Print

[pterodyne]

Thinking it might be easier to use an arduino, I looked for any information on the schematics/wiring to do so. I can't seem to find any information.  Does anyone have this info?

Id like to at least prototype and test this and using an arduino while waiting for Tom to get back to the UK during the Holidays...

[TCWORLD]

I must draw a proper schematic for the Mega at some point!

The pin assignments are here (starting at line 37):
https://github.com/TCWORLD/AstroEQ/blob/master/AstroEQ-Firmware/PinMappings.h

Any whose name ends with _0 is the RA axis. Those ending in _1 are the DEC axis.

[pterodyne]

After I posted this, I ordered all the parts to make an astroEQ from Mouser.  I already had a picaxe, and I ordered a AVR programmer. 

The thing Im most concerned about is the circuit board.  I was thinking maybe I could do it on a protoboard. So alternately I could use a protoboard layout if anyone has one of those..

Ill plot it out trace by trace, but obviously it would be easier if someone has it.

Tom, Also, I posted in your availability thread, that I'll take one of the assembled units when you next have them available.

[TCWORLD]

I don't know of a layout that exists already for protoboard, but it shouldn't be too difficult to lay it out from the schematic, just a case of keeping things grouped together - keep all the high power stuff at one side of the board (motor drivers, motor connectors) and double check for short circuits after you solder it to make sure you don't damage anything.

p.s. I saw your post in the availability thread

[pterodyne]

Does the arduino design still use the PIC chip?  I think I understand how to wire the stepper drivers based on the pinouts.  Im not sure how the PIC would be wired in.

[TCWORLD]

No, the arduino design uses the usb-serial chip already on the Arduino Mega. You just need to connect the drivers.

[pterodyne]

Thanks!  I really appreciate you taking the time to answer questions.

I think I have mostly what I need to do this on the arduino.  Ive decided against the DIY board based build for now, mainly because the arduino is easier.  Many might feel that way, do you mind if I post schematics, pics and results when Im done?

Secondly, I'm thinking it would be prudent to put in the capacitors on the inputs and motor side.  Do you suggest that I do all the large electrolytic ones and the small ones?  Or just the 3 Electrolytic, which I assume are for decoupling.

[TCWORLD]

Feel free to post pictures/diagrams!

I would recommend one large electrolytic (100uF) and one ceramic capacitor (100nF) near each motor driver Vmot pin. The electrolytics are good for filtering low frequency ripple which will occur as the motors step, and the ceramics are good for the high frequency noise that the PWM/Current limiting will produce.

[pterodyne]

Thanks!

Can you explain what is the relationship between the gear/step angle etc. settings in your configuration program, and the custom mount settings in EQMOD?  Is your driver presenting itself fully as a HEQ5 or 6?  How does this affect things like PEC, since in my case with a losmandy titan Im thinking of using 12:1 gear on my 3.6 degree stepper, and my worm gear has 270 teeth.  Wouldn't PEC break because it's using the period for a EQ5 or 6?

Also (again sorry for all the questions!) I have the Mega with your firmware configured for my motor/gear/stepper driver specs using your config utility.  Then in eqmod I am connected via maximDL.  NO STEPPER DRIVERS or other hardware connected, just the Mega.  When zoomed in on the star chart, the star moves slightly back and forth in the display.  This never happened that I can recall when I used to have an Atlas mount and eqmod back in the day.  Any thoughts why this might be? I've attached a screenshot from the config utility.  Im only using the values Im using because a guy in Germany sells a stepper kit for the titan which includes the 3.6 degree motor and gearbox combo.  Ultimately Ill probably end up with a 1.8 hybrid stepper with either 1:1 or 2:1 belt drive system.

Thoughts? 

[TCWORLD]

Did you get the DRV8825 Driver boards? If so you need to click the button next to where it says "Motor Driver IC Type" so that it reads DRV8824/5.
You may also want to increase the microstepping mode so that you get better resolution (which should stop the star bouncing around as it were). You could try 1/16th microstepping, if the utility complains then try 1/8th.

AstroEQ presents as a custom mount to EQMOD - the mount settings are stored in EEPROM of AstroEQ and uploaded to EQMOD when it loads. The purpose of the worm gear ratio is to tell EQMOD what you worm teeth are so that it can work out the required PEC settings.
This means you don't need to worry about custom settings in EQMOD, it's all worked out automatically.

[pterodyne]

I have 2 8825 high current, and 2 4988 black editions.  I probably will use the 8825 because of the higher current and voltage ratings.

[pterodyne]

Tom, Ive setup my mega and started wiring the stepper drivers.  Some confusion though on the Pins for Arduino.  I have a sainsmart mega R3 and a true arduino Mega 2560 R3.  Neither have a pin 55 or 54. Is it possible your pin numbers aren't the arduino pin numbers but the chip's pin numbers?

#define resetPin_0_Define 55
#define resetPin_1_Define 54

Secondly you define:

#define statusPin_Define 13

is this for an LED? if so Im suspecting I can omit it.

Thanks!

[TCWORLD]

Ah, sorry, I remember why that happened. I ended up changing all the code so that it doesn't use the Arduino core libraries (save space). I for some silly reason though decided rather than adding some constants, I'd just put the numbers...

54 = Analog Pin 0
55 = Analog Pin 1

Sorry for the confusion.

When I get a spare moment I am going to draw up a proper schematic for the Arduino Mega version.

[pterodyne]

Thanks!

[photo444]

Hi Tom and Pterodyne,  I finally got all the parts including SaintSmart MEGA R3 board.  I have downloaded the firmware and made it connected with EQMOD and Cartes du Ciel.  Thanks to Tom.  Now I am building the circuit and got the same problem of the pin-assignments.  It seems we'll have to wait until Tom comes back. -Paul