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dr hydra
10-18-2011, 10:09 PM
I am starting a project that will require connecting two props together...I have been looking at the object exchange and noticed Brandon Nimon's Fast Prop-Prop Comm...Has anyone used this program...does it work good and is it safe...my concern is related to the simple ACK function...it looks like it changes the ports (output to input / input to output) on each of the propellers...If I remember correctly you can damage a microcontroller if your output ports receive input voltage...

Bobb Fwed
10-18-2011, 10:21 PM
I'm the author of that object. I'd suggest putting a resistor in between the two Propellers (probably somewhere between 100 and 1K), especially during testing. Because, yes, it could potentially damage the IO. Once the propellers are running as expected (correct pins are setup and both RX and TX propellers have the same buffer size, etc.), there shouldn't be any danger.

A note about this object though, and I feel a bit ashamed to say it, I've had problems integrating it into certain projects I've had. I think there is a bug on the TX side, but I haven't been able to find it, and haven't had the time or a need to find the source of the problem and fix it. That being said, I know there are people on the forums that do use the object, and I have a couple projects that use it just fine.

Mike Green
10-18-2011, 10:25 PM
You can protect the I/O pins by including a 100 Ohm resistor in the connection between the two Props. That will limit the fault current to about 30 mA, well below what a Propeller I/O pin can tolerate

prof_braino
10-19-2011, 02:48 PM
I'm the author of that object. ...A note about this object though, and I feel a bit ashamed to say it, I've had problems integrating it into certain projects I've had. I think there is a bug on the TX side, but I haven't been able to find it....

Not to hijack the thread, but if you find problems due to the mentioned bug, there is another working alternative.

The propforth multiprop code (MCS) provides continuous communications channel(s) between props. It includes the protocol and data transfer is just about as fast as the prop is physically capable as fara as I know. The main intent is to allow tranparent adding prop to give the application more ccog and pin resources. It has not exhibited any issues, so we think its pretty solid. Its coded on forth, so its pretty easy.

dr hydra
02-03-2012, 07:58 PM
@mike green...I am just getting back to my project...you talked about using 100 ohms resistors for protection on the I/Os...Would a 1N4001 diode on the output work...or provide additional protection?

pedward
02-03-2012, 08:04 PM
The protection is to prevent excessive current draw. A diode wouldn't really help you, since the output pin is push-pull. If one prop drives an output low at the same time as the other drives high, you need to have some place for that to dissipate, and that's the resistor.

dr hydra
02-04-2012, 01:30 AM
so to be 100% clear...two propellers connected by 100 ohms resistor...should be perfectly safe...both I/O pins should be okay...I ask this because I will probably make a few mistakes while working on my project :)

Circuitsoft
02-04-2012, 01:47 AM
100 ohms to anywhere from 0-4v should be fine.