Sky9X Mainboard Upgrade

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The sky9x board has been built from the ground up to provide more muscle for the 9x, while using a Atmel SAM3S Arm Cortex M3 32 bit Microprocessor cpu. Easy connectivity is provided for all common mods. Special thanks to Brent Nelson for developing this powerfull board.


All the settings and mods are to be done only running the latest firmware, both main firmware and co-processor firmware.

Where to buy?

The board can be purchased from the projects online store

Board revisions

At the current moment, the board comes in two revision, and a third one is to come:

  • BETA boards - these were mainly distributed through the forum and the developers and the contributers of the original er9x project.
    • At91sam3s2 processor
    • Known issues:
      • Beta boards were based on slightly different processor, the at91sam3s2, for programming the beta board you need a different set of libraries
      • All the Beta boards came with no bootloader on the ATtiny167 co-processor. To get the RTC going, the co-processor needs to be flashed with the bootloader
      • Problem when powering off the 3S LiPol/LiIon, see troubleshooting section for more info

  • REV. B boards. Are no longer sold. Fully compatible with the updated Revision 3 boards.
    • At91sam3s4 processor
    • Known issues:
      • Some boards have unsoldered battery backup pins(unconfirmed)
      • Problem when powering off the 3S LiPol/LiIon, see troubleshooting section for more info

  • Revision 3 boards. Current mainstream board
    • At91sam3s4 processor

Hardware installation guide

The ERSKY9x Board , is a user installable upgrade control board for the 9x series RC Radios.


For a look inside a standard radio, see here

  • It is advisable, to keep your board software(firmware) up to date.


The 9x Forums is a good place to ask any questions you may have, please make sure you're using the latest firmware before you ask any questions.

The White jumper wire , was added to change the Audio Amplifier over from 3.3V to 5V operation , - this helps the Main 3.3V regulator to run cooler , and independent of the volume setting , when using 3S lipos.

The Red wire (if fitted) hooks the original stock buzzer into the board , if you are using the audio output(dedicated speaker) then this is not used, and may be cut(in case you had mods with the stock buzzer, it is advisable to cut/desolder the red jumper wire)

Do not Twist or Bend the Heat sink / regulator , it has been secured to the board , but excessive force could damage the connections ...If you do some how break one , it can be fixed with a small jumper wire ...

Main Board Connections

The image below shows an overview of all the connections for your own personal reference!


Connecting the Stock LCD

The Stock LCD connects to the LCD connector at the top edge of the board. This connector works differently then the one on the stock board. The connector uses a Brown Latch to secure the cable. The ribbon cable is inserted ON TOP of the Brown Lever into the slot. (you will still see some of the Gold contacts on the cable)

Press down on the Brown Lever Tabs on each side of cable. It should lock down the cable in place. To unlock , Pull up gently on each tab , this will unlock and release the cable.



Connecting The Optrex LCD

The Optrex LCD connects to the LCD connector that is set behind where the Stock LCD connects. There is a little Brown level that you flip up with your finger nail it snaps open ... You insert the Ribbon cable , and push down on the lever and it should lock in place.


Mounting the Optrex LCD

You will no doubt discover on installing the optrex lcd that it is not an exact fit.


The Lcd is sitting too high for the board to fit.


Carefully trim the top two corner plastic standoff down to the glass with a sharp knife or side cutters. The plastic is soft and this should be able to be done fairly simply. (Be careful not to apply pressure to the glass corner while doing it)



The LCD now sits just below the height of the standoffs , and the board can be fitted to hold it in place. Note the display still does not sit quite flat and still sits up slightly. This is fine and not visible when mounted, you may want to view how nice it looks when fitted slightly at an angle, before you do any hardware mods to the transmitter case.


The LED Back light Connector has a 200 Ohm surface mount resistor in series with the 5V supply. There are two larger holes on each side of it. This has a 68 ohm resistor mounted on the key switch side of the circuit board. The boards are shipped , with both resistors installed. This arrangement works with the Optrex LED back light , but the The HK back light , needs the 68 ohm resistor removed. A small pair of cutters , can snip it off the board. OR a 150 Ohm resistor could be added in series with the supplied wire harness.

Battery requirements

The ERSKY board is a 3.3V design , it uses "low dropout" 1Amp regulators. It will run fine on any DC voltage, within the range of 6-11 volts. The best results are achieved via 3S LiFe, as it has low self-discharge, and the capacity of the battery is just enough for several flight days on regular radio hardware(long range transmitter, such as Dragonlink UHF, would have significantly more power draw, and the overall battery capacity must be taken into consideration).

  • Powering the board:
    • Use the stock 8AA battery holder and use NiMH or NiCD. DO NOT USE lithium batteries(such as Energizer lithium), DO NOT USE NiZn batteries, AVOID using alkaline batteries.
    • Use 3S LiFe battery, such as widely known HobbyKing radio LiFe battery.
    • Use 2S LiPol/LiIon battery (such as two 18650 cells in series)

It is highly advisable to use a battery that keeps the voltage below 10V, such as a 2S lipo or a 3S LiFe.

DO NOT USE 3S LiPol/LiIon battery. You can use 3S LiPol/LiIon but you have to modify the board(applies to BETA and REVB boards). See the troubleshooting [[1]] for more details.

Telemetry Connections

The Telemetry connection from the FRSKY RF module , connects to COM1 serial port. The connections can be accessed through the 2.5mm Stereo jack. The connections can also be accessed through the 3 Pin header behind the output jack.

The tip of the Jack plug is the TXD The Middle ring is the RXD The Base ring is ground (GND)

You need to make a cross connection when connecting.
That is the TXD of the RF module goes to the RXD of the radio , and the TXD of the radio goes tothe RF Module.

If you wish to use the internal connection. Then a servo extension lead can be used to plug into the 3 pin COM1 connector.

Installing the Mini Din to USB cable

  • Orange Wire – USB Power
  • Blue Wire – USB +
  • Brown Wire – USB -
  • Purple Wire – Ground
Please make sure that the DIN – USB cable is plugged in as shown , You could damage your computer USB port if not fitted properly.


Mounting the Mini DIN Jack


Pull Jack out of slot.


Snip the two leads


Tape leads out of the way , or remove them completely.


Check fit of DIN jack and washer , It should sit behind slot and the metal ring flush with case.

Hot glue or 5 minute epoxy can be used to fix it in place , make sure the glue does not get in the way of the case closing properly.



(also shown is the DIN – USB cable connections. The Yellow / White wires connect the Telemetry Port to the spare connections in the 6 pin DIN connector  , These wires could also be used for other external connections , such as the charger wires.)

Rotary Encoder plugged into Board


The Rotary Encoder can be fitted in place of one of the existing Rotary Controls , or a 1/4” mounting hole could be drilled and fitted were you like. One of the suggested ideas is to mount the encoder on top of the transmitter, in place of a stock FM antenna

Rotary encoder on top.jpg

To get the Knob apart pry the small cap off the top of the knob , and loosen the retaining nut , this will allow the knob to slide off the shaft.

Be careful not to bend the leads coming out of the encoder too many times as they could snap off.

Cabling within the Transmitter case

This shows the overall layout of the two sides of the case with most modifications. Laying out cabling carefully enables the case to be opened fairly easily while only removing one connector. Major mods are described and then more detailed description follows on how they are implemented.

  • the speaker is shown hot glued in at the top.
  • the mini Din connector is shown glued into the left part of the case (this better physically to mount)
  • the frsky telemetry (yellow and white conductors of the mini din cable) are cut and connected to a cable internally to the FrSky DJT module
  • the haptic sensor is at extreme right (some hot glue is needed to hold this; note how two sides of case overlap and it must be inset slightly)
  • (note the rotary encoder is not fitted!)

IMG 0531.JPG

More on FrSky Telemetry

In regards to FrSky telemetry, the text above describes how to connect the mini DIN connector which provides external USB and also wires the ersky9x telemetry through this plug. Alternatively, a 2.5mm jack at the base of the board may be made accessible by drilling a hole through the base of the case. This has the disadvantage of the cable is external and more easily disturbed. An alternative is shown as follows. Cut the yellow and white wires near the mini DIN plug; and use a cable in the case to connect to the telemetry out pins of the FrSky DJT module. (Also note typically when fitting your DJT module, some removing of plastic around the rear of the DJT pin header receptacle is necessary to get the module to sit properly).

This diagram shows the yellow and white conductors traversing across the case from the lower right up to the left side of the rear part of the case. A spare JST connector power cable was connected to this and a hole drilled in the case. Note RxD is connected to TxD and vice versa. Board pinout is shown in PCB at top of this page.

The picture below shows the rear view of the case with the JST connector (slightly filed down) connecting in snugly. Low risk of this being disturbed; hole in case also visible.

IMG 0530.JPG

To configure your Telemetry, please see this forum post.

Bluetooth Modules:

Bluetooth allows received Telemetry information to be distributed via Bluetooth to other devices such PC/Phone etc. As detailed in the Bill of Materials, there are at least a couple of compatible modules - one known as the 'RN-42', and another labelled on circuit board as 'JY-MCU'. Both are available on ebay; try searching on 'Wireless Serial 4 Pin Bluetooth RF Transceiver Module'.

Your bluetooth module should come with a ribbon cable; please note pinout as shown on RN-42 picture below. The pinout for the ersky9x is also labelled on the motherboard (see top image in this guide). The bluetooth connector sits at the lower left of the ersky9x board. RN-42 a.jpg

This picture shows the JY-MCU Bluetooth module and also the connection to the ersky9x motherboard.

IMG 0524.JPG

There is a location on the ersky9x main board to mount a Bluetooth module it is designed for the RN-42 and space is limited. It is not reccomended to install the RN-42 module on the ainboarditself(via the available solder pads), as in case of failure(it was reported) - the module removal maybe troublesome, in the REV.3 board the RN-42 solder pads are removed. An alternative is hot glue it as shown below on the opened radio - glueing it on the rear of the battery compartment; making note of when the case is closed; not to foul the header for the telemetry or other circuit board items. Also note glueing the Bluetooth module such that the pinout is still visible - which enables checking of connections are correct.

To test the Bluetooth module; best to first have Telemetry operational and have data being shown on the main display. Then try to configure and test bluetooth.

To configure:

  • Set the baudrate of the ersky9x to 115K in the min config menu (which is a higher speed than the FrSky telemetry speed)
  • As long as the radio is powered on before a bluetooth connection is made i.e. before it is paired; the ersky9x software will attempt to set the baudrate of the Bluetooth module. Turn on and off the radio after setting the baudrate.
    • Typically modules are nominally set to 9600. Others may vary. Alternatively, a separate USB to TTL converter can be used (or equivalent device). Instructions are here. Also try this.
  • enable bluetooth streaming (BT Streaming) in page 11 of the model config menu

Note if you are not using the Bluetooth module it shouldn't draw much current. It consumes approx 35 mA in the search mode; about 8 mA when radio installed and functioning; and in sleep mode <1 mA.

There are a few Applications capable of receiving telemetry information Connect as normal to a new Bluetooth device using your Bluetooth PC/Phone and looking for advertised Bluetooth devices. Your Bluetooth module will by default show up asJY-MCU / RN-42 typically. Password is typically 0000 or 1234. The name may be personalized (see the configuration information at the Open Pilot Wiki).

# Type Description Link
1 PC Application FrSky Config for Telemetry Transmitter
2 Andriod Phone App FRS Logger
3 Andriod Phone App Andriod Dashboard

Installing RTC battery

The RTC itself if working on a co-processor chip, attiny 167. To get the RTC going - the co-processor needs to be flashed (see the software installation below). If there is no battery installed - the clock will reset itself every time you switch off the radio, so it is advisable to install the battery.

  • For ease of use, ease of connections - solder 3pin header to the board(not necessarily, but it is easier to use it this way)
  • There are two options - use the rechargeable battery, or use "coin type" battery, the rechargeable battery is not the best choice, as with simple CR2032, the RTC will keep going for over two years.

Coin battery installation

  • Install a pin header onto the board

3PIN header.jpg

  • The polarity for battery installation is as in this diagram


  • Make a connection from the battery, either etch a small PCB for the battery holder, or just solder two wires directly to the battery holder. One of the places to install the battery - is on top of the radio.

Battery installed.jpg

NOTE!  Do not attempt to solder a wire directly to the coin type battery. They are heat sensitive and will go BANG!

Installing Aurora9 gimbals

If you wish, you can further upgrade you radio, by installing the Aurora 9 gimbals. They can be easily obtained on site. Installation on the stock board can not be recommended, as the stock board lacks the required ADC resolution to work correctly with these, though there are solutions, they are not an "easy fix", more info here [2], in short - you will need to build an opamp circuit to compensate the range, for the gimbals to be usable on the stock board. On ErSky board - the ADC resolution is high enough, and it works correctly with theese gimbals "out of the box", although some tinkering is required to install them nicely. Installation is pretty simple - all you need is some sandpaper, some files, and M3 bolts and nuts. After removing the stock gimbals - you will notice that Aurora 9 gimbals wont fit, the sizing is a bit offset. With some sandpaper, and a minute or two(really fast, really, the 9x plastic is a soft and easy material to work with), sand the holes for the Aurora9 Gimbals to fit. You may find, that you may need to cut away little "tabs" on the gimbals itself. It can be done with a dremel in a second. NOTE: Potentiometers must be facing the "outer" wall of the radio, otherwise you won't be able to install the trimming knobs. To fix the gimbals in place - use M3 bolts and some large M3 washers - works perfectly, to further lock the gimbals in place - you may use some hot glue, although it is not necessary.


View form the front side


All the neccesary connections can be done by cutting away the stock Aurora9 connector from the gimbals, and soldering the gimbal wires directly to the 9X gimbal distribution PCB. The correct solder order is shown below. The wiring diagram displays clearly how things should be connected. You MAY short the solder points and corresponding wires marked with an oval, this way the soldering is easier

Aurora stick wiring simple.jpg Left-gimbal.JPG Right-gimbal.JPG

For the tidier look from the front, it can be reccomended to use some SUGRU [3] to fill the gap between the case and the newly installed gimbal, the color match is incredibly identical.

After the installation - modify the setting "Gain". This setting increases the ADC gain, and allows to use increased resolution of the Aurora9 sticks.

Ersky r114 gain-setting.JPG

Software installation guide

Using USB for programming and/or as a mass storage device

  • After pluging in the USB, first ten(10) seconds are for programming with SAM-BA
  • Ten(10) seconds later - the second mode kicks in, and USB mass storage begins to work.

Installing SAM-BA programming software and flashing ErSky

Firmware: There are two different types of firmware needed - the main processor firmware, and the co-processor firmware. Both can be updated separately, there is NO need to flash both firmwares everytime, you can always flash just the updated one(most commonly you will find yourself in need to update the main processor firmware)

For programing your radio you need the SAM-BA programming software even if you will use other ways to program the board (Companion9x), as it will still need SAM-BA to be installed.

  • Download and install the SAM-BA program. You must also instal the USB drivers that come with it.

Installing unsigned ATMEL drivers in Windows 8 x64

Windows 8 prevents installation of ANY unsigned drivers, so you will not be able to install the driver directly, but there is a way:

  • From windows 8 right hand menu(when mouse is at the top right corner) choose Settings -> Change PC settings –> General -> Advanced Startup –> Restart now.
  • After some time you will be prompted with a menu with following options.
    • 1. Continue
    • 2. Troubleshoot
    • 3. Turn off

Choose "Troubleshoot"

  • In the next menu
    • 1. Refresh your PC
    • 2. Reset your PC
    • 3. Advanced Options

Choose "Advanced Options"

  • In the next menu:
    • 1. System Restore
    • 2. System Image Recovery
    • 3. Automatic Repair
    • 4. Command Prompt
    • 5. Windows Startup settings

Choose "Windows Startup Settings" and then click "Restart"

  • When the computer restarts, a menu will appear, you must choose option "7", "Disable Driver signature Enforcement". After that the system will boot regulary, and you will be able to install the AT91 USB to Serial Converter driver.

Configuring SAM-BA and flashing the software

  • Overview
    • Firmware consists of basically two pieces of software: main processor firmware + co-processor firmware
      • There is no priority which must be flashed first
    • You need SAM-BA pre-configured to use this specific board and processors configuration
    • DO NOT lock the chip. If you've locked the chip - the radio will work fine, but you will not be able to flash the newer firmware until you erase the chip via the jumper(see troubleshooting)
      • You should not be afraid of chip erasing - all the settings, models, etc, are stored on a separate memory module, chip erasure procedure will only erase the firmware, after flashing the new firmware - the models and all the settings will stay in place

  • Now that you have SAM-BA program installed, you need to go the folder(something like C:\Program Files (x86)\Atmel\sam-ba_2.12) where it is installed. Now locate the tcl_lib folder, and save SAM-BA libraries file in it.
  • unzip the file in the tcl-lib folder, it should rewrite the "boards.tcl" file, and create an new folder called at91sam3s4-9x
  • Now if you run the SAM-BA program you should see "at91sam3s4-9x" in the selection menu.

SAM-BA startup.jpg

SAM-BA main screen.jpg

  • To Load a new version of the software, you enter the New file name in the "Send File Name" Box and click the "Send File" button. - You should see the file upload in the dialog box at the should only take a couple of seconds to program. After its done programming, it will come up with a Lock option. Select the "No" button(if you accidentally pressed "yes" - go to the troubleshooting section and erase the chip). Disconnect the system, close SAM-BA. Connect the board and go to programming the co-processor.
  • To load a co-processor utility, you must select the co-processor tab, execute the "enable co-processor" script, and load the latest co-processor utility. To load the utility, get the latest TinyApp.bin and load it using 0x80 as your start address on the co-processor tab. To check the correct version of the utility - switch the radio on - press LONG up, and under "co-processor" you will see the version. You should see 103 or more(every version upgrade enhances the number) (101 is the stock version)

SAM-BA co-processor programming.jpg

  • After you are done programming , terminate the SAM - BA program. Then you can disconnect the Board.

The SAM-BA program only works the ONE time , You must EXIT it , and re-insert the USB , THEN run the SAM -BA program.

  • YOU Must follow this procedure if not, then you are going to have trouble with the SAM - BA program. And you will get strange Error Messages.

Note! The companion9X program can beconfigured to program the firmware for you. This is done my telling companion where the sam-ba.exe file is on your computer.


Flashing the locked or "bricked" ErSky board


You will have to follow the following procedure in one of the two cases:

  • You have accidentally locked the chip in SAM-BA
  • You have "bricked" the system by uploading a corrupted BIN, and/or accidentally uploading the wrong file.
  • Something went wrong while updating the co-processor

General information

In case of incorrect flashing, when the firmware flash has been corrupted, you need to erase the flash, and reprogram the board. Or you could of locked the chip, after accidentally pressing the "lock the chip" dialog box in SAM-BA.

Recovery instruction

To do the chip erasure procedure - power off, short the "reset/erase" pin with a jumper, power on, and off again. Below is the location of the ERASE pin(note the jumper added for convenience)

Erase pin.jpg

Remove the jumper, and power the board WITH A USB CABLE, other ways of powering the board will not work(if you modified a board, and removed the R49, FIRST plugin the USB, then switch on the power). When powered - the board enters the USB loader state, and though there are nothing on a screen, you will be able to program the board via SAM-BA, program the board, and then execute the Script using SAM-BA - select "Boot from Flash (GPMVN1)" and click "Execute", as shown below

Boot from flash.jpg

After chip erasure procedure - all the settings and models REMAIN. They are not stored in the chip. Though it is advisable to double-check the model settings, after such a procedure.

Powering the system with 3S LiPol/LiIon


In general - it is not recommended to power the system with 3S LiPol/LiIon. On some conditions(inside the case has to be very hot, and 3S LiPol has to be fully charged) the radio may unintentionally enter USB mode, and lock up the radio control. This happens due to the reverse current leakage through the diode, which is used when the system is powered via USB.

General information

  • To power the system off the 3S LiPol/LiIon battery you will have to remove R49 (see the illustration below)
  • After removing the R49, you will have to power the system manually(!) when programming or using the system in usb mass-storage mode

Modification instruction

R49 (10ohm) resistor has to be removed to use 3S LiPol/LiIon battery. Actually you can remove the diode instead.. Remove whichever is the simplest.

R49 removed.jpg

R49 resistor.jpg

Bill of Materials

There is a range of items which are needed to build a Sky9X radio. The table provides a guide to typical components; other mods are being created and are documented in the forum.

# Name Approx $US (ex Shipping) Description
1 9x Transmitter (Turnigy 9x or equivalent) $60 Source: Many R/C retailers (e.g. Hobby King Turnigy 9X “9Ch”& 8ch Receiver). May be purchased without TX and RX if FrSky used.
2 Ersky9x Main Board

Options: Optrex LCD, DIN cable, Rotary Encorder

See: From From and check prices there.The Ersky9x is the core part of this upgrade. The optional Optrex LCD significantly improving the display readability and is backlit. The DIN cable is optional. As an alternative a hole may be drilled in the bottom of the case to access the USB connector on the motherboard. The optional rotary encoder allows for easier changing of values; as an alternative a rotary encoder as below Item 4) may also be fitted.
3 Alternative TX/RX e.g. FrSky DJT $40 Optional. FrSky DJT provides longer range (up to 1.5km nominally) , failsafe, telemetry and other features compared to default TX/RX in 9x. Source: Retailers of Note: Ersky9x board fully integrates FrSky Telemetry
4 Front panel round arrow keys’/ rotary encoder/ select button & Mounting board *New* $7 + $10 Rotary Encoder : Sources: : Part Number: TSWB-3N-CB222 , TSWB3NCB222LFS, TSWB3NCB222LFS

Mounting Board: See Rotary Encoder for sourcing: Mounting Board with pins replaces momentary action switches on ersky9x board and allows mounting of encoder.

5 Bluetooth Module $8 Optional. Good for separate apps e.g. Android FrSky Dashboard to transmit telemetry from FrSky transmitter/receiver. Source: Ebay. Search for Wireless Serial 4 Pin Bluetooth RF Transceiver Module RS232 RM245 or equivalent RN-42. Forums Bluetooth Thread.
6 LiFe Battery 1500mah $7 Optional. HobbyKing Life 1500mah 9.9V or equivalent. Drop in replacement for 9x 8 AAA batteries. Better than Lipo in run flat situations and LiFe has low self discharge rate. Battery modification guide is here
7 Haptic Sensor $5 Optional: Vibrating Device to provide tactile feedback. Source: Ebay or other. Search for 3V Pancake Vibrating Vibration Vibrator Phone Pager Coin Motor. Forums
8 Ersky9x Software $0 See the Forums. Generic er9x Software guide. Note ersky9x software has some enhancements; see forums for more details.
9 Aurora 9 Gimbals $42 a pair Optional: See the [4]. Gimbal installation is pretty straightforward, and the overall quality feel of the TX increases drastically, smoother operation.
10 RTC battery $1-3 Optional: You need to supply addtitional battery for the RTC(clock) to work, without it - every time the time will reset. Ersky firmware r116 and above.

Using the ersky9x board - for a total of $200 - $350 one can build a very sophisticated radio depending on desired features.

Other boards

If you dont like the sky9x board, you could always try the gruvin board

Gruvin9X Mainboard Upgrade