So I am trying to use Arduino to control my motor.
I connect the pin 12, pin 13 on my arduino to the 1A and 1,2EN on SN754410 (Here is datasheet http://www.sparkfun.com/datasheets/IC/SN754410.pdf ).
I didn't connect 2A,2Y,3A,3Y,4A,4Y,3,4EN,VCC2,GND3,GND4
After setting 1A and 1,2EN to be high, what I can observe is:
VCC1: 12V 1A, 1,2EN : 3 ~ 6V (Keep changing,Never lower than that value) 1Y (output volate to motor): 0.66 V, should be same as Vcc! Wrong
GND1,2 = 0, All other pins have a little voltage like 1V or 2V....
Why the output voltage is so low.... what should I do? Should I just connect all pins? Or should I add some kinds of capacitor / resistor circuit?
You should connect Vcc1 to Arduino +5v (logic supply) instead of +12v, and you need to connect Vcc2 to +12v (motor supply). Also it's best to connect all the grounds, and to connect at least the unused EN inputs to ground.
the reason we use 12V for VCC is because the motor requires a 12-36V to work functionally....
any other way to fix it? like a capacitor or resistor?
there is already a capacitor at motor...
You only need to feed 12v (or whatever the motor needs) to Vcc2. Vcc1 powers the logic, not the motor.
As you have put more voltage into the logic power pin than it was designed to take you might have damaged the chip or your arduino.
I don't think so, according to the datasheet http://www.ti.com/lit/ds/symlink/sn754410.pdf Vcc1 is (unusually) rated at 36v. Although the recommended range is 4.5 to 5.5v.
If he had read the whole document, it shows how to connect the ic.