74hc138n

[hobo_UL]

hi, i'm working on a motion tracking project for college. I want to control (digital on/off) 64 motors using an UNO. I was recommended to use the 74hc138 along with 8#  74hc273's. to send 8 x  8bit messages to set the HIGH and LOW state to each of the 8 motors in each of the 8 rows.

I'm looking for some example code to introduce me to these chips. I have scoured the web and although there is mention of these chips there are no examples / tutorials for me to try.

[Magician]

This should help you  start:
http://tronixstuff.wordpress.com/2010/07/16/part-review-nxp-74hc238-decoderdemultiplexer/

[graynomad]

For 64 motors you will need 8 273s, 1 238 and 12 digital pins on the Arduino.

OTOH if you use shift registers you need 8 595s (or equivalent) and 3 digital pins on the Arduino.

So the question is, do you need the extra speed you may get from using the first approach? As you appear to be controlling normal DC motors I would suggest you don't and therefore the shift register approach is simpler and uses less components.

Next question, what type of motors and what will drive them?

______
Rob

[Grumpy_Mike]

You can't put motors into a matrix like you do LEDs.
This is because while LEDs can be multiplexed and they look to be on all the time. This dosn't happen with motors.

[hobo_UL]

thanks for the link 'magician'

'Graynomad' im using pc cooling fan motors. i will need to be able to have any number 0-64 of the motors running at any one time.

'grumpyMike' thanks for that bit of information. I will try the LED example given by magician to get me familiar with using these chips

[CrossRoads]

Be sure to follow magician's links over to the 74HC595 so you can have multiple fans on at once.

[graynomad]

im using pc cooling fan motors

Then none of the chips we're talking about will drive them.

What's the answer to my question about whether you need parallel registers or can get by with shift registers?

______
Rob

[CrossRoads]

The chips won't drive them but they can control inexpensive relays that can drive them.
Shift register chips like TPIC6B595 would be better for relays, give more options for controlling relays - 5V, 12V. different coil currents.
I have a board that can be populated with up to 12 chips, can control 96 relays. There's a picture at my signature link. Bare boards are availalble for purchase if you're interested, or one can be built up for you.

[hobo_UL]

hi.  im using tip120 transistors to switch the fans on and off. the chips will be used to trigger the tip120's.