astrojolo 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
•Real-time clock embedded (AstroLink 4 Pi version 2 only)
•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: 235g
•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 input: jack 3.5mm
*
Raspberry Pi is a trademark of Raspberry Pi Trading
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.

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
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 or larger 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 signal.
Regulations cover the full 0-100% range. These outputs are usually used for powering dew cap heaters.
Output can be regulated using controls in the dedicated INDI driver panel. PWM cycle frequency can be set
in the INDI driver options in the range 10-1000Hz. Default output value at the connection 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 controls in the dedicated INDI driver panel.
Default output value at the connection 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 the INDI focuser interface. 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.
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 ambient temperature. The
temperature reading is available in the dedicated INDI driver panel and can be used to perform temperature
compensation of the focuser position.
*
Raspberry Pi is a trademark of Raspberry Pi Trading

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
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

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
Version comparison
Feature
Version 1
Version 2
FOCUSING MOTOR CURRENT ADJUSTMENT
With potentiometer
In INDI panel
RTC REAL-TIME CLOCK WITH COIN BATTERY
Not available
Available
RTC battery replacement (AstroLink Pi 4 version 2 only)
AstroLink 4 Pi revision (version) is displayed in the log window after clicking Connect button
CR2032 battery that is used to sustain real-time clock should work several years. If you notice that after
switching on the device time is not set properly it may indicate that battery needs replacement. You need to
open the device (see Hardware Setup section), remove the Raspberry Pi
*
module and you will see the
battery holder. Remove the battery and insert the new one. Make sure the polarity is correct. Refer to the
Software installation chapter for setting up and synchronizing the time.
*
Raspberry Pi is a trademark of Raspberry Pi Trading

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
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 pins. Put the Raspberry Pi* front 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.
To unmount the Raspberry Pi*module just do all these steps in the reverse order.
*
Raspberry Pi is a trademark of Raspberry Pi Trading

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
Setting focusing motor current
Figure 4 - AstroLink 4 Pi interior
AstroLink 4 Pi revision (version) is displayed in the log window after clicking Connect button.
Version 1 only
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.
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.

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
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!
Version 2 only
The stepper motor current is regulated with an option Stepper current in the INDI panel. Do not regulate
the current using the potentiometer –it should be left in the default factory position 0.2V.

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
Connecting temperature sensor
The temperature sensor is a popular DS1820 device. It can be either purchased ready to use or assembled by
the customer. The required connections between the DS1820 sensor and jack 3.5mm plug are presented
below:
DS1820
Jack 3.5mm
GND
Sleeve
DQ (data)
Ring
VDD
Tip
The temperature sensor needs to be connected to AstroLink 4 Pi before the power is on. It will not be
recognized otherwise.

AstroLink 4 Pi manual - astrojolo.com
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Rev. 1.0
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.
If you have a fresh SD card with an astroberry system, then it is worth updating the system with the
command
sudo apt update && sudo apt upgrade && sudo apt dist-upgrade
Download and install required libraries before compiling AstroLink 4 Pi driver. See the INDI site for more
details. In most cases it's enough to run:
sudo apt-get install cmake libindi-dev libgpiod-dev
You also need to enable pigpiod daemon, which is preinstalled with astroberry, but not enabled at startup:
sudo systemctl enable pigpiod
and restart the device. Then you can download and compile the driver:
git clone https://github.com/astrojolo/astrolink4pi
cd astrolink4pi
mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr ..
make