Mindboards

Hello,

I want to connect a computer fan to the lego NXT, or connect the NXT to a extern chip, that has a extern power source (probably 2 batteries ^^) that is connected to a computer fan.

Is this possible?

Thanks in advance, Dryopes

Hello Dryopes

Of course you can plug a computer fan to a NXT!
I already have done that, and there is some issues to get ride off:
0 - choose a 2 or 3 wire fan, and not a 4 wire fan, with PWM command
1 - Your PC fan has to start with a voltage as low as 7V (most of good quality ones did perform, but stock/noname fans didn't start at all, or with very poor rotation... )
2 - You have to connect "Power", the Red wire of the fan with the White wire of the NXT cable (Pin 1 of the NXT Motor Port (MA0)) and "Ground", the Black wire of the fan with the Black wire of the NXT cable (Pin 2 of the NXT Motor Port (MA1))
You should be able to command the Fan as a RCX motor, it worked for me!

To go further, You can experiment to connect "PWM", the Yellow wire of the fan with the Yellow wire of the NXT, to feed the speed into the NXT, BUT i haven't done that, and if you are not confident in your skill/knowledge, don't do that (i will experiment that in near future, but don't know if the NXT can count so fast, i will see if a divider IC will be necessary...)
Hope this help
Ben

P.S. go and read this good tutorial: http://www.philohome.com/nxtcables/nxtcable.htm, for cable building, and perhaps this one: http://www.philohome.com/nxtpwr/pwr.htm for understanding of the motor port use.
You can also refer to the hardware dev kit, freely available on the lego mindstorms website.

pbenco wrote: 2 - You have to connect "Power", the Red wire of the fan with the White wire of the NXT cable (Pin 1 of the NXT Motor Port (MA0)) and "Ground", the Black wire of the fan with the Black wire of the NXT cable (Pin 2 of the NXT Motor Port (MA1))
You should be able to command the Fan as a RCX motor, it worked for me!

One caveat: fans do have some motor startup electronics inside, they don't like to be powered backwards. If you use the above setup, make sure to always use the motor in forward direction. You might also add a diode in series, but this adds some voltage drop so the fan would turn even slower.

Out of curiosity, what do you intend to do with this NXT controlled fan?

If you have a spare motor port you can use a relay such as http://www.techno-stuff.com/relay.htm or Mindsensors relay driver (which also works as a motor driver). You can also run run up to 8 standard relays through a PCF8574 board. All of these require a continuous, small current from the NXT to keep them closed.

To save the NXT batteries, you might consider using a latching relay, which stays on until you switch it off again.

There are two types. One is switched on by a positive pulse (motor forward) and switched off by a pulse of opposite polarity (motor reverse). You could operate one of these from a motor port.

The other is switched on and off by positive pulses, so you could run two from a motor port using diodes to separate the relays (motor forward selects one relay and reverse selects the other). Or you could run 8 from a PCF8574 (or similar I2C chip).

I've done this before! My brother's old graphics card died, but before he threw it out, I removed the fan. (He buy some pretty good graphics cards!) I connected it to my mindsensors RCX Motor Multiplexer for NXT (MTRMX-Nx). I powered this by taking some wires and connecting them to my NXT's rechargeable battery. Something to keep in mind is that the MTRMX-Nx consumes about a third of the voltage that it receives, and distributes whatever remains. Input 9V, output 6V, input 6V, output 4V. So make sure you provide about 1.5 times the required voltage for your project if you use this method.