AstroEQ Tutorials Wiki

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Building Your Own Controller

There are two options for building your own controller:


  • (1) Build it around the Arduino Mega (or clone) board, which is fully supported
  • (2) Build a custom PCB using the same design/microcontrollers as the purchased AstroEQs.

There options have different merits. Building with a Mega is easier if you don't have the tools required to make a single sided PCB, or don't want to have a PCB manufactured. However the Arduino Mega uses a poor quality oscillator as a clock source which could mean that tracking speeds are not as accurate as they could be, but if you are using autoguiding, this probably isn't an issue as the guider can correct for this. If you build the custom hardware, it is designed to fit neatly in an enclosure and has a higher quality crystal as a clock source. The down side is you need to either make or get made a PCB, and also need to be able to program the microcontrollers (though these can be bought preprogrammed from the AstroEQ purchase page).


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Building an AstroEQ (Option 1)

Option 1 is using an Arduino Mega. This is probably the simplest option. A schematic is attached below. For this option, you will need some additional components. The values of the required capacitors/resistors can be found in the schematic. The part numbers can be looked up in the tables at the bottom of this page. The circuit is actually pretty much the same as a normal AstroEQ, but with the microcontroller and USB parts removed and replaced by the Arduino Mega.


Arduino Mega Schematic


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Building an AstroEQ (Option 2)

Option 2 is based around a PCB and the ATMega162. I am more than happy for people to make their own controllers if they have the tools required. You will need a soldering iron and also stuff to etch a single sided PCB at home. To help with DIY, I have prepared the following parts list and single sided PCB design files.


The Motor Driver used on the new version of AstroEQ is the DRV8825 Stepper Driver which is capable of providing up to 1.25A without a heatsink. The power input has a protection diode selected as it can run at ~5A continuously, meaning that it shouldn't heat up too much. By using this diode, the board is protected from accidentally connecting a supply with the wrong polarity. Care should be taken when installing the diode to make sure it is the correct way round.


The board should be supplied with no more than 15V DC, and no less than 9V DC. For best performance, a 12V DC Supply capable of sourcing a current of around 4A to 5A.


There is an onboard LM78L05 Regulator to supply the Atmega IC with a regulated +5v supply. As such, if the power is disconnected, the whole board, except for the USB-Serial port will be shut down. This means that you can reset the board by simply unplugging the power. By using an onboard regulator, AstroEQ is compatible with USB hubs which can only supply a small amount of power. The AstroEQ5 board draws <30mA from the USB hub meaning it is fully compatible with bus powered USB hubs.


At the moment, AstroEQ is only capable of driving Stepper Motors, so is not compatible with mounts which use either Servo or DC Motors. Furthermore, only 2 phase Bipoloar stepper motors are supported, however Unipolar motors can be used by leaving the centre tap unconnected, and 4 phase motors can be connected by wiring pairs of phases in series.

github.com_tcworld_astroeq_raw_master_wikifiles_wireconnections.jpg



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Parts List

The following parts are required to assemble the DIY circuit board. Included are values, quantities and Farnell order codes for the parts. You can either buy these from Farnell or use them as a guide as to what parts to buy from your favourite retailer. Many of the parts like resistors and capacitors are not critical and any parts with similar spec will do. The crystals were selected as they have a high accuracy (<10ppm) which makes them ideal for accurately timing the tracking speed.

The PIC18F14K50 and ATMega162 ICs will need programming before use. If you don't have a PIC programmer and AVR programmer, then you can instead choose to purchase just these two ICs pre-programmed from the purchase page.


Resistors:

Qty. Part Name(s) Value Farnell Code Description
5 R13, R14, R15, R16, R19 1kOhm 9342400 MULTICOMP - MF12 1K - RESISTOR, 1K, 0.125W, 1%
2 R18, R20 10kOhm 9342419 MULTICOMP - MF12 10K - RESISTOR, 10K, 0.125W, 1%


Capacitors:

Qty. Part Name(s) Value Farnell Code Description
7 C1, C3, C5, C9, C10, C11, C15 100nF 1100367 AVX - SR205C104KAR - CAPACITOR, 0.1UF, 50V
3 C2, C4, C12 100uF 9451188 MULTICOMP - MCGPR25V107M6.3×11 - CAP, ALU ELECT, 100UF, 25V
1 C6 470nF 1457660 KEMET - C320C474M5U5TA - CAPACITOR, 470NF, 50V, Z5U, 2.5MMP
4 C7, C8, C13, C14 22pF 1100369 AVX - SR151A220JAR - CAP, CERAMIC, 22PF, 100V, C0G/NP0


Crystals:

Qty. Part Name(s) Value Farnell Code Description
1 X1 16MHz 1842217 TXC - 9B-16.000MEEJ-B - XTAL, 16.000MHZ, 18PF, HC-49S
1 X2 12MHz 1842203 TXC - 9B-12.000MAAJ-B - XTAL, 12.000MHZ, 18PF, HC-49S


Connectors:

Qty. Part Name(s) Value Farnell Code Description
1 USB (Connector) USB Connector 1125347 MOLEX - 565790519 - MINI USB TYPE AB, RECEPTACLE, THT
1 PROG Program Header 3418492 TE CONNECTIVITY / AMP - 826632-3 - HEADER, 2ROW, 6WAY
1 J1 Power Jack 1737246 MULTICOMP - MJ-179PH - SOCKET, LOW VOLTAGE, 12V, 5A
2 RA, DEC RJ11 Connector 1560166 MOLEX - 95501-2641 - JACK, 6/4 LOW PROFILE


Case:

Qty. Value Farnell Code Description
1 HAMMOND-1593N 9287566 HAMMOND - 1593NBK - CASE, ABS, HANDHELD, 110X75X25MM


Microcontrollers:

These will need programming, but can be purchase pre-programmed from me through the purchase page of this site.

Qty. Part Name(s) Value Farnell Code Description
1 IC1 ATMEGA162-16PU 9171169 ATMEL - ATMEGA162-16PU - IC, 8BIT 16K FLASH MCU, DIP40, 162
1 IC2 PIC18F14K50-I/P 1648501 MICROCHIP - PIC18F14K50-I/P - 8BIT MCU, 16K FLASH, 768 RAM, PDIP20


Semiconductors:

Qty. Part Name(s) Value Farnell Code Description
1 IC3 78L05 1467367 FAIRCHILD SEMICONDUCTOR - LM78L05ACZX - IC, V REG, 5V
3 PWR, STAT, USB (LED) Red LED 1142499 KINGBRIGHT - L-424HDT - LED, FLAT TOP, 3MM, RED
1 D1 MBR1060 1625119 MULTICOMP MBR1060 Schottky Rectifier, Single, 60 V, 10 A, TO-220AC
1 D2 1N4148 9565124 MULTICOMP - 1N4148. - DIODE, 100V,150MA, DO-35


Driver Boards:

Qty. Part Name(s) Value Pololu Code Description
2 M1, M2 Driver #2133 Pololu DRV8825 Motor Driver board


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Design Files

AstroEQ is open source, and I welcome you building your own controller if you have the means. To do so you will have to etch or have made a PCB on which to solder the components. The list below contains download links to a schematic and PCB layout which was designed to be as easy to home make as possible in that it is single sided. Also included are a to-scale PDF file which can be printed out and used as either a photo mask or for the toner transfer method, along with a second PDF which contains the component legend which can be printed out and stuck to the front of the PCB to help you correctly identify the components.