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Own Ramps design with 5v switching regulator integrated

Posted by DocRaptor 
Own Ramps design with 5v switching regulator integrated
January 01, 2020 10:05AM
Hi,
I just wanted to share my variant of the Ramps 1.4. I modded it little bit, so it is now capable of 24V. It uses a LM2575 to generate 5V. It has a jumper to select the logiclevel and some jumpers (Thermistors) to be able to be used with an arduino mega and a due. It uses IRF3708 Mosfets, so it can be used with a due or a stm32 microcontroller. And there are blade fuses instade of polyfuses. I also traced out D7, D12 and D13 because they were unused on the 1.4. For SPI for TMC2130 you can use the SPI-Header of the arduinos in the middle of the board with some long pin-headers.

Edited 3 time(s). Last edit at 01/01/2020 02:31PM by DocRaptor.
Attachments:
open | download - ramps.zip (745.6 KB)
Re: Own Ramps design with 5v switching regulator integrated
January 01, 2020 04:31PM
Hi Doc, really appreciate your work but I've seen this in the other thread as well.. Please upload pictures instead of zip files. I don't want to download everything you post, especially if it's in a zip file. I have enough files of myself to worry about winking smiley Please be considerate and keep in mind that if you make your posts user-friendly, more people will reply and give you input on your work. You can't expect others to always download your stuff, then unpack it etc. Why do you keep uploading zip files?


http://www.marinusdebeer.nl/
Re: Own Ramps design with 5v switching regulator integrated
January 01, 2020 10:27PM
Very interesting.


And well done to get the central SPI pins connected, so the DUE could also be used. You might however want to be aware that the power-on state of the DUE pins is with the internal pull-up being enabled.
So you might want to consider adding some pull-down resistors to the mosfets. I have tested with both a 4K7 and a 10K pull-down on the DUE pins (for the mosfets and pin D37), and both values work, so the mosfets are not ON while the MCU is booting, or while you are programming the firmware.


For looking at good mosfet options, you might also want to take a look at the RepRap mosfet page: [reprap.org]
And look at the internal on resistance (Rds-on), as that is the value which will determine how hot the mosfet gets. The lower the Rds-on, the better, as this will allow more AMPs can be controlled, without the mosfet getting too hot.

For some reason the IRLB3034PBF is not mentioned on the RepRap mosfet page, but the IRLB3034PBF has a very low Rds-on resistance.


When using mosfets with a max of 30V, on a 24V system, I would also recommend adding a flyback diode to each mosfet. The flyback diode does not need to be very big, so something in the range of 500mA to 1A would probably be a good idea.

This page has some more information on the flyback diode benefits: [reprap.org]

Edited 1 time(s). Last edit at 01/01/2020 10:28PM by MrAlvin.
Re: Own Ramps design with 5v switching regulator integrated
January 03, 2020 08:40AM
Thanks for the tips MrAlvin,
I added some flyback diodes for each mosfet. I intendet to use the 1N4001, but I gone with the 1N5819 because its already used on the board with the 5v circut and there a ramps derivative out there using this diode (https://www.tindie.com/products/staticboards/ramps-14-sb-premium/#) . Also the guys in the store where I buy the components sometimes have less chances to mix them up and give the wrong component-count. Also the mosfets have now 4K7 pulldown-resistor each. And I also corrected the orientation of the servor connectors to match with the original Ramps.
Attachments:
open | download - ramps.zip (758.4 KB)
open | download - RAMPS_2.pdf (137.2 KB)
Re: Own Ramps design with 5v switching regulator integrated
January 03, 2020 03:02PM
I think that the 1N5819 is a very good choice, over the 1N4001.


You might want to revisit the thickness of the PCB traces for the power to the stepper drivers.

If at all possible, you might also want to place the 100uF capacitors for each stepper driver closer to where the power is being used.

The optimal placement is, so the power first gets to the cap, and then to the stepper driver. I know that this is not how the original 1.4 shield was designed, but several details on the original RAMPS shield were not ideal, but just worked okay. And no one has been wanting to change it much since.
But since you are now taking the time to do your own design, it might be worth experimenting, or at least consider these small adjustments for improvement.

Either way, the placement of the caps as close to where the power is being used, is the recommended placement, as I recall reading once, as being highly recommended by one of the stepper driver chip makers.


You might also want to consider using separat ground traces, for stepper drivers and the logic ground traces.
I have been told, that the stepper motors/drivers send out a lot of noise on both the motor power lines and the motor ground lines. I do not know how much this affects the logic and electronics, but it seems like a simple thing to do, to make separate ground traces, and only let them all meet at (or close to) the power supply ground wire spot.


I notice that you do not use the IOref pin on the arduino, to select the voltage of the Log-PWR. I have found the IOref pin to be a very easy way to ensure the correct logic power when switching between using the shield on a Mega or a Due.



On the AUX-3 connector there is a pin that is not being used. Pin 8. If one were to supply this pin with 5V, then I have found it is very easy to get the RRD LCD displays to work well, when being operated from a Due.


For optimal use with a Due, you might also want to consider adding two pins to the Aux-5, as the SDA and SCL pins on a DUE (next to the Aref pin) are unique pins. On the Due there are two separate I2C ports.


For use with the DUE, you might also want to note, that Arduino Due pins A13-A15 are NOT analog pins (neither is A12). So it might be useful to lead A9-A11 to the analog jumpers J45-J47, so it would be easy to select useful analog pins for use with the Due.
Re: Own Ramps design with 5v switching regulator integrated
January 03, 2020 03:14PM
Oh, I just now see that the J28 solder points, are placed right on top of the Arduino Mega USB connector. That might not be an optimal placement!

In order to avoid a short, when using an original Arduino Mega, with the big USB connector socket, it will be necessary to grind down those solder points on the under side of the PCB. AND - use some kapton tape on top of the USB connector.
Well, this is my recommendation (and experience) anyway. Over the years, I have made several PCB shield designs with this 'error'. For one-off PCBs it is a quick and easy fix, but if several boards are to be made, it becomes a bit time consuming grinding down those solder points on each PCB.

Or one could simply use Mega clone boards where they use the mini or micro USB. Or use the Due board.
But for 'original' Arduino Mega boards, that big USB connector really gets in the way.

Edited 1 time(s). Last edit at 01/03/2020 03:18PM by MrAlvin.
Re: Own Ramps design with 5v switching regulator integrated
January 05, 2020 11:46AM
The solder points touching the USB port was my mistake. I corrected it as far as I could.
I wanted to put 5V on the unused aux-3 pin, but I forgot about it. Now there is 5V.
Log-PWR is now on IOref. I didn't know that it can be used for this. Thanks for the tip.
And the Jumpers for the thermistors are now able to select between A13-A15 and A9-A11 instead of just disconnecting A13-A15 and than running jumpercables.
Attachments:
open | download - ramps.zip (776.5 KB)
open | download - RAMPS_2.pdf (137.9 KB)
Re: Own Ramps design with 5v switching regulator integrated
January 05, 2020 01:01PM
In July 2019 I have added a DC-DC Step Down Buck Converter 1.5V 3V 5V 9V 12V 3A Adjustable Module
For both the Arduino Mega 2560 R3 an Ramps 1.6 too allow use of a 24volt DC Supply.

[reprap.org]

[reprap.org]

And Yes I killed the AMS1117-05 before making the mods.


Electronics Technician / Computer Programmer
Re: Own Ramps design with 5v switching regulator integrated
January 06, 2020 05:01AM
Thats why I design my ramps-version with the voltage regulator integrated to avoid they need to mod a mega (or due, this ramps should also be also usable with it) itself. I have a bunch of megas with dead AMS1117-05. The LM2575 is easy, simple and able to handle up to 40V (says the datasheet, but I used it only up to 24V).
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