RPI on RAMBo 1.4

Sorry if someone asked this before, I couldn’t find anything. I’m printing a case to house the RAMBo 1.4 and a Raspberry Pi 3 so I can use Octoprint to control it. Is been working fine using the USB but since I wanna house them I thought it would be nice to connect like I do with my Prusa 3D printer, using the GPIO pins directly. I couldn’t find any guide. Did anybody get this done? Is it even possible with the RAMBo 1.4?

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All you need to do is connect the RX and TX pins. BUT You’ll need to figure out what voltage the RAMBo rx/tx pins are running at. You’ll probably need to step the RAMBo pins down to 3.3v for the rpi. I’ve used these in the past for connecting arduinos to rpis: https://www.sparkfun.com/products/12009 If you don’t step the voltage down you’ll fry something.

RX/TX1 isn’t enabled by default. The USB is on rx/tx0, I think… Now I have to check it.

I don’t worry too much about 5V/3.3V with UART. The 3.3V from the pi to the rambo is fine, it will be enough to register correctly. The 5V tx from the rambo to the 3.3V rx on the pi might hurt it. If you were worried that sparkfun board will work, but I think just a resistor would also be enough to dampen it enough to save any trouble. Worst case, you have ruined the pi. But I think there’s <10% chance of that. It’s just a guess though.

And don’t connect any power between them, just tx,rx,ground.

It looks like RX and TX pins for the RAMBo are exposed on the Serial Extension header

https://github.com/ultimachine/RAMBo-1.4/blob/1.4/Project%20Outputs/Schematic%20Prints_RAMBo_1.4a.PDF

Which appears to be the header right next to the endstop connectors
https://github.com/ultimachine/RAMBo-1.4/blob/1.4/Project%20Outputs/PCB%203D%20Print%20(top)_RAMBo_1.4a.PDF

rpi gpio reference https://www.raspberrypi.org/documentation/usage/gpio/

If you wanted to, you can set SERIAL_PORT_2 1 in the Configuration.h and enable the RX/TX1.

In the past I’ve also connected these with a simple voltage divider circuit just using 2 resistors.

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Thank you! I’ll try that.


Is this what you mean? If so, should I do this to both RX/TX (5V) and the ground pin from the X39?

That would probably work. The rpi operates at 3.3v so in a perfect world your R2:R1 ratio would be 2:1 to get 3.3v from 5, so if R1=10k then R2=20K.

You only need to do this from the RAMBo’s TX pin that’s connected to the rpi’s RX pin. @jeffeb3 suggested above that you should not need to step up the rpi’s TX to 5v for the RAMBo. X39’s ground pin should be fine.

https://ohmslawcalculator.com/voltage-divider-calculator

[EDIT]
To clarify, in your schematic instead of Vcc 5v you would connect to RAMBo’s TX pin (5v), and the 3v output goes to rpi’s RX pin. The RAMBo’s RX pin can be connected directly to the rpi’s TX pin

That will work. But I also think just the 10kOhm between them will work too. The resistor to ground is fine, but just limiting the current with the first 10kOhm resistor is enough to keep it from breaking. I remember seeing that a lot when connecting a 5V uart to esp8266s, which are very sensitive and are 3.3V.

That didn’t do the trick initially. I research about enabling the serial communication on the Pi and I found instructions: https://www.youtube.com/watch?v=bDLn9DJR_sE

Now, connecting the RPi TX on the Rambo RX0 and the RPi RX with the 10k Ohm on the TX0 did the trick.
I’ll leave it connected overnight hopping to see my Pi not fried in the morning.
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Thank you!

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