May 30, 2008

Should we avoid port splitters?

When I was on Amazon.com this morning, this popped up. Could someone refresh our collective memory about why using these is not a great idea (even if the idea of more ports is very appealing)?

11 comments:

Philo said...

These splitters can be used if you know precisely what you are doing - including having an idea of the schematics of the sensors...

- the motors can be parallelled but the encoders output will conflict and won't work.
- You may parallel any number of touch sensors. But you will have trouble knowing the one which is closed - and if one is pressed you will not see others.
- You may parallel touch sensors with one i2c sensor ("digital").
- With some restrictions you may parallel touch sensor with light or sound sensor (but you won't be able to read sound or light while the button is pressed)
- You should be able to parallel i2c sensors, but load resistors inside sensors make it difficult (you may only have one resistor load per port). Mindsensors has a trick to enable that ("Auto Detecting Parallel Architecture"), but then care must be taken because of maximum total length of cable that may make i2c link unreliable.

And finally there is the issue of limited power available from NXT (180mA shared between all ports)

Robotica said...

Thanks Philo

I can only add that using a splitter can:
- result in unclear sensor readings.
- be harmfull for the NXT internals.

So a pasive splitter(like this one) is not adviced.

Martyn

Daniel Daugherty said...

If using i2c they will work fine. As long as you can control the pull up resistors on your hardware. Or multiple analog sensors that you just need to know that one of them is triggered.

Brian Davis said...

Again, they might work fine... if you know exactly what you are doing. for instance, many of the "stock" I2C sensors out there have fixed, and identical, addresses - a problem. Second, the power consumption thing can throw people for a loop - you can't just chain more and more sensors onto the output ports (which is exactly what this sort of thing "seems" to allow), and still have normal function. As to multiple analog sensors... as Philo said, you don't know which one is triggered, and in some cases (multiple light sensors ganged together) interpreting the result gets very very tricky.

Fay Rhodes said...

In other words, if you don't know what you're doing, you risk ruining your NXT. So, give it a pass.

Anonymous said...

Hello all,

I'm not that good in electronics. I got this splitter and my idea is simply use touch sensors with different resistances. This way, with some care I can even match the values with all 6 possible combinations (3x 1 pressed, 2x 2 pressed and the all 3 pressed). Am I right?

And... has anyone opened a touch sensor, to put the resistances?

Many thanks all,
Ricardo Oliveira

Anonymous said...

It can be used for networking more than two NXT's, using Sensor Port 4.

PS: I found this on YouTube:
http://www.youtube.com/watch?v=Kg56R6XzVdA

Martina said...

These splitters can be used if he know precisely what did his doing.

Martina said...

These splitters can be used if he knopw precisely.

Martina said...

These splitters can be used if he know precisely what he are doing.a

Martina said...

I love this site These splitters can be used if he know precisely what he is doing.

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