AstroLink 4 Pi User manual

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
AstroLink 4 Pi
astrojolo.com @2021

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
Main features:
•Raspberry Pi
*
4 based astroimaging control center
•dedicated AstroLink 4 Pi INDI driver
•focuser motor control for Robofocus, Moonlite, or generic unipolar or bipolar stepper motor
•up to 1/32 micro-stepping control with 2.0A maximum current and 1.4A maximum
continuous hold current
•DS1820 temperature sensor input
•permanent focuser position –no need to park focuser after the session
•2 adjustable PWM power outputs to control dew heaters, telescope fans, or custom Peltier
coolers. The maximum load is 40W per output
•2 switchable power outputs to power mount, cameras, or filter wheels. The maximum load is
5A per output
•1 additional permanent power output
•1 additional adjustable 3-10V output
•XT60 high current input voltage socket
Technical data
•dimensions: 137x83x32mm
•weight: 160g
•the maximum current drawn from all outputs: 10A
•AstroLink power consumption: 6W max
•regulated PWM outputs: 40W max
•permanent 12V DC output: 5A max
•switchable 12V DC outputs: 5A max
•focuser stepper motor outputs: RJ12 6 pin, 2.0A max
•adjustable output: 2A maximum peak load, 1.5A continuous load
•sensor inputs: Jack 3.5mm
*
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WARNING!
Do not connect or disconnect stepper motor when power is on. It may
damage stepper motor controller.
Make sure the stepper hold torque is set to 0% before replacing stepper
motor with motor of different type.
Do not cover ventilation slits at the enclosure sides and back.

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Device overview
System and hardware requirements
AstroLink 4 Pi requires a Raspberry Pi
*
4 module to be installed. Module with 4GB of RAM is
recommended. AstroLink 4 Pi has been designed to work under the control of the dedicated
AstroLink 4 Pi INDI driver, which is available at https://github.com/astrojolo/astrolink4pi . Astroberry
system is recommended, however any working Linux distribution that supports INDI drivers system
will work. Good quality 32GB card is recommended (Class 10 at least). Most of the Raspberry
Pi *problems come from a poor quality power supply or SD card.
PWM outputs
AstroLink 4 Pi has two RCA outputs that provide PWM (pulse width modulation) regulated voltage.
Regulations cover the full 0-100% range. These outputs are usually used for powering dew cap
heaters. Output can be regulated using both controls in the dedicated INDI driver panel and 3rd party
software that supports the INDI interface. PWM cycle period can be set in the INDI driver options in
the range 50-1000ms. Default output value at the connection moment can be defined.
Switchable 12V DC outputs
The device contains two switchable DC outputs, that may provide a supply voltage for imaging setup
components (camera, mount, etc). Output can be switched using both controls in the dedicated INDI
driver panel and 3rd party software that supports the INDI interface. Default output value at the
connection moment can be defined.
Focusing motors control
The focusing motor can be controlled with AstroLink 4 Pi device. The focusing stepper motor can be
connected to the 6 pins RJ12 socket (see Figure 5). It supports 12V unipolar motors with gearboxes
and bipolar motors at any microstepping resolution in a range of full step to 1/32. The focusing
motor can be controlled with a dedicated INDI driver panel and via INDI interfaces. Depending on the
AstroLink 4 Pi revision, the stepper motor current is adjusted with a potentiometer, or in the INDI
control panel. Setting holding power is also possible. For unipolar geared motors it is highly
recommended to set holding power to zero, so the motor will not overheat. Setting 1/8 or 1/16
resolution for the unipolar motor is recommended, so the motor movement is smooth.
Permanent 12V DC output
This output is connected directly to the input 12V XT60 socket. Can be used to provide power to a
mini PC or any other device powered with 12V.
Adjustable DC output
Internal switching converter provides regulated voltage in a 3-10V range that can be used to power
any peripheral devices (DSLR, USB hub, etc.) Voltage can be adjusted with a 2mm flat screwdriver
using a small potentiometer.
Sensors
AstroLink 4 Pi can be equipped with a DS1820 temperature sensor to monitor external conditions.
The temperature reading is available in the dedicated INDI driver panel and can be used to perform
temperature compensation of the focuser position.
*
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AstroLink 4 Pi manual - astrojolo.com
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External view
Figure 1 - external views
1. LAN port
2. USB3.0 ports
3. USB2.0 ports
4. XT60 power input (12V DC)
5. Regulated DC output (3-10V)
6. Regulated RCA outputs
7. 12V DC output (non-switchable)
8. Switchable 12V outputs
9. Temperature sensor input
10. Focusing motor output

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Hardware setup
Raspberry Pi
*
installation
Figure 2 - enclosure screws
Installing the Raspberry Pi*module requires opening the AstroLink 4 Pi enclosure. You need to
unscrew four out of eight screws at the device's sides. Please remove only bottom screws. Then
remove enclosure top. After that, you need to unplug the cooling fan.
Figure 3 - Raspberry Pi module fixing screws
Then remove four screws that fix the Raspberry Pi*module and place the module in the device.
Watch the proper position of the GPIO socket. Put the Raspberry Pi* sockets into the holes in the
front device panel and push the pins down to the GPIO socket. Then fix the Raspberry Pi* module
with four screws, connect the fan (refer to Figure 4 for the fan polarity), and mount the top part of
the enclosure. The last step is to put back four screws at the device's sides.
*
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Setting focusing motor current
Figure 4 - AstroLink 4 Pi interior
If you can see the current regulation option in the Options tab of the AstroLink 4 Pi INDI driver, do
not adjust the current using the potentiometer. It should be left at the factory default 0.4A, that is
0.2V.
Depending on the AstroLink 4 Pi revision you may adjust the focusing motor current at the INDI
driver options panel or use the potentiometer. If you cannot see the current adjustment option in
the INDI driver panel, then the stepper motor current is regulated with a small potentiometer at the
stepper motor controller (see Figure 4). To check the current, you need to measure the voltage
between the adjustment potentiometer wiper and the GND point. Required steps:
1. Unscrew and take off the enclosure top. Disconnect fan
2. Power the AstroLink 4 Pi device
3. Do not login to the astroberry panel and do not connect the INDI driver
4. Measure the voltage
5. Use a 2mm flat screwdriver to adjust the voltage
The motor current can be calculated from the measured voltage with the following formula:
current = voltage * 2
For example, if the measured voltage is 0.6V, then the output current is set to 1.2A. Please refer to
the stepper motor datasheet to set the correct current. The maximum allowed current is 2.0A, but
then the holding current should not be set to 100%. The recommended maximum continuous current
value is 1.4A.

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The default factory value is 0.4A –ready to use by unipolar Robofocus, Moonlite, or AstroLink motors,
and safe for most of the bipolar stepper motors.
The stepper motor socket pinout is presented in Figure 5.
Figure 5 - AstroLink 4 Pi focusing motor output
Required connections are listed in the table below.
pin
unipolar
bipolar
1
COMMON
NOT CONNECTED
2
COMMON
NOT CONNECTED
3
COIL A
COIL A
4
COIL A’
COIL A’
5
COIL B
COIL B
6
COIL B’
COIL B’
Setting the regulated output voltage
The voltage at the regulated output can be adjusted using a small potentiometer at the DC converter
module (see Figure 4). To access this potentiometer you need to take off the enclosure top (see
Figure 2) and then use a 2mm flat screwdriver to adjust the voltage. The regulated output voltage
can be set in the range of 3 to 10V. Use a multimeter connected to the regulated voltage output to
control the actual voltage value.
Disconnect any device from the regulated voltage output before you start the voltage adjustment
operation!

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Software installation
System setup
The recommended software is the Astroberry system that can be downloaded at the site
https://www.astroberry.io/. Astroberry installation procedure is described there in detail. After the
first run, you need to update WiFi settings and connect to the home wireless network and update the
system. Do not remove the default astroberry WiFi hotspot, that is used as a failover if it cannot
connect to any other configured networks.
After that step, two more actions are required. Open Raspberry Pi Configuration and in the Interfaces
tab enable 1-Wire –this is required to read data from the temperature sensor. Then in the
Performance tab enable the Fan section, and select GPIO pin to 13. Then adjust the temperature
when the internal fan starts to work. The recommended setting is 60-70C –to be on the safe side.
When the CPU reaches that temperature the cooling fan will be switched on.
All these actions above are not required when you purchase AstroLink 4 Pi device with the
preconfigured system.
INDI driver installation
AstroLink 4 Pi INDI driver is available at the https://github.com/astrojolo/astrolink4pi page. Required
installation steps are listed in the README file.
Driver installation is not required when you purchase AstroLink 4 Pi device with the preconfigured
system.
INDI driver configuration
The configuration below will be presented for Kstars/EKOS system.
The first step is to create a new hardware profile. Click plus icon next to the profile selector and fill it
with all the equipment you have. As one of the Aux devices select AstroLink 4 Pi. Then click Save.
Figure 6- EKOS profile editor

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After that, you should be able to start the EKOS with the play button, and INDI Control Panel should
be opened. If you close INDI Control Panel by mistake, it can be always opened with the button with
the INDI logo.
AstroLink 4 Pi control panel contains several tabs.
Main Control
Figure 7 - Main Control
Here you can Connect or Disconnect from the AstroLink 4 Pi device using standard buttons.
Focuser info section contains information about step size and critical focus zone. These values are
calculated from focuser configuration data and Telescope device data (aperture and focal length).
If the temperature sensor is connected to AstroLink 4 Pi device, then the Temperature section is
present and the current temperature is displayed here. When temperature reading is available, also
temperature compensation is possible.
General Info tab contains some basing information about the driver. None of these fields is editable.

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Options
Figure 8- Options tab
Configuration –here you can load, save, reset or purge the INDI driver configuration.
PWM cycle –that is the time in milliseconds that cycles regulated PWM outputs power.
Relay labels –these are names of the outputs, that are shown for convenience in the Output tab.
Step delay –time in milliseconds of each focusing motor step. Should be adjusted to the focusing
motor parameters and selected resolution.
Snoop device –that is telescope device name that will be used to retrieve aperture and focal length
data.
Max travel –that is the maximum output position of the focuser. This value is used to calculate the
step size.
Resolution –here required focusing motor resolution can be selected. For unipolar geared motors
1/1 to 1/4 resolution is recommended. For bipolar motors, without an additional gearbox 1/16 or
1/32 is recommended.
Hold power –here you select the holding power of the focusing motor. For unipolar motors, it should
be set to 0 to avoid motor overheating. For bipolar stepper motors should be set to some significant
value, so the balance between the motor temperature on idle and holding torque will be preserved.
Recommended values are 40-60%.

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Temperature coefficient –when the temperature sensor is available, temperature compensation may
be performed. The number of steps per one degree of the temperature change should be entered
into this field.
Temperature compensate –enable or disable temperature compensation. The temperature
compensation cycle is 30 seconds.
Focuser
Figure 9- Focuser tab
Direction –controls the direction of the Relative position move
Relative position –allows moving the focuser by the specific amount of steps
Absolute position –allows moving the focuser to the specific position in steps
Max Position –this is the maximum outward position of the focuser in steps
Abort Motion –stop focusing motor movement immediately
Sync - synchronizes current focuser position to the specific amount of steps
Reverse Motion –reverses focuser motion, so In direction becomes Out. This setting depends on your
focuser mechanics
Backlash –implements backlash correction

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System
Figure 10- System tab
This tab contains several read-only fields with some information about the system. System Ctrl
section allows to reboot or turn off the operating system, but to use these buttons some additional
configuration of sudo is required, so these operations are allowed without a password.

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Outputs
Figure 11- Outputs tab
Outputs tab contains controls for operating with external power sockets of the AstroLink 4 Pi device.
There are three DC 12V outputs in the device. One is permanent, and two are switchable and can be
controlled in this panel. There are also two RCA sockets in the AstroLink 4 Pi that can be used for
powering dew cap heaters. These sockets provide PWM regulation with a long cycle time (the period
can be set in the Options tab) in the range of 0 to 100%.
Default values for the outputs can be saved in the Options tab. Once saved, these values will be
restored on the next connection to the driver.

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Temperature compensation
Temperature compensation in AstroLink 4 Pi is implemented linearly. So there is only one parameter
that describes how temperature affects the focus point. It is not a perfect approach, however, its
accuracy is good enough for most amateur setups.
How to determine the temperature compensation coefficient?
The best way is to note the focuser position at different temperatures. When during session
temperature changes, the focuser position needs to be adjusted to maintain a sharp focus. When you
note these points of temperature and corresponding focuser position, then it is pretty
straightforward to calculate the compensation coefficient, i.e. the number of focuser steps required
to compensate for one-degree temperature change. And this value needs to be entered into the
Temperature coefficient field in the Options tab. When decreasing temperature requires the focuser
position to decrease, then the value will be positive.
How to use compensation?
Once you enter the compensation value into the Temperature coefficient field, you need also to
enable the compensation. Actual compensation is performed once the calculated focuser position
correction is larger than half of the critical focus zone. CFZ value is calculated and presented at the
Main control tab.

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Ground loops
The ground loop in the electrical system occurs when two points that should have the same potential
have different voltages. The ground loop in the astroimaging setup may occur when the ground (i.e.
minus of power supply voltage) is connected to one receiver with more than one cable path. Here
are two example scenarios:
Scenario one
•the newtonian telescope has a mirror cooling fan, and this mirror fan socket is fixed in the
metal mirror cell. Its minus is connected to a metal telescope tube
•the imaging camera case is also connected to the power supply minus.
Now, when you power both fan and camera from the same power supply, then the power supply
ground will be connected to the camera with power supply cable, but also via the fan power socket,
then metal telescope tube, focuser, and camera case.
Scenario two
•an active USB hub is powered from the regulated voltage output from AstroLink
•imaging camera is powered from DC AstroLink output
•the camera is connected to a USB hub with a cable
In this scenario, a negative voltage is supplied to the camera also in two ways. The first one is the
main power cable between the camera and AstroLink. The second loop is from 5V output in AstroLink
to the USB hub and then with the USB cable to the camera.
The ground loop may cause some problems with connections, that are hard to investigate. The best
way is to avoid them. Possible solutions for the second scenario are:
•connect the imaging camera to the computer without an additional USB hub
•power camera from a separate supply
•power USB hub from a separate supply
•do not power the USB hub at all - maybe it is not required
•use a USB cable with galvanic isolation

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Tips and troubleshooting
I cannot find the device in my network
Make sure it is powered for at least two minutes, so it booted up properly and connected to the WiFi
network.
Use some local area network tool to scan and find the IP address of the Raspberry module (like Fing
for Android phones).
Make sure you have updated Raspberry Pi*module WiFi settings properly. If it cannot connect to the
home WiFi network, then it will start as a failover with its WiFi hotspot: SSID astroberry, password
astroberry, IP 10.42.0.1.
If all above fails, then switch off the home router, so there is no WiFi around, and restart AstroLink 4
Pi. After about two minutes it should be astroberry WiFi available, where you can connect.
I have removed the default astroberry WiFi hotspot and now cannot connect at all
You need to open the AstroLink 4 Pi device and:
•remove SD card and reflash it with the fresh astroberry image. Then you will lose all data and
configuration
•remove Raspberry Pi
*
4 module from the device, connect keyboard, mouse, any screen,
power with 5V and 2A power supply, and fix the WiFi configuration
*
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Table of contents
Main features:......................................................................................................................................... 2
Technical data ......................................................................................................................................... 2
Device overview ...................................................................................................................................... 3
System and hardware requirements................................................................................................... 3
PWM outputs ...................................................................................................................................... 3
Switchable 12V DC outputs................................................................................................................. 3
Focusing motors control...................................................................................................................... 3
Permanent 12V DC output .................................................................................................................. 3
Adjustable DC output .......................................................................................................................... 3
Sensors ................................................................................................................................................ 3
External view....................................................................................................................................... 4
Hardware setup....................................................................................................................................... 5
Raspberry Pi installation...................................................................................................................... 5
Setting focusing motor current ........................................................................................................... 6
Setting regulated output voltage ........................................................................................................ 7
Software installation ............................................................................................................................... 8
System setup ....................................................................................................................................... 8
INDI driver installation ........................................................................................................................ 8
INDI driver configuration..................................................................................................................... 8
Main Control.................................................................................................................................... 9
General Info..................................................................................................................................... 9
Options .......................................................................................................................................... 10
Focuser .......................................................................................................................................... 11
System ........................................................................................................................................... 12
Outputs.......................................................................................................................................... 13
Temperature compensation.................................................................................................................. 14
How to determine the temperature compensation coefficient?...................................................... 14
How to use compensation?............................................................................................................... 14
Ground loops......................................................................................................................................... 15
Scenario one...................................................................................................................................... 15
Scenario two...................................................................................................................................... 15
Troubleshooting .................................................................................................................................... 16