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Adjusting frequency NE556

  • Thread starter Dave, I can't do that
  • Start date
D

Dave, I can't do that

Jan 1, 1970
0
Hi,

The following is a PDF of a motor control kit...

http://www.electronickits.com/kit/complete/motor/ck1400.pdf

Currently it is designed to run at around 410Hz.

I assume that too will be the frequency for the PWM output but I need
5KHz from the PWM.

I looked at the formula for frequency on page 1 and it may as well be
written on Chinese as far as I can tell.

Could someone with a brain significantly superior to mine, please tell
me what components need to be changed to get this to operate at 5Kz. I
need this to operate at 5KHz, 5volts and 100mA PWM output from 0%-95%

Thanks so much.

Dave
 
J

Jasen Betts

Jan 1, 1970
0
Hi,

The following is a PDF of a motor control kit...

http://www.electronickits.com/kit/complete/motor/ck1400.pdf

Currently it is designed to run at around 410Hz.

I assume that too will be the frequency for the PWM output but I need
5KHz from the PWM.

R3 R4 and C2 control the rate of the PWM

as you want it to run about 12 times faster you need to decrease the
capacitor (C2) or the resistors (r3,r4) by a factor of 12.

I'd replace C2 with an 8.2nF capacitor which should get you fairly
close to 5Khz, (if a more precise 5khz is needed also replace r3 with a 27K with
a 10K trimmer in series.)

C6 and r5 are also responsible for the on-time of the pulses and
one of those should also be adjusted down by a factor of 12 (probably
easiest to change the capacitor again)

there is a different, simpler, PWM cricuit (that works well especially
if precise control or stability of the frequency is not needed) that
uses just a single 555 (or half of a 555) and places the variable
resitance with a pair of steering diodes inside the oscillator circuit.

Bye.
Jasen
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
f=1/.693*c (r1+2*r2)there is also calculation for t1+t2=f I have no idea what you need.
 
D

Dave, I can't do that

Jan 1, 1970
0
Thanks Jasen and Jerry, I will give them a try.

Dave
 
J

Jamie

Jan 1, 1970
0
Jasen said:
R3 R4 and C2 control the rate of the PWM

as you want it to run about 12 times faster you need to decrease the
capacitor (C2) or the resistors (r3,r4) by a factor of 12.

I'd replace C2 with an 8.2nF capacitor which should get you fairly
close to 5Khz, (if a more precise 5khz is needed also replace r3 with a 27K with
a 10K trimmer in series.)

C6 and r5 are also responsible for the on-time of the pulses and
one of those should also be adjusted down by a factor of 12 (probably
easiest to change the capacitor again)

there is a different, simpler, PWM cricuit (that works well especially
if precise control or stability of the frequency is not needed) that
uses just a single 555 (or half of a 555) and places the variable
resitance with a pair of steering diodes inside the oscillator circuit.

Bye.
Jasen
And then again, you can use a dual comparator/op-amp, one unit as the
triangle wave generator while the other is used as the comparator.
With the above, you can obtain 0..100% PWM at what ever the triangle
wave is set for with out screwing with duty cycle factors.

http://webpages.charter.net/jamie_5"
 
J

Jamie

Jan 1, 1970
0
Jamie said:
And then again, you can use a dual comparator/op-amp, one unit as the
triangle wave generator while the other is used as the comparator.
With the above, you can obtain 0..100% PWM at what ever the triangle
wave is set for with out screwing with duty cycle factors.

http://webpages.charter.net/jamie_5"
And to add to my post since JF got so sentimental about it.

http://www.4qdtec.com/pwmmod.html

The above can be replaced with a comparator or
op-amp that employs the totem pole outputs. Meaning,
they source and sink on the output. This can eliminate
the need for the high side R that is being used now since
the LM339 id open collector on the outputs.

Personally, I would use a LM358 or something in that line
which is what I normally use..

Many others will work of course, that is just an example.

And John, I don't have time to translate schematics to ASCII
art because I would have to do so by hand.




http://webpages.charter.net/jamie_5"
 
P

Paul E. Schoen

Jan 1, 1970
0
Dave said:
Hi,

The following is a PDF of a motor control kit...

http://www.electronickits.com/kit/complete/motor/ck1400.pdf

Currently it is designed to run at around 410Hz.

I assume that too will be the frequency for the PWM output but I need
5KHz from the PWM.

I looked at the formula for frequency on page 1 and it may as well be
written on Chinese as far as I can tell.

Could someone with a brain significantly superior to mine, please tell
me what components need to be changed to get this to operate at 5Kz. I
need this to operate at 5KHz, 5volts and 100mA PWM output from 0%-95%

Thanks so much.

This would be very easy to implement with a PIC, but then you would need to
learn how to program using PIC code, which is not all that simple.
Microchip has an app note for motor control using a PIC16F684, which I have
used for a step-up DC-DC boost converter. The document shows the schematic
and basic operation of a motor control kit which I got as a prize at a
Microchip seminar. You can have a look at:
http://ww1.microchip.com/downloads/en/AppNotes/00893a.pdf

Another good app note is:
http://ww1.microchip.com/downloads/en/AppNotes/00905a.pdf

These show a full bridge controller, which is more complex than a single
MOSFET with PWM, but it is really much better because it can reverse
direction under software control, and you can also use dynamic braking
which slows the motor more quickly and provides more precise control.

If you really want good control, a stepper motor is best. The PIC16F684 is
also usable for stepper motors, and I have had some experience with that
device if you want to go that route.
http://ww1.microchip.com/downloads/en/AppNotes/00906B.pdf
http://ww1.microchip.com/downloads/en/AppNotes/00907a.pdf

But stepper motors are even more complex, and I think you want something
very simple. Still, the PIC16F684 would be able to provide a nice PWM drive
to a logic level MOSFET at 5 kHz, and you could add a pot across the 5 VDC
power supply to an A/D pin, and you could have a complete PWM circuit with
only a few components. And you could change the frequency just by
reprogramming it, or add other things like pushbuttons, LEDs, and even
literally "bells and whistles".

You can use a PICkit 1 (which I have) to build your entire motor
controller. It connects by a USB cable to your computer for programming,
and it has a prototyping card that can be snapped off and used separately.
There is also a PICkit 2 that has more features. Here's more info:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en010053

And for the PICkit 2:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en023805

I could give you a PC board that could be used to make a simple PWM motor
control using a PIC16F684 or the similar PIC16HV616 (which I am using). The
board is designed to produce up to 60 VDC at 750 mA as a boost converter,
but you could replace the inductors with a motor (and diode), and you could
add an external pot for speed control. But it's only about 1" x 2.5", and
mostly SMT. I got about 100 boards for about $150, and I could spare a few.

I also have about 100 boards that were designed for an LT1247 or UC1843a
PWM controller, and they might work also. It's a simple IC, and you could
get a free sample in DIP package from Linear Technology or TI. The boards
are essentially scrap, and I have some extra parts, so let me know if you
(or anyone else) is interested. Again, this was for a boost converter, and
it works, but not quite right.

Sorry for getting carried away, but these are just some other ideas that
might help you with your project, and maybe you might enjoy a more
software-oriented approach to circuit design with PICs.

Good luck,

Paul
 
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