Announcing the ORDuino !

Topics Related to the ORD Bot Printer

Re: Announcing the ORDuino !

Postby frob » Wed Mar 07, 2012 4:22 am

Enraged wrote:how many thermistors can it take? if it can use 3, that would let you control temperature on 2 hot ends and a heated bed.
for the LCD, are you planning to use I2C?
3 thermistors and 4 thermocouples.
The thermocouple circuit and the DAC's are read/written via I2C - the LCD interface is SPI-like, though you can only send not receive - it will thus share the SPI port with the SD card.
Last edited by frob on Wed Mar 07, 2012 5:00 am, edited 1 time in total.
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Status update & board layout preview....

Postby frob » Wed Mar 07, 2012 4:30 am

PS on the thermocouple inputs,
i'm using a separate high-resolution, low-noise sigma-delta ADC (18 bits) with programmable preamplifier - and a high-rez digital temp sensor for cold-junction compensation. In theory that gets you 0.05 deg C resolution and +/-1deg C accuracy.
Thus this would also make a dandy reflow oven controller :D
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Re: Announcing the ORDuino !

Postby naPS » Wed Mar 07, 2012 8:08 am

Is there an easy way to change out the stepper drivers? Blowing these things up is a fairly common occurrence for folks new to CNC.
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Re: Announcing the ORDuino !

Postby StigOE » Wed Mar 07, 2012 12:42 pm

There are pads for installing regular Pololu/Stepstick drivers if the onboard driver fails.
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Re: Announcing the ORDuino !

Postby frob » Wed Mar 07, 2012 12:54 pm

naPS wrote:Is there an easy way to change out the stepper drivers? Blowing these things up is a fairly common occurrence for folks new to CNC.

Yes -
Though it will take slightly more manual dexterity and care than with boards that use modules to begin with;
its a 2 step process :
1- isolate the dead chip by carefully cutting the tracks going to it with an exacto knife - you'll probably need a magnifying glass , or a 10x microscope is even better- and a steady hand :)
2- install the headers in the holes (solder) for the module footprint on either side of the driver IC in question - and plug in the module as customary.

On the other hand, it should be a lot less commonplace to accidentally blow up an IC on my board without gross negligence.
From what i've read one of the most common ways to destroy the pluggable modules is plugging them in backwards or not correctly aligned on the right pins ;
- with on-board drivers, such mishandling issues are thus avoided.
- I use the most recent driver IC's with built-in overload protection.
- the motor voltage bus is protected from over-voltage and reverse polarity - and fused
- much improved thermal design vs what you can provide with modules means overheating should never happen.
- using the DAC option vs potentiometer and avoiding shorting jumpers nearby (using remote dip switches )
also means now there's no reason to go poking around there with a screwdriver while the thing is powered, which is another great way to blow up your board.
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Thermistors and thermocouples ?

Postby frob » Wed Mar 07, 2012 1:12 pm

It occurs to me that it might be better to have the 3 thermistors and 1 thermocouple on the same 8-pin terminal block (the one on the right side)
and leave the other 3 optional thermocouple channels and the RS-485 port on the terminal block along the bottom right edge instead. what do you think ?

That way the last terminal block on the bottom right is only for optional and seldom used stuff that most people wouldn't use, leaving the total board height minimal in the "economy" version; Also moving the thermocouple circuitry a little further away from the motors drivers can only help to reduce noise and heat contamination from them.

Also there's no provisions yet for user inputs like emergency stop or cursor buttons for the LCD, but there might be room left to include that so if you'd like that please tell me exactly what you want and i'll try to include it.
Probably the easiest and most flexible way to do that is to bring out I2C and GND/5V with maybe 1 or 2 more digital signals to a 4-6 pin header next to the LCD connector.
Last edited by frob on Wed Mar 07, 2012 3:56 pm, edited 1 time in total.
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Re: Announcing the ORDuino !

Postby bdring » Wed Mar 07, 2012 3:13 pm

Why do the motor connectors appear to have 8 connections? Is the micro step mode set by channel or do all channels need to be set together?
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Motor connections and config

Postby frob » Wed Mar 07, 2012 3:38 pm

bdring wrote:Why do the motor connectors appear to have 8 connections? Is the micro step mode set by channel or do all channels need to be set together?

I have 2 digital (endstop or alternate use) signals there, plus GND and Vmotor connections on each motor connector.
This allows you use different voltages on each motor if you prefer, by severing the connection to the on-board Vmotor bus;
- or to power / control other remote auxiliary circuitry associated to that axis;
for example, i envision a future "intelligent dual extruder" taking advantage of this.
or a simple remote (I2C) thermocouple interface + AC/DC power switch for various heaters or even remote BLDC spindle controller.

imho it also potentially keeps the wiring neater, and lets me reuse the same terminal block connector across the board to keep the BOM and parts cost lower.
the only reason i didnt use the same connector on the power and heater connections is that they're not rated to handle the 10's of amps needed there; instead i'm using a pair of similar 3-pin 5mm terminals i use in other products i'll be producing soon, there that are rated for the higher currents and can more easily take heavy gauge wire.

The micro-step mode is ganged together for the whole board, and set by dip switches and/or potentially under CPU control.
Is there ever a situation where you need to have different step modes for different axes ?
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Re: Announcing the ORDuino !

Postby Zat German » Wed Mar 07, 2012 5:58 pm

Has the Enable pin for the drivers been broken out? If not, it might be something to consider. I want to put a big red Emergency stop next to my machine to kill the steppers, hot ends and heated bed instead of just cutting power to the board and everything else at once when things go awry. Having an input to the board to tell it that an e-stop has occurred(different from limit/home switches) could also be beneficial from a software perspective.

Sorry I did not bring this up sooner, I have been pretty busy with a lot of different stuff.
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Re: Announcing the ORDuino !

Postby frob » Wed Mar 07, 2012 7:04 pm

Zat German wrote:Has the Enable pin for the drivers been broken out?

The enables are all connected together to a CPU IO pin.
I dont yet have any other connection to that.
My thinking was the E-stop should be monitored by the CPU using a different IO,preferably a top priority interrupt pin -
So the CPU will immediately know to do an instantaneous hard stop, without losing its position, so it is possible to continue after.

If you directly override the driver enables, the CPU doesn't know this and will keep stepping merrily away thinking nothing unusual happened.
Also, the motors don't necessarily stop in their tracks - being just de-enegised, they would likely keep coasting for a while, so more chance of bad stuff happening, and even if you do monitor the enable line then so the CPU knows, you will loose sync in the build and your part is unrecoverable.

So because of that i think its best to keep the CPU in the loop. Using a high-priority interrupt means even if the program crashed and the printer is going bezerk, it should be able to stop itself and prompt for what to do next, like move to a home position, or rebooting if necessary.
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