Schematics for GoTo motor controller.

[JorgeST]

I apologize in advance if this is not the right forum.  Please let me know and I will delete the post and place it in the correct forum.

I am in great need of schematics for "motor controller made by "Synta" (aka SkyWatcher, aka Orion), commonly employed in the GoTo Dobsonians.  This particular version is the MC003 Rev. C circa 2010

I had a 'sad' accident with mine and I must replace the uControllers and figure out a bootloader to reload the firmware.

Any help will be  greatly appreciated.  I would prefer not to reverse engineer the entire controller and just get the schematic outright.

Thanks,

[malc-c]

There is no official schematics for Synta control boards, and the ones that have been reverse engineered still have bugs in them and tend to be for the HEQ5 and EQ6 mounts.

Have a read of this thread which covers repairs of synta motor boards, and how to convert the firmware binaries into loadable HEX files and reprogram the two 16F886's.  To save you time you could try the converted file attached. 

Best way to remove the PIC microcontrollers if you don't have a hot air station is to use a dremel with a cutting disk and very carefully cut the legs where they enter the package.  Once the package has dropped away the legs can be carefully removed using a suitable tipped soldering iron, taking care not to lift the tracks.

You will need a PIC programmer like the PicKit2 or above, and an 28 pin SOIC adapter to allow the chip to be programmed.  I use a simple SOIC to DIP adapter and a cloths peg to hold the chip in place

 

Good luck in sourcing the microcontrollers... when I last tried to get a pair the leadtime from my normal UK suppler was 22 months !

 

Hope that helps.....

MC003_V0214_A.hex

[JorgeST]

Thank you Malcolm.  Very grateful for pointing me in the right direction.  I do in fact have access to an entire suite of rework tools. 

The PIC(s) are another story.   Digikey, Mouser, Newark, Future, et. al. show 0 stock. Microchipdirect shows 30 April.  Nonetheless I will reach out to the Microchip FAE and and ask for her help.  Let's see what happens.

The diodes that isolate the Tx lines are also blown.  Those are widely available (1N914) but I will replace them with a small-signal Schottky diode (30V @ 100mA).

There is no reason to drop .70V across at 2mA.  The SD107WS-7-F exhibits only 300 mV at 2 mA when forward biased.

If I repair the controller, I also plan to design a fully bidirectional galvanic isolation stage for it to completely isolate the mount-based electronics from any 'electrical disturbance' (aka self inflicted pain), so this problem NEVER happens again.

I will place PDF schematics, BOM and the PCB Gerbers for everyone to implement, and make it available in this thread.

Did you see my email reply to you about TFS?

Thanks again

[malc-c]

Sounds like you know what you're doing... I used 1N4148's as a replacement on a few boards that had blown diodes.

Not sure how you blew your board, but a while back I came across this isolated EQDIR cable... you might be able to take some of the ideas covered there and use it in your new design.  Looking forward to your project, which I hope you will document on the forum?

Haven't seen any e-mail, possibly send it as a PM...

[JorgeST]

Malcolm,

Thank you for the reply.  I also sent you a Skype invite in addition to the email I sent early Friday January 28 

Best,

 

 

[malc-c]

Drop me a PM with the email address used .  If it was to the micro-heli.co.uk address then that might explain it as that was closed 12-18 months ago... and I've not used skype for years..... 

[JorgeST]

Replied via (what I believe was) the forum's PM

I also got a hold of the Microchip FAE that serves my employer. 

I asked for her help and she say there might be a few lingering around someplace. 

My company expend more that > $400K every year with Microchip so I am sure she'll try to find a few.

I'll keep you informed. 

 

Meanwhile I am putting together the means to program the SOIC package.  

I have the software and hardware tools, also  I just ordered 2 of these: http://www.logicalsys.com/painfo-vpasp-vb.asp?adapter=pa28so1-08-6   to make a programmer

Those are 28 pin SOIC to DIP with a ZIF (Zero Insertion Force) so the PICS can be easily programmed without soldering anything

In the meantime I will start a complete analysis of the original board and I will trace every connection on the board to extract an schematic.  At first glance the MC003 device appears to be  quite simple.

1. It utilizes each PIC16F886' counter timer to generate a variable PWM

2. On half the bridge is used for each motor.  The Inputs 1 and 2 (or 3 and 4) are used to set direction.  The enable gets the PWM which based on duty cycle integrates the voltage applied over the motor therefore providing 'velocity'

3. The 74LS14 (a non inverter Schmitt Triger buffer) interfaces the PIC pins (which cannot supply a lot of current) to the half bridge

4. The LM324 are used as comparators for the encoders (2 for A/B channels at the motor clearly used for velocity and direction - and possibly to detect stalling), and the BIG CHUNKY one which is a simple single-channel in place to provide precise positioning (I imagine it to be either 1024, 2048 ticks or some power of two.  I need to find out the exact tick count for each encoder.  The small ones (at the motors) are easy.  For the big one I have a plan to using a logic analyzer, a small black mask and some MATLAB code

In short, I got really unhappy that Orion is of no help so I decide to do-it-myself.  If they just sell me the board I would move on.  But know I am [removed word]!

The only caveat is the bootloader; but I'd bet even money it is based on the one provided with the CCS compiler.  A little experimentation might be in order.

Besides I get to do some real work again, not just managing 🙂 🙂 

I'll keep you posted.

[malc-c]

I might suggest the moderators merge this thread with the other one I linked to as the two are quite related.

Part of the problem is that these older boards have been sort of "discontinued" and replaced with a new design as the OP in the thread I linked to found out.  A lot of the newer synscan are ARM processor based as well so you have to buy a complete unit rather than just one MC003 or 004 board.

There are also two variations of drive depending on the scope / mount.  DC motors with encoders (mainly dobsonians) and stepper motors (without encoders) - If you do end up designing your own version of these boards, and add better protection against things like inserting the wrong lead in the wrong socket I'm sure there would be a market for it... once the chips shortage has been resolved....

[JorgeST]

All,

The attached PDF has a basic block diagram of an updated board preliminary design. 

Please be mindful that every new design efforts easily goes into 'feature creep' and... then it never ends.  Let us keep it simple.

Main changes are USB input (PC) and handheld controller inputs (self disciplined; if you connect the USB it will ignore the HC).  It will also use a more modern (aka available) motor bridge.

The comparators are shown for clarity but I will not use an LM324 for it.  There are FAR better choices.  Some glue logic is not shown but I will write a Hardware Design Description to explain it all (as time permits)

The power supply will be made far more robust and I assure you I  will make AMPLE provision to design against accidental "screwups" like mine.

Feel free to ask questions.

The overall idea (once I figure the bootloader issue) is that any existing firmware can be loaded into this architecture and function just the same.   I will publish everything under an open source license so no restrictions to use or change/improve

Ideally the PCB should have the SAME dimensions and mounting hole locations and the connectors in the same place with an allowance for the USB probably as a small 4-pin JST or Molex wired to the outside via something like this: https://www.adafruit.com/product/937

I have a real job so progress will not be the same as a full time task but after so many years not doing design but management, this effort will be cathartic 🙂

MC_Block_Diagram.pdf

[malc-c]

Only comment... I would suggest a USB - B type connector rather than a small C type - this is more robust IMO

 

[JorgeST]

Good progress today.  Schematic is almost ready for a detailed design review (see attached). 

Take a look and let me know of any comment, ideas or additions (or subtractions 🙂 )

 

 

MC003_Discovery.pdf

[malc-c]

As mentioned, I'm no electronics expert, just a hobbyist, but here's my comments:

With regards to the micro-USB socket, whilst this is fine for any firmware update, if you continue to apply this to any EQ Mount where the port could be used as a means of control and be permanently connected then a type B USB port would be more suitable.  The only other comment is using a liner 7805 as the regulator for the 5v supply.  Whilst it will do the job there are more efficient alternatives in the same package that employ a switch mode regulation.  More efficient and less heat when reducing 12v to 5v 

[JorgeST]

The intent is to maintain form, fit and function with the existing board.

To that end, the 'tentative' outline of the PCB (and hopefully the connector locations) will be in the same places as the current board.

The same applies for the mounting holes.

Preserving 'real-estate' is a must.

The reason for the micro-USB is that I have no intention of connecting a USB cable directly to the board.

I will use an Adafruit cable that "converts" from micro-USB to USB type B.  I sent a link before.  See it here... https://www.adafruit.com/product/937

I will mount the USB Type B connector on the side of the controller housing.

As per the regulator: the 7805 and in general all analog regulators have two basic drawbacks:

A: Heath dissipation: The analog regulators follow Ohms law and dissipate heat as a product of the voltage drop across the shunt times the current flowing through it.

B: Efficiency:  Actual battery life depends on load current and battery voltage over time. Efficiency is low if the difference between input and output voltages is large (Vin-Vout = 12V - 5V = 7V @ 110 mA)

 

I am using a switching regulator. 

Three reasons:  they do better that linear ones for the reasons stated above.  In this case I selected one with a quiescent current big enough where the efficiency will approach 87%.  Not spectacular but good enough.

The third reason is that the environment is particularly noisy (electrically speaking that is) where I plotted the induced noise spikes of the motors against the baseline noise of a lab power supply and got some 63 dB above the said noise floor.

Does it work anyway?  Clearly.  Can be improved?  Absolutely.  Does it impact the price? Yes! then again I will think is worth it.

Finally it is an isolated converter; thus, the return ground path is not at the POL but at the source, which makes for a significant improvement in EMI and EMC. 

I know most hobbyists do not care but hey! I design avionics for a living.  I am a pain about these things. 😆

The differential mode EMI filter is there to reduce noise at the handheld, thereby the two-by-one decade filter in reverse order.

Since magnetic flux flows inside the ferrite core, common mode choke coils work as an inductor against common mode current. Accordingly, using a common mode choke coil provides larger impedance against common mode current and is more  effective for common mode noise suppression

Thank you for the Synta papers.  I now have what I need to test the interface at will and learn about the protocol.  This is turning to be a lot of fun!  I get to do real work again!

[ozarchie]

Hi All,

Firstly, good luck with the project. The SW design based on PICs has been around for a while. I obtained my first "Upgrade" kit for the Orion EQ6 in ~2004.

While the attached files are EQ6 based, you may be able to get some info from them.

Andrew Johansen has a Syntatester program that will help in debugging your hardware.

You can find him on most astronomy forums.

Cheers

Archie

Schéma électrique eq6 v1.pdf PCDirectCodes Vx.txt Dossier technique v4.0.pdf