PWM > FLAT DC

C

Coyoteboy

Guest
I'm looking to use the PWM outputs from my IC to produce an analogue value
using an RC network. Unfortunately everywhere I've found in searching only
gives calculations for if i want analogue waveforms, not flat constant (as
possible) outputs. Is this going to be a trial and error thing where RC
sizes are systematically swapped or is there a known method of
approximating? I can alter my PWM frequency (and obviously duty) as needed.

Cheers
J
 
On 2006-04-11, Coyoteboy <coyoteboyuk@hotmail.com> wrote:
I'm looking to use the PWM outputs from my IC to produce an analogue value
using an RC network. Unfortunately everywhere I've found in searching only
gives calculations for if i want analogue waveforms, not flat constant (as
possible) outputs. Is this going to be a trial and error thing where RC
sizes are systematically swapped or is there a known method of
approximating? I can alter my PWM frequency (and obviously duty) as needed.
Click to expand...
DC is just extremely low frequency AC...

you won't get flat DC with an RC network. but you can get arbitrarily low
ripple. how low do you need it and what settling time can you accept when
changing levels...

Bye.
Jasen
 
DC is just extremely low frequency AC...
Click to expand...
You have a point :)

you won't get flat DC with an RC network. but you can get arbitrarily low
ripple. how low do you need it and what settling time can you accept when
changing levels...
Click to expand...
I will give you more of an idea on the work - I'm replacing the pots in a
radio control transmitter with a microprocessor so i can interface with a PC
(instead of making a custom Tx which is beyond me and more expensive). I'm
not sure on the minimum ripple (dont want the servos twitching really but
I'd hope to have approximately 100 possible throttle 'positions', the pot
will produce infinitely variable output i know but the servos dont have
infinitely variable positions IIRC. Either way it wont matter if the servos
'twitch' a tiny amount, so long as the response time isnt too slow. Response
time - somewhere <20ms. I can investigate further- unfortunately my analogue
circuit knowledge is poor (im trying to learn!) but my microprocessor side
is OK :)

Thanks for your help!
James
 
On Wed, 12 Apr 2006 20:43:01 +0100, "Coyoteboy"
<coyoteboyuk@hotmail.com> wrote:

I will give you more of an idea on the work - I'm replacing the pots in a
radio control transmitter with a microprocessor so i can interface with a PC
(instead of making a custom Tx which is beyond me and more expensive). I'm
not sure on the minimum ripple (dont want the servos twitching really but
I'd hope to have approximately 100 possible throttle 'positions', the pot
will produce infinitely variable output i know but the servos dont have
infinitely variable positions IIRC. Either way it wont matter if the servos
'twitch' a tiny amount, so long as the response time isnt too slow. Response
time - somewhere <20ms. I can investigate further- unfortunately my analogue
circuit knowledge is poor (im trying to learn!) but my microprocessor side
is OK :)
Click to expand...
---
Why don't you replace the pots with digital pots driven bu your ľC?


--
John Fields
Professional Circuit Designer
 
John Fields wrote:
On Wed, 12 Apr 2006 20:43:01 +0100, "Coyoteboy"

---
Why don't you replace the pots with digital pots driven bu your ľC?

John Fields
Professional Circuit Designer
Click to expand...
Until about 30 seconds ago i wasnt aware you could get them, and Ive
not priced them up. Or what the interface requirements are. But I will
look into it as a possibility!

Ta
J
 
On 12 Apr 2006 16:24:01 -0700, "Coyoteboy" <coyoteboyuk@hotmail.com>
wrote:

John Fields wrote:
On Wed, 12 Apr 2006 20:43:01 +0100, "Coyoteboy"

---
Why don't you replace the pots with digital pots driven bu your ľC?

John Fields
Professional Circuit Designer

Until about 30 seconds ago i wasnt aware you could get them, and Ive
not priced them up. Or what the interface requirements are. But I will
look into it as a possibility!
Click to expand...
---
http://www.maxim-ic.com/DigitalPotentiometers.cfm


--
John Fields
Professional Circuit Designer
 
http://www.maxim-ic.com/DigitalPotentiometers.cfm
--
John Fields
Professional Circuit Designer
Click to expand...

Cracknig, cheers - they look great, and i should be able to run two of
those off once uPro as well when ive figured out the input command
signals. Thanks for the link.

J
 
On 13 Apr 2006 02:59:36 -0700, "Coyoteboy" <coyoteboyuk@hotmail.com>
wrote:

http://www.maxim-ic.com/DigitalPotentiometers.cfm
--
John Fields
Professional Circuit Designer


Cracknig, cheers - they look great, and i should be able to run two of
those off once uPro as well when ive figured out the input command
signals. Thanks for the link.
Click to expand...
---
You're welcome. Glad to be able to help. :)

--
John Fields
Professional Circuit Designer
 
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