I did some progress so far, and will log my activities and my plans in this thread so that if someone spots a mistake I'm doing, I can be warned before I do it.
First of all, I want to be as close as possible to the original design. I am not electrical or electronics engineer, and I want to take as little risks as possible. I learned electronics in college , and used to be electronics technician, but that was in my previous life… long time ago... Let's say I know the basics, and luckily, have the required tools.
So, about the project with the Rambo, I read the schematics, to make sure I am not loosing time, and I won't find I miss one pin in the end.
What I saw is :
ABOUT STEPPER DRIVERS :
There are 3 stepper driver extensions. I will only use the first 2 of them. They will interface with stepper drivers using 3 signals : Direction, Step, and Enable. That means that the current regulation has to be manually done on the stepper driver, and that the microstep value has to be hard coded. Most stepper driver modules that we can find on the shelves have embedded manual current regulation tuning potentiometer.
[img]http://www.hobbyist.co.nz/sites/default ... oller3.jpg[/img]
I just need to add microstep value selection with jumpers on 2 signals per driver. Not too difficult.
ABOUT THERMISTOR INPUTS :
There are 4 thermistor inputs on-board. One is for the bed, so I just need to add one more. I will copy the design of the existing thermistors, and interface it to a signal on the ANALOG Extension connector. On that connector I already strapped Thermistor3 to signal PK0 in order to make sure I can use this one. It works well, I can read temp on PK0, so PK0 will be used for Thermistor 4.
[img]http://s2.postimg.org/m53miphux/pk0.png[/img]
[img]http://s3.postimg.org/qu95qsbkz/therm0.png[/img]
ABOUT HOT-END HEATERS :
If you look at the schematic, FAN0 driver is made exactly the same as HEAT0, HEAT1 and HEAT_BED drivers.[img]http://s27.postimg.org/smnhg4oub/fan0.png[/img]
I will re-use it for HEAT2, and instead, use FAN1 and FAN2 for fans. They have a different design, and cannot be used to heat up a hot end. That means that I keep 2 fan drivers, one of them being FAN2 instead of FAN0, and I just need to add one more heater driver.
So, the last heater just needs a pwm output, and I will re-use the design of the Rambo to add a heater resistor driver on it.
Best option seems to be either PE3 on the PWM extension connector, or PL3 on the SPI connector because they are both unused signals. SPI connector is used by the LCD, so it will be PE3.
WHAT NEEDS TO BE DONE :
- I will make a board that will connect to ANALOG Extension, PWM Extension, and STEPPERS Extension, a bit alike the LCD board.That board will host connectors to plug in the steppers, heater and thermistor. That board will also host 2 "on the shelf" stepper drivers, and the exact copy of the Rambo design for adding one Thermistor Input and one heater output.
- I will modify the firmware to change FAN0 from a fan to a heater, and replace FAN0 by FAN2. For now, I just need to understand how SeeMeCNC modified the firmware code to enable FAN0 when you print, no matter what… so that I can remove that feature. I will modify it also to configure the additional hardware in pins.h. Not too hard.
- I must try to estimate whether I can use the onboard 12V, or if I must use, and regulate one more output from the PSU. Now, I have 5Amps fuses on board, but I may need to change them to 10Amps fuses. I have these in stock, it would not be a problem.
What do you guys think ? Is it crazy stupid
