PWM FLAT DC
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 |
PWM FLAT DC
On 2006-04-11, Coyoteboy 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. 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 |
PWM FLAT DC
DC is just extremely low frequency AC...
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... 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 |
PWM FLAT DC
On Wed, 12 Apr 2006 20:43:01 +0100, "Coyoteboy"
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 :-) --- Why don't you replace the pots with digital pots driven bu your µC? -- John Fields Professional Circuit Designer |
PWM FLAT DC
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 µC? 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! Ta J |
PWM FLAT DC
On 12 Apr 2006 16:24:01 -0700, "Coyoteboy"
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 µC? 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! --- http://www.maxim-ic.com/DigitalPotentiometers.cfm -- John Fields Professional Circuit Designer |
PWM FLAT DC
On 13 Apr 2006 02:59:36 -0700, "Coyoteboy"
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. --- You're welcome. Glad to be able to help. :-) -- John Fields Professional Circuit Designer |
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