) as per sensor datasheet
• For fine tuning measure the Vcc on the sensor and adjust TRANSFER_VCC

10. Change log

0.8

• Added Spektrum Rx protocols XBUS and SRXL V5
• Added support for ATmega328PB, ATmega2560, ATmega32U4, ARM Cortex M0+ and ARM Cortex M4
• Improved accuracy for PWM input (rpm) measurement
• Added support for Kontronik ESC

v0.7

• Added analog airspeed sensor (MPXV7002)
• Fixed Castle Link bug
• Removed BMP180
• Fixed flickering in color lcd displays

v0.6

• Added GPS serial (BN220, BN880, NEO-M8N,...)

v0.5

• Added Castle Link Live protocol
• Hobbywing V4/V5. Improved transformations for voltage and current depending on the model (thanks to Commodore8888)

v0.4.1

• Fix Horus display

v0.4

• Changed R3 resistor to 3.3k
• Support for change_id_frsky to change the sensor id
• Support for I2C sensors
• Improved code quality and performance
• Smartport_library improved performance and abstract from the smartport protocol

v0.3.1

• Added cell voltage average (HW V4/V5, VFAS sensor)
• Applied correct transformation for esc voltage, current and temperature (HW V4/V5)
• Changed averaging type from SMA to EMA
• Added esc protocol NONE
• Smartport protocol. Minor improvements

v0.3

• Esc current sensor (EscA) added (HW V4/V5, 80A or higher)
• Averaging telemetry added
• Voltage2 sensor changed from A3 to A4
• Ntc2 sensor changed from Tmp1 to Tmp2
• Averaging governor added
• Refresh rate and averaging added to lua config script

9. Support

For questions, issues or new protocol request (use this sketch) please post in the forums:

Helifreak

Openrcforums

Or open an Issue in Github

10. Acknowledgements

• Commodore8888 (Helifreak)
• MikeJ (Helifreak)