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Can anyone help me wire up this motor driver?

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EightBySix:
Been fiddling with this for a while now. wondered if anyone could cast their eye over it to see if I'm making any obvious mistakes.

Got a motor driver chip. SN754410NE. Here's the datasheet

Built a circuit so that i could control the direction of the motor with digital signals, but I cant get it to work. Here are a couple of pics of my circuit.

First one, to show the general layout, with the power. I supply 12v to it, for the motor power, and convert it to supply 5v on another line for the chip. Like this:



Now here is a closeup of the circuit. (I forgot to replace a Vcc wire before I took the pic, so I've drawn it in manually)



The motor wires connect to the pins that I've indicated with yellow dots. The blue wires send either a high or low depending on the position of the switch. The resistors are meant to be pull downs (as far as I understand it).

The 12v input is supposed to appear at one of the motor drive pins when I enable the relevant signal with the blue wires.
I get a 0v (or rather not quite zero, but close) when I set the signal pins low, and it changes when I set it high, but only by fractions of a volt, rather than the 12v I was expecting.

I must have:

1) misunderstood the datasheet
2) got the chip the wrong way round (there is a kind of notch at the end I'm assuming is pin1. there is a circle at the other end,but not at the edge, and the writing reads the right way around in the orientation I took the picture)
3) fried the chip whilst messing about getting it to work. Do these things tend to fry easilly? Would the responses I've seen be typical of a dead chip?

I know it's a bit of a longshot, expecting people to figure out my breadboard with just a pic, but if you dont ask...

DaOld Man:
The device on the left: Is it an inverter chip?
The datasheet (page 6/7 on the link you posted) shows inverters being used so that a + at inverter input supplies a - at pin 2 and a + at pin 7.
If this is the case, I dont see a ground supplying the inverter chip. It needs a + and - supply.
Also it is a good idea to tie all unused inputs on the inverter chip to ground so that the outputs dont fluctuate.
If that device is not an inverter, what is it?

Edit: you can test the inverter theory by attaching pin 2 to ground and pin 7 to +5vdc and see if you get anything out on pins 3 and 6. If you do, reverse pins 2 and 7 and polarity on 3 and 6 should change.

Mysterioii:
Yeah, what DaOld Man said.   :lol  Also if you have time to actually sketch out a schematic (with part numbers) it makes it easier to debug than a somewhat blurry breadboard pic, at least for me...   ;D

EightBySix:

--- Quote from: DaOld Man on May 04, 2012, 08:16:29 am ---The device on the left: Is it an inverter chip?

--- End quote ---

sorry - hard to tell from the picture. It's just a switch, like this one

the idea was to make it easy to test - with the switch one way I supply 5v to pin 2 and ground to pin 7, or vice versa switched the other way.

I tried 'hardwiring' those pins to ground/5v but still didnt see the outputs I expected.

I'll try to get a schematic, but I'm likely to make an error transcribing it  :o

DaOld Man:
Ah yes, I see the resistors to ground now. This should work. Not sure why it's not.
Your wiring diagram might shed some light.

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