556 motor control schematic?

[Adam W. Kempa]

Hello,
I'm trying to construct a speed control to adjust the speed of the
motor found in a cheap discman-style CD player to a very low speed.

I've experimented with 555 timing circuits with npn transistors, but
still can't seem to slow it enough. I think my problem has something
to do with the current circuit design's inability to get the duty
cycle below 51%.

I've poked around a bit and found that one solution to this would be
to use two 555 timers (a 556), but I haven't been able to locate a
schematic online.

Any ideas? Thanks a lot in advance for any help.
ak

 

[Ian Stirling]

Hello,
I'm trying to construct a speed control to adjust the speed of the
motor found in a cheap discman-style CD player to a very low speed.

I've experimented with 555 timing circuits with npn transistors, but
still can't seem to slow it enough. I think my problem has something
to do with the current circuit design's inability to get the duty
cycle below 51%.

Attatch the motor to the other rail, if you don't need to go above
49%

 

[John Crighton]

Hello,
I'm trying to construct a speed control to adjust the speed of the
motor found in a cheap discman-style CD player to a very low speed.

I've experimented with 555 timing circuits with npn transistors, but
still can't seem to slow it enough. I think my problem has something
to do with the current circuit design's inability to get the duty
cycle below 51%.

I've poked around a bit and found that one solution to this would be
to use two 555 timers (a 556), but I haven't been able to locate a
schematic online.

Any ideas? Thanks a lot in advance for any help.
ak

Hello Adam,
have a look at this one, it will overcome your problem.
http://www.solorb.com/elect/solarcirc/pwm1/

Have a look at these also
http://www.epanorama.net/links/motorcontrol.html#dc
http://casemods.pointofnoreturn.org/pwm/circuit3.html
http://www3.telus.net/chemelec/Projects/PWM.htm

The last one by Gary, he pops up on this group and
is a nice helpfull chap.
Regards,
John Crighton
Sydney

 

[default]

Hello,
I'm trying to construct a speed control to adjust the speed of the
motor found in a cheap discman-style CD player to a very low speed.

I've experimented with 555 timing circuits with npn transistors, but
still can't seem to slow it enough. I think my problem has something
to do with the current circuit design's inability to get the duty
cycle below 51%.

I've poked around a bit and found that one solution to this would be
to use two 555 timers (a 556), but I haven't been able to locate a
schematic online.

Any ideas? Thanks a lot in advance for any help.
ak

A single 555 timer can provide very wide range duty cycle, nearly
0-100% with the NPN output (or without)

Add a pair of signal diodes to pin 7 (discharge). One anode and one
cathode go to pin 7 the other anode and cathode go to the extreme ends
of a potentiometer. (full clockwise and counter clockwise positions).
Pick a pot that will give you the frequency you want. The wiper goes
to the timing cap (and pin 2 and pin 6 - standard astable config)

The timing cap charges through one diode and discharges through the
other, the position of the pot determines the charge and discharge
times varying the duty cycle on the output.

 

[GPG]

Add a pair of signal diodes to pin 7 (discharge). One anode and one

 

[default]

I went back to my original schematics. With the + supply to pin seven
resistor low with respect to the pot value Pin 7 works. Make it high,
and it would not be full range.

I practice I had 0-100% control using a 3.3K to pin 7 and pot of 500K

I think the circuit you mean doesn't use pin seven at all.

http://www.cpemma.co.uk/555pwm.html Look right?

 

[Paul Burridge]

Hello Adam,
have a look at this one, it will overcome your problem.
http://www.solorb.com/elect/solarcirc/pwm1/

John's right, Adam. This is a clever little design that I've built and
tested myself and give it a 5-star rating. Look no further!

 

[Kevin McMurtrie]

Hello,
I'm trying to construct a speed control to adjust the speed of the
motor found in a cheap discman-style CD player to a very low speed.

I've experimented with 555 timing circuits with npn transistors, but
still can't seem to slow it enough. I think my problem has something
to do with the current circuit design's inability to get the duty
cycle below 51%.

I've poked around a bit and found that one solution to this would be
to use two 555 timers (a 556), but I haven't been able to locate a
schematic online.

Any ideas? Thanks a lot in advance for any help.
ak

One common trick is with positive feedback from the motor's current to
the motor's voltage. When the feedback is adjusted correctly, you have
a motor with a virtual impedance of zero. It will maintain a constant
speed determined by a reference voltage. This is the trick used in
inexpensive tape drive motors.


Speed control
voltage --------> Adder ----------> Motor
^ |
| |
-- current sense<-|

 

[John Woodgate]

I read in sci.electronics.design that Kevin McMurtrie
[email protected]>) about '556 motor
control schematic?', on Sun, 14 Dec 2003:

One common trick is with positive feedback from the motor's current to
the motor's voltage. When the feedback is adjusted correctly, you have
a motor with a virtual impedance of zero. It will maintain a constant
speed determined by a reference voltage. This is the trick used in
inexpensive tape drive motors.


Speed control
voltage --------> Adder ----------> Motor
^ |
| |
-- current sense<-|

Yes, it's inexpensive and it works very well, although the above block
diagram is perhaps a little misleading. I could e-mail a basic circuit
diagram if anyone is interested.

I believe the technique was patented by Philips, but the patent has
expired. BUT YOU should check that if you want to use it commercially.

 

[Luhan Monat]

I read in sci.electronics.design that Kevin McMurtrie
[email protected]>) about '556 motor
control schematic?', on Sun, 14 Dec 2003:



Yes, it's inexpensive and it works very well, although the above block
diagram is perhaps a little misleading. I could e-mail a basic circuit
diagram if anyone is interested.

I believe the technique was patented by Philips, but the patent has
expired. BUT YOU should check that if you want to use it commercially.

Hi,

What am I missing here? You can slow down the drive motor and still
play the CD - slower?

 

[John Woodgate]

I read in sci.electronics.design that Luhan Monat

What am I missing here? You can slow down the drive motor and still
play the CD - slower?

No, it's built with the speed control being a preset pot for factory
setting, and it keeps the motor at that speed for ever (well, almost).
It's for cassette recorders; I don't know that it's used for CD motors.

 

[Kevin McMurtrie]

Hi,

What am I missing here? You can slow down the drive motor and still
play the CD - slower?

I'm assuming that the motor isn't in the CD player anymore. Audio CDs
spin at the speed that maintains the proper bitrate.

 

[Luhan Monat]

I read in sci.electronics.design that Luhan Monat
about '556 motor control schematic?', on Sun, 14 Dec 2003:




No, it's built with the speed control being a preset pot for factory
setting, and it keeps the motor at that speed for ever (well, almost).
It's for cassette recorders; I don't know that it's used for CD motors.

Yo,

I just don't think the data recovery will handle 'slow' pulses from the
CD. The clock is derived from the data rate, but there is no imbedded
clock information.

That whould be my bet, anyway. Even on turntables, with no data
recovery problems, you lowered the pitch of the music when you slowed it
down.

 

[John Crighton]

I could e-mail a basic circuit
diagram if anyone is interested.

Hello John,
I am interested.
May I have a copy of the circuit diagram.
Regards,
John Crighton
Sydney

 

[Luhan Monat]

I'm assuming that the motor isn't in the CD player anymore. Audio CDs
spin at the speed that maintains the proper bitrate.

Yes, that would explain a lot! Then a 50 ohm 2 watt wirewound pot
should be an easy solution.

 

[John Woodgate]

I read in sci.electronics.design that Luhan Monat

Yo,

I just don't think the data recovery will handle 'slow' pulses from the
CD. The clock is derived from the data rate, but there is no imbedded
clock information.

I didn't mean that CD drive motors don't need speed control; I just
don't know if the circuit we are discussing is used.

That whould be my bet, anyway. Even on turntables, with no data
recovery problems, you lowered the pitch of the music when you slowed it
down.

You'll have people trying to measure the pitch error, wow and flutter of
their CD players.(;-)

Everybody knows that if you use a power lead with solid gold conductors,
the pitch will be perfect and wow and flutter will be 200 dB below
absolute zero.