Can anyone help me wire up this motor driver?

[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.     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...   

[EightBySix]

The device on the left: Is it an inverter chip?

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 

[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.

[Mysterioii]

edit: nevermind, mis-interpreted something....   

[DaOld Man]

If you are getting correct voltages on all the pins, only other thing I see is that the datasheet 6 shows a 10K ohm resistor between pin 1 and +5VDC.
Could the enable input on this drive be sensitive to high current? Chip might be fried, but Im not sure about this, info on the data sheet doesnt mention current limit on enable, but I could have missed it.

[Mysterioii]

Really not trying to just echo everything DaOld Man says but it's turning out that way...   

Nothing really stands out to me either.  I wouldn't think that the resistor on the enables would really be critical, but they must've shown it for a reason.  I would definitely agree that you should swap out the chip if you have any spares (hope you got some spares.... I'm a big fan of having spare components on hand especially if they're on the inexpensive side).  Only other thing I can think of is that maybe the outputs need to see some sort of a load but from reading the spec sheet it really doesn't seem like that would be the case.

[EightBySix]

thanks guys - I've bought another - £2.29 posted :-)

It's not beyond the bounds of possibility I got the 5v and 12v inputs confused during my experimentation. Now I know the chip better I should be OK, and I'll put those resistors in next time.

[Mysterioii]

Mouser has that chip for $1.88, but I don't know what it would cost to ship it to ya.  In general if I'm using a component that's only a buck or two then if I just need one or two I'll order five...  

http://www.mouser.com/ProductDetail/Texas-Instruments/SN754410NE/?qs=AMJt07B76utKvnsRwAi7IVwhWyNixSPdHn7ATYAoPP4%3d

[EightBySix]

probably what the ebayer I bought it from is doing 
http://www.ebay.co.uk/itm/251042473622?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2648

I couldnt find a distributer that didn't either want me to buy 10 or more, or have a minimum order value.

[Mysterioii]

Mouser doesn't have minimum quantities but I dunno what it would cost to ship it to where you're at.

I love mouser... I order a lot of components from them.

[EightBySix]

Well, new chip arrived, and it worked! (I added the extra resistor to be safe). I noticed that it wasn't running at full speed though. Also each time I flipped my direction switch, it took longer and longer to accelerate until it wouldn't start at all, and I'm back to square one. At least this time I know my pin connections are ok and I need to look elsewhere for the problem. I know that back emf can be produced, but the chip is supposed to contain protective diodes. Some circuit diagrams contain supplemental ones too.

I'll have to do some maths about the current draw of the motor too. Th chip should be able to handle 1A.

[DaOld Man]

Thats a tough one. Most DC motor drivers regulate speed by pulsing the motor on and off.
Could the motor be drawing more than 1 amp?
i think I would put my amp meter on it at 12 volts to see how much it is drawing.
Did the chip get hot?

[DaOld Man]

Bump.

Eightbysix, any luck with this?