Motherboard v1.2 arrived

Last week I ordered one of the blank v1.2 motherboards from makerbot. It came today. I was not expecting it until at least tomorrow.

It looks like the surplus SD/MMC cards are fit. Some of the sheild ground pins are in a different place. The mounting holes and signal pins line up perfectly. I should be able to clean off some solder mask for the ground pins.

The first step will be to bring up the processor under AVR studio, I do not have the RS485 drivers yet. I am considering using this footprint to mount a LM317 for the 3.3 SD/mmc card voltage. This of course would break the RS485.

I am leaning twards operating the extruder via I2C. The issue is how to handle the sync clock so that the extruder controller knows when the axis motors are moving. Most likely this will involve sending the step sync clocks as clock on the I2C bus.

An alternative would be to treat the I2C bus as a Digital Read Out [ DRO ] In this form, the fixed point numbers of the cartesian axis would be sent every timer tick. This would keep the location synced in all the peripheral devices. One of these devices could be an LED or LCD for direct readout.

-julie

I updated my blog With the details and photos detailing some of the input power modifications I made.

The 3.3volt regulator I got does not match the footprint of the suggested modification. This regulator has the output on the center pin. When I wrote the above posting, I had not looked at the modifications in detail, so there is no real need to scrap the RS485.

I still have not populated this yet. I would rather use I2c coms for board to board and extension. This would free up all of port D for use with one of my existing button matrix boards.

The stepper pins eat up most of the remaining port pins. This makes it awkward to hang a LCD display onto the processor.


I got a nice shot of the power modifications, So though it would be fun to link it here. In the background above right can be seen one of the compact flash midi controllers.



My project also has a name "Rep-Rat" for rats-nest.

-julie

heh wait until you see my work of today before you claim rep-rat

you should be able to get some more I/O with a 74HC575 or similar, hang it off the SPI port if it's available. That's one of the modifications I'm planning for my reprap since I'm using SPI already to read the temperature from a MAX6675 but MISO is totally unused.

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Wooden Mendel
Teacup Firmware

I have a lot of HC595 shift registers. That is what I use on my MIDI boards. Daisy chained out for as many notes as I need. TI also makes a high current version which can directly shunt a 2 amp coil. This is a tpic6b595. Mouser was supposed to get some in this month, Now the due date is July

While at the right baud rate serial can be faster than parallel, it is much harder to program and debug without a line sniffer.

MISO is needed for the SD slot, Useful when ISP loading too. There really is not that much to choose between SPI and TWI (I2C) SPI needs one address line per device. TWI uses a internal address.

As for the '595 how do you propose using it with multiple peripherals? I have seen systems where a 74HC138 has been used so that 3 lines can handle 8 !enable lines.

By pairing the '595 with a 74HC165 one can make a bi-directional system. This is what is used to read keyboards in some pipe organ and player piano conversions.

Cost wise, a tiny25 (8 pin) cost about a dollar in quantity. Uses 2 wire for the bus, two pins for power leaving 4 pins which is plenty for setting the step/dir signals. There is even an on board ADC. Downside is it does have to be programmed with at least a bootloader and unique id. If more pins are needed the tiny26 has 16 pins. The tiny25 also has an on die ntc temperature sensor. Although I am not sure I want to run one at 200C.


The '595 might be more accessible, much lower in cost to match the timers and bidirectional I/O. If one counts the PWM and adc capability then the cost for discreet really start adding up.


I suspect there are a whole class of rep-rats out there given the nature and state of the electronics.

-julie

Edited 1 time(s). Last edit at 02/25/2010 03:07PM by sheep.

I was just envisioning plugging your LCD into a '575- the SD card has a !CS line, so you would only need one more I/O to enable the 575 and access the LCD. You could also chain a bunch of '575s and get an arbitrary number of extra I/O using only one more I/O line from your chip.

I wasn't suggesting you use them for timing-sensitive things like step/dir lines, but for slower signals like the heater, fan or stepper enable signals it would be fine.

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Wooden Mendel
Teacup Firmware