In this section you'll find all the information you need to know to build and flash Ardufocus into your Arduino board.

Build instructions ASCOM Driver


If you have built the Moonlite compatible version then a capacitor is used on the Arduino’s reset line to keep it high during serial connect/disconnect which is mandatory for normal operation but in order to flash the firmware to the board the capacitor must be disconnected, otherwise you need to synchronize a manual push of the reset button when uploading to the board. Once again, this is only necessary if you have built the Moonlite compatible version.

To enable a feature remove the comment tag // from the start of the line. To disable a feature add the comment tag // to the start of the line or delete the entire line.

// The option bellow is ENABLED
#define COOL_FEATURE_6000

// The option bellow is DISABLED
//#define COOL_FEATURE_6000

Config options


Persistent memory

Enable auto save of the focuser position uppon finishing each move. When active the focuser will remember between power cycles the exact position where it was.

#define USE_EEPROM

Remote reset

Remote reset is a non standard feature added to the Moonlite protocol which allows you to reset the micro controller inside the focuser. Please test this feature on your bench before deploying on the field. For this feature to work the default boot loader may need to be changed otherwise the uC will enter into an infinite loop state.


Serial DTR reset (beta)

Enable a subset of commands to control the status of the DTR auto-reset feature on the Arduino boards. By default Ardufocus uses a cap between the reset pin and ground to prevent the DTR signal to reset the board, which happens every time a new serial connection is open to the board. By having the cap between the reset pin and another board pin, enabling this feature allows the DTR auto-reset to be controlled. This is useful for firmware uploads, if the DTR auto-reset is disabled the user must manually press the reset button when uploading new firmware.


This is the board pin which controls the enable/disable of the feature.


Activating this option will enable high resolution counters (32-bit) thus becoming incompatible with the standard Moonlite protocol. You should enable this if using a gearbox or having a millimetre threaded rod on the drive mechanism.


Motor configuration


You should only enable ONE of the following drivers The ULN2003 shall be used with the unmodded version of 28BYJ-48 or any other Unipolar stepper motor. The A4988 driver should be used with Bipolar stepper motors or the modded version of the 28BYJ-48, for more information see the hardware section.

#define MOTOR1_USE_A4988_DRIVER


Tells the firmware which pins should be used to control the driver.

//                    MS1, MS2, MS3, SLEEP, STEP, DIR
#define MOTOR1_PINOUT  12,  11,  10,     8,    7,   6


Activate the following directive if you’d like to invert the motor rotation changing the focus direction.


Sleep when idle

When active Ardufocus will cut the stepper motor current when idle, in theory this could lead to less accuracy between movements but will keep the motor cool. When disabling this flag make sure your motor does not overheat.


Sleep timeout

When the previous directive is active, allows you to control the amount of time the driver will wait, after stopping, before powering down the motor. The idea behind is the system needs full accuracy between the AF point sequence but can be powered down between AF runs. Thus you should set this to wait a bit more than the time your system needs to take and measure each AF point.


Speed profile

Specify a custom speed profile for you motor model and driver combo. The units are in steps/sec.

Usually a motor such as the 28BYJ-48 need lower speed limits:

  • Max speed: 250
  • Min speed: 25

NEMA17 motors allow you to use higher speed limits:

  • Max speed: 1000
  • Min speed: 250
#define MOTOR1_MAX_SPEED 150
#define MOTOR1_MIN_SPEED  25

Acceleration profile

When active Ardufocus will apply the selected acceleration profile to the motor’s speed. The objective is to help the system cope with heavier loads such as FF + FW + CCD combos.


The acceleration profile, independent of the method used, has at least two main periods: the ramp-up period when the motor is gaining speed and the ramp-down period when the motor is losing speed. This setting controls the duration of each one of those periods, the default value is 250 steps for each period if left undefined.

#define ACCEL_DURATION 250

When acceleration control is active this setting controls the minimum required number of steps on a movement for the algorithm to kick in. Any movement with less steps than this will be done at minimum speed without any acceleration control. The default value is 10 steps of left undefined.

#define ACCEL_MIN_STEPS 10

Temperature sensor

TODOExplain howto fine tune the values bellow.

#define NTC_ADC_CHANNEL          0
#define NTC_NOMINAL_TEMP      25.0F
#define NTC_BCOEFFICIENT    3950.0F
#define NTC_NOMINAL_VAL    10000.0F
#define NTC_RESISTOR_VAL   10000.0F

Minimum value to be considered a valid reading (xxxC)

#define NTC_MIN_RAW_VALUE  50

Maximum value to be considered a valid reading (-23C)

#define NTC_MAX_RAW_VALUE 950

According to the Moonlite protocol the temperature probe should only be read when the command :C# is received but some applications, such as SGP, seems not to respect this and only call the get temperature command :GT# which means the temperature will never get updated and the last read value is always returned, either it is valid or not. Enabling the following option will force the temperature gathering process on every temperature read command.