BUILD: ARDUINO NANO + NEMA17 BIPOLAR STEPPER 12V 0.4A + EASYDRIVER

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1 BOARD OPTION HW203 DRIVER BOARD The EASYDRIVER v44 driver board which can supply up to 750mA maximum current (typically 500mA), thus is able to driver stepper motors that require more current and hence result in greater torque. The code provided here is for a FULL focuser solution. The Arduino code to use is the code for the DRV8825_HW203 board. The myfocuser Application and ASCOM driver support all driver board options. PRECAUTIONS Never disconnect or connect the stepper motor when the Arduino or External Power is ON. This can result in damage to the driver board The correct method is to first ensure everything is connected then connect the external power 12VDC Disconnect the external power 12VDC prior to disconnecting the USB cable BUILD: ARDUINO NANO + NEMA17 BIPOLAR STEPPER 12V 0.4A + EASYDRIVER The NEMA17PG27 stepper motor (17HS S-PG27, 40Ncm), purchased from omc-stepperonline, operates on 12VDC at 400mA, and is controlled by the EasyDriver v44 motor driver board. A standard NANO R3 mounted on Vero-board is used. The maximum current draw supported by the EasyDriver is 750mA with the stepper requiring 400mA. The Arduino code version to use with this option is FocuservXXX_DRV8825.ino The advantage of using the EasyDriver is that higher torque (more current = more torque) stepper motors can be used. With maximum micro-stepping of 8, a 200 step motor would give 1600 steps per revolution. 1 P a g e

2 TO CONTROL THE myfocuser EASYDRIVER USE THE DRV8825_HW203 CODE AND DRIVERS Software to use for the EasyDriver v44 build Arduino Code Focuservxxx_DRV8825_HW203_XX myfocuser Windows Application myfocuser ASCOM driver Because this board uses micro-stepping, Coil Power should be always ON. Note: Remember NOT to use the Focus Lock Screw on your focuser; leave the screw loose or remove it. The Stepper motor will hold the focuser in place. If you leave the screw in and accidently tighten the focus lock screw, then serious damage can occur to the stepper motor or focuser. MICROSTEPPING The EASYDRIVER board supports micro-stepping which can increase the resolution of the stepper motor (give more steps per revolution). Micro-stepping capability, Full, half, 1/4, 1/8 giving 200, 400, 800 and 1600 steps per revolution with a NEMA step bipolar stepper motor The micro-stepping is controlled by the MS1/MS2 pins of the EASYDRIVER driver board. HOWEVER the current limiting potentiometer must be correctly set else the stepper motor may vibrate or miss steps when stepping. For micro-stepping to work correctly, Coil Power should be ON. EASYDRIVER BOARDS SET CURRENT LIMIT The EASYDRIVER board will need stepper motor current adjustments before being used. The first thing, after verifying the hardware is working and before connecting the focuser to the telescope is to check that the motor is stepping smoothly at the desired step mode setting. a) Connect a multi-meter in series with one of the stepper motor coils, and set to measure current (<1A) b) If you do not have a multi-meter see Note 1 below c) Ensure that the stepper motor is connected to the driver board output d) Connect the controller to the computer via a USB cable e) Turn on 12V supply (motor will not move without an external power source) f) Run the Windows application and connect to the focuser g) Set Coil Power ON and set the stepping mode to FULL steps h) For the recommended motors, the current is set to 70% of 400mA which is 280mA i) Turn the small pot on the driver board till the current reads 280mA j) The stepper motor current is now set Note1: Adjusting the Stepper Motor by using Voltage The EASYDRIVER must be connected to 12v external power and the motor. Measure the reference voltage between ground and the top of the small pot on the driver board. Note that the pot can go round and round and it is remarkably sensitive. Please note that you WILL need to calculate the expected VREF if you are using different stepper types which are not rated at 400mA, or using a different voltage source (not 12V). 2 P a g e

3 Another way to set the current limit is to measure the voltage on the ref pin and calculate the resulting current limit. The current limit relates to the reference voltage as follows: Current Limit = VREF 2 For example, the NEMA17 has a current rating of 400mA. That means = VREF x 2 VREF = / 2 VREF = 0.20 so adjust the trim-pot potentiometer so that the voltage measured on the "ref" pin is 0.2V If you do not have a multi-meter that reads current, you can measure the voltage between the metal part of the pot (what you turn) and GND. At step 9 above, turn the pot till the multi-meter reads 0.2V Note2: Adjusting the Stepper Motor manually It is best to use a ceramic or plastic screwdriver when adjusting the pot. I would suggest a plastic knitting needle which has the end filed down to look like a screwdriver. With the controller connected via USB, and 12V power to the driver board, set the focuser position to 0 and the Motor Speed to SLOW. Now enter a focuser position of 5000 and click the Goto button. Wind the pot all the way anticlockwise until the motor stops moving. Then very slowly turn the pot clockwise until you see the motor start to turn. If the maxsteps is reached, just reset the focuser position to 0 and then type in 5000 for the position and click Goto again. Slowly turning the pot, when you see the stepper start to move ok without jerking, then slowly turn no more than 1/8th clockwise from that point. Then it should be close enough. If you go too far then there will be too much current and the motor will run hot. You should use no more than 12V external power. On some boards clockwise might be anticlockwise. Once set, then switch to 1/4 stepping and repeat the 0 then 5000 Goto. The motor should run smoothly without missing steps (a missed step will be a sudden jerk which you will be able to feel or hear). If there is any of this, you might need to ever so slightly turn it a little more. Be careful as a little turn can make significant changes in current. 3 P a g e

4 myfocuser EASYDRIVER PROTOTYPE BUILD PICTURES Initial prototype and breadboard to test EasyDriver board with NEMA17 bipolar stepper motor and Arduino Uno SCHEMATIC EASYDRIVER-HW203 MINIMAL 4 P a g e

5 LAYOUT EASYDRIVER-HW203 MINIMAL Note: I used prewired 5V LEDS that have a series limiting resistor already provided. It is a simple matter to connect the +ve lead to A2/A3 and the GND lead to GND. Thus in my build, no need for the 470Ω resistors. The LEDS then fit into two 3mm LED Bezel holders that fit to the top side of the case. FIRMWARE FILE TO USE Focuservxxx_DRV8825_HW203_M.ino SCHEMATIC EASYDRIVER-HW203 FULL 5 P a g e

6 LAYOUT EASYDRIVER-HW203 FULL FIRMWARE FILE TO USE Focuservxxx_DRV8825_HW203_F.ino WIRING THE EASYDRIVER BOARD TO ARDUINO 6 P a g e

7 WIRING THE EASYDRIVER BOARD TO RS232 CONNECTOR The EasyDriver driver board has four outputs for driving a bipolar stepper motor. These are connected as shown below NEMA17 Hybrid RS232 Connector Pin EasyDriver Board BLUE 1 B2 GREEN 2 B1 RED 3 A2 BLACK 4 A1 From left to right looking down on the EasyDriver v44 board, A1 - A2 B1 B2 7 P a g e