How to control the motor

Re: How to control the motor

Postby kris_mcdougall » Thu Oct 13, 2011 8:46 am

FLOPPY DRIVE DOODLE.png
FLOPPY DRIVE DOODLE.png (170.31 KiB) Viewed 14815 times


Here's a doodle of what I was trying to describe. This is actually exactly the same drive that I have. The reason that many of the pins don't act as grounds is that they are missing from the connector on the drive! So, as I was explaining, but more concise:

EDIT: Got it to work! Strangely... it's wired exactly how I had it before, I just ripped it all off and started over. I built myself a system of switches not unlike the ones Jeri showed in her video:

- My drive is wired up as a "B" drive, so I soldered pin 12 (select B) permanently to ground,

- I have a simple on/off switch from pin 16 (motor enable B) to ground to turn on the motor,

- Pin 18 (direction) is also wired to ground via an on/off switch,

- And to step, I've wired a moment switch that joins pins 8 (index pulse) and 20 (step pulse). It steps once per revolution with the switch depressed and maintains the same position when it is not.

The direction on the stepper motor seems to have a mind of its own on this drive. Sometimes it will function perfectly, other times it will stop halfway towards the center and start stepping backwards. And on another drive, it sometimes works correctly, but most of the time it will step twice in rapid succession every two revolutions. Weird.
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Re: How to control the motor

Postby guest » Fri Oct 14, 2011 9:13 pm

perhaps the switches gave a better connection
just touching a wire
can actually cause many little contacts to occur
each one sending a pulse to the controller
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Re: How to control the motor

Postby mcanulty » Fri Oct 14, 2011 9:20 pm

Sounds like your work bench may be haunted!

I agree with what guest said, those better connections are probably to thank for it. And with regards to the direction pin, are you giving it a clear signal of power or ground when you want to change direction? It sounds a little like it may be floating so that random movements of electrons in the air are causing it to change direction. That would be my first guess, but a haunting is a close second :)
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Re: How to control the motor

Postby Paleorama » Sun Sep 30, 2012 4:35 pm

mcanulty wrote:If you have trouble with the op amps, let us know, user guest has enormous op amp knowledge and will probably be able to write up helpful posts with regards to that which may result in something good that can be put up on the main site as well. Working with the floppy audio project was how I learned not to be afraid of them and to gradually get a feeling for them. They're not so scary, in fact they're designed to take the scariness out of analog electronics. Op amps are our friends! :)


Fall is here and I've been preparing another poor floppy drive for sweet audio experimentation. Right now, the heads are hooked up to a tape player in an old radio, in which I just desoldered the tape heads. The amplification is very low so I thought it might be time to hear what dear guest has to say about the op amp matters. Would a standard LM386o or TL072 be appropriate? A gain of what? 10/50/100 times? I am curious (and keen to build!)
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Re: How to control the motor

Postby guest » Sun Sep 30, 2012 11:15 pm

you will want a really low noise, and high badnwdith opamp for this. a typical design is shown here:
http://www.analog.com/static/imported-f ... 3AN106.pdf
check out figure 21. its a non-inverting amplifier with a bass-boost. the high bandwidth and low noise are required because you will need a gain of 500 or so. they show the op-37, which has a 63MHz bandwidth and 3nV noise. its a bit expensive, but not too bad. you can try other amps like the TLC071, which is 50MHz and 7nV, and half the price.
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Re: How to control the motor

Postby Paleorama » Mon Oct 01, 2012 9:31 am

Interesting, thanks a lot! of course one prefers low noise op amps when dealing with these extreme gaining powers. Does this go for both input and output signal, and another thing: is it true that there's no way to both record to the disk and play back the signal at the same time? I tried using two of the head pins for record while playing back and it resulted in the audio supposed to be recorded was fed into the amplifier (very loud)
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Re: How to control the motor

Postby guest » Mon Oct 01, 2012 1:03 pm

i dont think the heads are shielded from one another, like they are in a reel-to-reel machine, although i cant say for sure. but i would guess that it isnt possible, as there arent seperate tracks, there is only 1 data track. the record signal amplifier doesnt need to be low noise. a high output current output amplifier might be able to write directly, without transistor buffers. the TLC071 can do 100mA, so it might be able to do it.
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Re: How to control the motor

Postby Paleorama » Tue Oct 02, 2012 2:42 pm

guest wrote: a high output current output amplifier might be able to write directly, without transistor buffers. the TLC071 can do 100mA, so it might be able to do it.


Can you specify what you mean by this? I am curious. :) Write directly?
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Re: How to control the motor

Postby guest » Tue Oct 02, 2012 8:19 pm

i mean that you could connect the output of the opamp straight to the write head. the write heads are very low resistance, so they draw a lot of current. some opamps are better at sourcing a lot of current without distorting or saturating.
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Re: How to control the motor

Postby Paleorama » Wed Oct 03, 2012 7:55 am

and by write head, do you mean the wire I soldered to the ribbon cable heads or the write data port on the control pin? I am confused because if you mean the heads, then I would still get audio out from the amp playing back the from the heads...
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