SN754410 Circuit

Britannicus

As Always - after help !

I'm trying to set up a SN754410 IC to function as a motor driver - 2 motors forward and reverse. Reading the data sheets and the "how to" on http://www.hobbyengineering.com/appHBridge1A.html

It makes no mention "kickback diodes" - I think I've understood the wiring OK - can I just check the following jpg will not fry my BS2 STAMP ?? I've laid it out, just as I intend to wire it on strip board.

Initially I'm piggy-backing this off my BOE, so the PIN outs are "off board" but once I get this to work, will probably look to produce a board which has the STAMP in situ.

If I were to install kickback diodes, I don' t see how I could as to reverse the direction of current in my motor supply wires (green in the diagram) and therefore I couldn't reverse the direction of the motor.

Should I include some resistors between Pins and the IC or are these unnecessary ?

A further question - I read that I can use PWM to alter motor speed, is this just a question of polling the EN PIN with different Pulsout commands ?

I'd value your thoughts

A

Leon

If you look at the data sheet you will see that diodes are included on the chip. They are probably sufficient for some applications.

Britannicus

Cheers Leon - I get totally paranoid about this stuff !

PJAllen

"A further question - I read that I can use PWM to alter motor speed, is this just a question of polling the EN PIN with different Pulsout commands ?"

Perhaps PWM commands?
It's "looking for" true PWM (fixed rate, variable duty) and not the Stamp's sort, but you could give it a shot.

The Stamp probably isn't the ideal microcontroller for this IC.
A Propeller could easily be made to generate the desired PWM required, and do a lot of other stuff, too.

erco

Brittanicus & Leon: I think it's a hoot that you are both UK guys who found & helped each other on this Forum sponsored by your wayward colonies across the pond. Hope this helps to reduce the sting of that whole revolutionary war thing. Can't we all just get along?

Britannicus

Cheers Erco,

All forgotten long ago - I'm a big history buff, so I know we only fielded the "B team" on the day anyway... now if this was a French site - now that's different ! . If we held a grudge against every country where we had a war, I think by now we'd only be talking to the the inhabitants of Bhutan and Lichtenstein !. My brother lives in near Chicago, and does his best by holding fireworks parties on the fifth of November and running a cricket team, Whilst his neighbour invites him to 4th July and his son plays in the local baseball league.

I have to give a big chear for a great colonial today - it's exactly 100 years since Rutherford (NZ) discovered the structure of the atom - Way to Go Earnie!

As an update I built the circuit and stuck it on the BOE board and fired it up with baited breath....., Absolutely nothing... 'til I realised I'd copied the pin outs the wrong way round Doh! - A quick re-jig and it works a dream. I'm getting variable speeds by using Pulsout on the EN pins instead of a straight High/ low and I'm looking forward to sticking it in a 'bot.

Don' t know why I ever bothered with continuous rotation servos !

Leon

Our two leaders have been enjoying a barbecue in the grounds of 10 Downing Street:

http://www.bbc.co.uk/news/uk-politics-13533306

PJAllen

My thoughts were (and are) that higher speeds require higher duty rate which leaves less time for all other matters (sensors, comms, etc.)

Is it that your motor is good enough at lower duty and you won't require near full on or something?

With a servo it's a matter of issuing a 1-2 msec PULSOUT and then you're left with 18msec or so for other stuff before the next PULSOUT is due.

(BTW, it's Sir Ernie, cheeky. Baron Rutherford!)