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Topic: generating a -10v...+10v control signal from an arduino (Read 5300 times) previous topic - next topic

Jonnym

hi everyone,

thanks for all the pointers and ideas- it seems that the catalog page was missing a bit of info that the data sheet filled in. who would have thought it :) 

to move this thing in direction "A", apply a voltage to pin D, this voltage is ranging from 0-10v. 
to move this thing in direction "B", apply  0-10v to pin E.

pin D and pin E are to remain connected to their respective branches of the circuit. i would imagine i could break something it 10v was on pin D and pin E at the same time?

the data sheet says that if only one signal pin is available, then the other needs to be grounded. since i will be using both signal pins - there is no need to ground the pin, when traveling in the opposite direction, correct?

i'll keep reading a bit and post a circuit sketch in a bit -- again thanks for the help

_Jon




oric_dan

I agree with dc42 that his ckt should work, and all the way from 0V to 10V output, as the LM358
opAmp has input common-mode range down to ground.

The one thing that may be an issue is that 1st-order filtering of the PWM signal will leave a little
ripple on the DC-level, so the valve may jitter some. You can deal with that by using a PWM
frequency much much greater than the R*C time constant of his filter, but this will also reduce
the frequency response of the valve, if that's an issue.

Jonnym

hi oric_dan,

thanks for the reply ---  although it is bit above my knowledge level.

...filtering of the PWM
so if i look at it on a scope i'll see some stepped lines, and not super smooth, the faster the pwm frequency, the less noticeably this becomes?

...PWM frequency much much greater than the R*C time constant of his filter
??? the math of circuits has got me confused. i used to have respectable math skills, but haven't used them in many years. could you clarify a bit.

...response time of valve.
--slow is fine. :)

i'm putting together a parts order now... any suggestions?

_J

oric_dan

#18
Nov 16, 2012, 04:27 am Last Edit: Nov 16, 2012, 04:31 am by oric_dan(333) Reason: 1
This should help explain it,

http://www.google.com/search?hl=en&safe=off&q=PWM+ripple&bav=on.2,or.r_gc.r_pw.r_qf.&bpcl=38625945&biw=1153&bih=827&um=1&ie=UTF-8&tbm=isch&source=og

You can see dc42's same ckt here,

http://www.hoelscher-hi.de/hendrik/english/demux.htm

For a 1st-order RC low-pass filter, the 3dB or 'cutoff' frequency is given by F3db = 1/(2*pi*R*C). You want the
PWM frequency to be maybe 5X this value to get reasonably small ripple. Probably better to directly access
the Arduino PWM subsystem than to use the analogWrite() function, which I believe has a fairly low frequency.

BTW, I find I'm using google images for almost everything now, in preference to a regular google search. Easier
to zero in on the perfect website, :-).

Jonnym

hi guys,

i am plugging numbers into this calculator... could you verify some of my assumption??

http://sim.okawa-denshi.jp/en/PWMtool.php

fPWM= 480 (this is the operating freq of the pwm timer? )

duty step -- the output i want. 50% if i wanted around  5v output, based on switching  0-10v

R and C values??  I got a 'pretty' curve at R =5k and C =10u. Could i expect to get better??

what is the fc - cut off frequecy term mean?

thanks
jon


Docedison

It means the frequency at which the referenced level is reduced or increased (for a high pass filter) by 3 Db or a power factor of 2.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

oric_dan

That site is very useful. The result with those numbers is not very good, so needing something more like
Fpwm=10Khz, Fc=100Hz, or 100:1 to get low ripple.

5K and 10uF -> F3db = 3.18 Hz, which is quite low, but probably ok if all you're doing is changing slowly.

dc42


That site is very useful. The result with those numbers is not very good, so needing something more like
Fpwm=10Khz, Fc=100Hz, or 100:1 to get low ripple.

5K and 10uF -> F3db = 3.18 Hz, which is quite low, but probably ok if all you're doing is changing slowly.


My suggestion was 100K and 1uF, giving F3db = 1.59Hz and time constant = 100ms. I guess we need to know how fast the OP needs to move the valve.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

oric_dan

Why aren't you asleep? It's 5:30 AM in the UK!

justjed


Quote
anyone got a better grasp of technical german??

No but if you scroll down the data sheet the bottom half is repeated in English!  ;)


You could've really impressed us all by omitting that, and just posting the English part with a 'here you go!'  ]:)
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

Grumpy_Mike

Quote
Why aren't you asleep? It's 5:30 AM in the UK!

Yes that is what I would like to know as well but for me this time.

Quote
You could've really impressed us all by omitting that

Yes though of that but opted for honesty, so never make a politician will I?

Jonnym

Hi Guys,

Me again...

I'm confused at where the RC filter would be connected in the circuit. If I was switching a transistor with one of the pwm pins, the transistor is allowing the path to ground. Is the RC filter on the collector side or the emitter side? (thinking this is an NPN)

There is a path to ground via the capacitor, is the high freq. stuff is going this route? and that's the whole point...

thanks
Jon


Grumpy_Mike

No that is totally wrong.
Collector to pull up resistor to +12V.
Collector to filter resistor. Other end of resistor to capacitor to ground and also to one of the inputs of your controller.
You need two of these circuits one for each input. You also need a common ground.

Jonnym

...and base ?  is this shown correctly?

..and emitter?.. is this show correctly?

..and load?.. is this shown correctly?

cheers.

Grumpy_Mike

Quote
.and base ?  is this shown correctly?

Yes
Quote
and emitter?.. is this show correctly?

Yes
Quote
and load?.. is this shown correctly?

No.
See previous answer.

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