Arduino and SN754410 motor driver chip

Well, there is a wiring error in the circuit graphics as commented on by EvalityRules 7/27/2012 6:20:02 PM  at the bottom of the page.

I also noticed a mislabelling of the final connection to the 9V motor power supply.  It refers to pin 9 when it should be pin 8 of the bridge IC.  The 8 amp supply you are using can produce about 2 or even 3 times the current of a 9V cell.  That is a real hazzard if there is a short or wrong connection.

I sometimes wonder how those (physical) stripboard diagrams can possibly be more helpful that a conventional (logical diag) schematic, since there is more room for error on the physical diags. Still, they seem popular on the web so what do I know...

By the way, unless your motors are fairly low power, you may need external schottky diodes as in the datasheet (you should be fine for a small model motor with low inductance, since it appears that the i.c. has internal diodes too).

For initial testing, often it may be better to use a small-sized (PP3) 9V battery if you have one handy rather than your DC supply

(then, if there is a fault, you will be current limited because of the battery internal resistance, to protect your circuit slightly while you prototype. It's not a very refined approach, but is slightly better than no protection.

Thanks for the advise. This chip is puzzling; no matter how many times I

rewire the thing, it overheats, even with a 9v battery, and after changing

the chip. Surely this is something obvious.  I will try a neater method for

a photo.

Keith

Keith

I'm not sure it applies in this case, but because the drawings are poor some others may be mistaken.

The Driver IC can either have a small dot by Pin1, or it has a u shaped identification. (one site described it as '..a bite taken out ..')

In these drawings Pin1 is top left.

For anyone unsure here is a reasonable good reference to finding Pin 1  www.nteinc.com/faqs/IC_Pin1_Chart.pdf

These IC's are only good for 1Amp and thats under ideal conditions, however they do incude back emf diodes.

I have used E14's Mosfet drivers ( IR4427PBF) but you need to add diodes.

Mark

Mark,

     What a dummy! The SN..... components are next to one another in my

parts container. I was trying to use a shift register as a motor driver, a

case of mistaken identity. When in doubt, it is best to keep looking for

the most idiotic error!  Thanks for the help.

Keith

Not exactly what I had in mind, but a cure anyway.

You can pwm one input on these as well to have control.

I have found that because one motor spins backwards, there is always some slight difference.

Using pwm, you can correct for the difference, which is a bonus.

In your software, just be aware that going from forward to reverse, will impart a huge amount of energy onto a motor, unless you allow some time for it to slow down.

Secondly ensure you have a 0.1uF capacitor across the motor connections (preferably right at the motor) to stop the radiated electrical spikes.

Good luck and have fun.

Mark