555 timer calculation

N

Nathan L,

Guest
I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at pins
2 and 6, set the output frequency of the 555 to about 6.8kHz, although this
will vary according to the speed setting."

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?

I'm wanting to use it to control fans, but at the lower speed settings the
PWM becomes audible. I need to keep the output frequency preferably above
20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.
 
"Nathan L,"
I have DSE kit ZA-9178, and quoting from the text:

I'm wanting to use it to control fans,
Click to expand...

** What sort of fans ????

Not brushless DC fans ( process or fans ) I hope.



.............. Phil
 
"Nathan L," <NoSpamthenexus@ihug.co.nz.No.Spam> wrote in message
news:cpdq7s$aou$1@lust.ihug.co.nz...
I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at
pins 2 and 6, set the output frequency of the 555 to about 6.8kHz,
although this will vary according to the speed setting."
Click to expand...
Does if the cap was 0.01uF... typo in the instructions???

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?

I'm wanting to use it to control fans, but at the lower speed settings the
PWM becomes audible. I need to keep the output frequency preferably above
20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.
Click to expand...
 
"Martin" <invalid.vk2umj@invalid.yahoo.com.au> wrote in message
news:31vf58F3d10b9U1@individual.net...
"Nathan L," <NoSpamthenexus@ihug.co.nz.No.Spam> wrote in message
news:cpdq7s$aou$1@lust.ihug.co.nz...
I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at
pins 2 and 6, set the output frequency of the 555 to about 6.8kHz,
although this will vary according to the speed setting."

Does if the cap was 0.01uF... typo in the instructions???
Click to expand...
The parts list of the kit includes a "0.1uF 63VW MKT polyester". The cap
supplied has "100nJ100" labeled on it.

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?

I'm wanting to use it to control fans, but at the lower speed settings
the PWM becomes audible. I need to keep the output frequency preferably
above 20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.
Click to expand...
 
"Phil Allison" <philallison@tpg.com.au> wrote in message
news:31vbf7F3en1csU1@individual.net...
"Nathan L,"

I have DSE kit ZA-9178, and quoting from the text:

I'm wanting to use it to control fans,


** What sort of fans ????

Not brushless DC fans ( process or fans ) I hope.
Click to expand...
The circuit has good filtering and back-EMF protection built in.
In amendment to my previous post, the 555 is run at 9.1 volts, regulated by
a zener.
 
"Nathan L,"
"Phil Allison"
I have DSE kit ZA-9178, and quoting from the text:

I'm wanting to use it to control fans,


** What sort of fans ????

Not brushless DC fans ( processor fans ) I hope.


The circuit has good filtering and back-EMF protection built in.
In amendment to my previous post, the 555 is run at 9.1 volts, regulated
by a zener.
Click to expand...

** Oh dear - he is just not listening.

A "brushless DC" fan is ***NOT** a simple DC motor - it is an
electronic device and must be driven from a voltage source.

PWM drive is not on.




........... Phil
 
"Phil Allison" <philallison@tpg.com.au> wrote in message
news:31vr4fF3h11mkU1@individual.net...
"Nathan L,"
"Phil Allison"

I have DSE kit ZA-9178, and quoting from the text:

I'm wanting to use it to control fans,


** What sort of fans ????

Not brushless DC fans ( processor fans ) I hope.


The circuit has good filtering and back-EMF protection built in.
In amendment to my previous post, the 555 is run at 9.1 volts, regulated
by a zener.


** Oh dear - he is just not listening.

A "brushless DC" fan is ***NOT** a simple DC motor - it is an
electronic device and must be driven from a voltage source.

PWM drive is not on.
Click to expand...
Why exactly? I'm seeing plenty of examples around the net doing exactly
that - so long as the frequency isn't above 30kHz?
 
"Nathan L,"
"Phil Allison" .

I have DSE kit ZA-9178, and quoting from the text:

I'm wanting to use it to control fans,


** What sort of fans ????

Not brushless DC fans ( processor fans ) I hope.


The circuit has good filtering and back-EMF protection built in.
In amendment to my previous post, the 555 is run at 9.1 volts, regulated
by a zener.


** Oh dear - he is just not listening.

A "brushless DC" fan is ***NOT** a simple DC motor - it is an
electronic device and must be driven from a voltage source.

PWM drive is not on.


Why exactly? I'm seeing plenty of examples around the net doing exactly
that - so long as the frequency isn't above 30kHz?
Click to expand...

** It is certainly not the recommended nor accepted method - it may just
work
with some brushless fans but not all.

BTW

You are using the wrong PWM topology - see the back pages of any DSE
catalogue
( p 290 of the 2002/3 cat ) for the proper ( ie constant frequency) way to
get PWM drive from a 555 IC.




............. Phil
 
On Sat, 11 Dec 2004 16:40:50 +1300, "Nathan L,"
<NoSpamthenexus@ihug.co.nz.No.Spam> put finger to keyboard and
composed:

I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at pins
2 and 6, set the output frequency of the 555 to about 6.8kHz, although this
will vary according to the speed setting."

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.
Click to expand...
You're right. That must be a typo.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?
Click to expand...
The 555 has an internal 3-stage potential divider. AFAICS, the
"neutral" setting of the pot is when its wiper is set to 2/3 Vcc, ie
the frequency will not be affected at this setting.

I'm wanting to use it to control fans, but at the lower speed settings the
PWM becomes audible. I need to keep the output frequency preferably above
20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.
Click to expand...
Your brushless DC fan motors use integrated Hall effect sensors/ICs
for electronic commutation. AFAICS, straight unfiltered PWM control is
not possible for this type of design unless the PWM frequency is much
lower than the fan RPM, or unless there is a smoothing capacitor
across the fan, and/or a choke in series with the fan to convert the
pulses to flat DC. The commutation ICs can typically operate from
3VDC, although the motor may stall at this speed.

See these datasheets for examples:
http://www.anpec.com.tw/products/download/pdf/APX9141a7.pdf
http://www.anpec.com.tw/products/download/pdf/APX9140a8.pdf

This picture illustrates the electronic commutation principle:
http://www.ece.msstate.edu/~hagler/May2001/02/FIG2.JPG


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
 
Try typing '555 timer calculator' into your favourite search engine.....

Richard.


"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:p8rrr0po74a3hj2jic74qcjfo5gvkqsle1@4ax.com...
On Sat, 11 Dec 2004 16:40:50 +1300, "Nathan L,"
NoSpamthenexus@ihug.co.nz.No.Spam> put finger to keyboard and
composed:

I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at
pins
2 and 6, set the output frequency of the 555 to about 6.8kHz, although
this
will vary according to the speed setting."

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.

You're right. That must be a typo.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?

The 555 has an internal 3-stage potential divider. AFAICS, the
"neutral" setting of the pot is when its wiper is set to 2/3 Vcc, ie
the frequency will not be affected at this setting.

I'm wanting to use it to control fans, but at the lower speed settings the
PWM becomes audible. I need to keep the output frequency preferably above
20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.

Your brushless DC fan motors use integrated Hall effect sensors/ICs
for electronic commutation. AFAICS, straight unfiltered PWM control is
not possible for this type of design unless the PWM frequency is much
lower than the fan RPM, or unless there is a smoothing capacitor
across the fan, and/or a choke in series with the fan to convert the
pulses to flat DC. The commutation ICs can typically operate from
3VDC, although the motor may stall at this speed.

See these datasheets for examples:
http://www.anpec.com.tw/products/download/pdf/APX9141a7.pdf
http://www.anpec.com.tw/products/download/pdf/APX9140a8.pdf

This picture illustrates the electronic commutation principle:
http://www.ece.msstate.edu/~hagler/May2001/02/FIG2.JPG


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
Click to expand...

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.806 / Virus Database: 548 - Release Date: 5/12/2004
 
"Richard" <rkabz@ellenbrook.net> wrote in message
news:newscache$k3po8i$iio$1@news.e-wire.net.au...
Try typing '555 timer calculator' into your favourite search engine.....

Richard.
Click to expand...
Hehe I did exactly that - the first one I tried gave me an incorrect figgure
:) I didn't trust these to start with -- rightly so as I still had to check
it myself.

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:p8rrr0po74a3hj2jic74qcjfo5gvkqsle1@4ax.com...
On Sat, 11 Dec 2004 16:40:50 +1300, "Nathan L,"
NoSpamthenexus@ihug.co.nz.No.Spam> put finger to keyboard and
composed:

I have DSE kit ZA-9178, and quoting from the text:
"The 10k ohm and 5.6k ohm resistors, along with the 0.1uF capacitor at
pins
2 and 6, set the output frequency of the 555 to about 6.8kHz, although
this
will vary according to the speed setting."

However, 1.44 / ( (R1+R2+R2) * C) gives me 679.2Hz.

You're right. That must be a typo.

The "speed setting" involves a 10k pot across the supply, with the wiper
connected to pin 5 of the 555. How much does that effect the frequency?
Does the center setting (5k) of the pot set the frequency to 6k8Hz?

The 555 has an internal 3-stage potential divider. AFAICS, the
"neutral" setting of the pot is when its wiper is set to 2/3 Vcc, ie
the frequency will not be affected at this setting.

I'm wanting to use it to control fans, but at the lower speed settings
the
PWM becomes audible. I need to keep the output frequency preferably
above
20kHz for the lower speed setting.

Supply is 12V (less protection diode).


Cheers in advance for any suggestions.

Your brushless DC fan motors use integrated Hall effect sensors/ICs
for electronic commutation. AFAICS, straight unfiltered PWM control is
not possible for this type of design unless the PWM frequency is much
lower than the fan RPM, or unless there is a smoothing capacitor
across the fan, and/or a choke in series with the fan to convert the
pulses to flat DC. The commutation ICs can typically operate from
3VDC, although the motor may stall at this speed.

See these datasheets for examples:
http://www.anpec.com.tw/products/download/pdf/APX9141a7.pdf
http://www.anpec.com.tw/products/download/pdf/APX9140a8.pdf

This picture illustrates the electronic commutation principle:
http://www.ece.msstate.edu/~hagler/May2001/02/FIG2.JPG


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.806 / Virus Database: 548 - Release Date: 5/12/2004
Click to expand...
 
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