Connection between boards

Mark Mara

I am a software guy so I apologize if this is a dumb question. I would like to connect a Linux board to a prop board. I have a BeagleBone Back and a Parallax PDB available. Since both boards use 3.3 volt TTL do I need anything other than a direct connection between pins and a common ground?

Duane Degn

Mark Mara wrote: »

Since both boards use 3.3 volt TTL do I need anything other than a direct connection between pins and a common ground?

If your software is well behaved then no, you don't need anything other than a wire.

If you wanted to be on the save side, you could add a 200 ohm (or so) resistor in series between the two devices. If both devices had pins set as outputs and one device set the pin high and the other device set the pin low the I/O pins could be damaged from too much current. A 100 ohm resistor is enough to keep the Prop safe but a 200 ohm would probably be a good idea for other devices which can't handle as much current as the Prop.

If you could be sure the I/O pin on the receiving device was set as an input, then just a wire is all you need.

Mark Mara

Thanks Duane, I will add resistors.

Cluso99

I would use a higher value resistor just for safety until everything settles down. A 1K will limit 3v3 to 3.3mA.

FWIW Typically, and while booting, P31=SI (input to the prop) and P30=SO (output from the prop).
If you use a GPIO pin from the BBB to the prop to reset it, a series resistor might be advisable, and perhaps a 10K pullup close to the prop on it's RST pin.
Alternately you could use the transistor reset circuit as used on the PropPlug.
This will allow you to download code to the prop from the BBB. Obviously you will require the right software on the BBB.