generating a -10v...+10v control signal from an arduino

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.

oric_dan(333):
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.

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

Grumpy_Mike:

anyone got a better grasp of technical german??

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

You could've really impressed us all by omitting that, and just posting the English part with a 'here you go!' ]:slight_smile:

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.

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?

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

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.

...and base ? is this shown correctly?

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

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

cheers.

.and base ? is this shown correctly?

Yes

and emitter?.. is this show correctly?

Yes

and load?.. is this shown correctly?

No.
See previous answer.

Max232 makes a nice negative voltage source

We have already established that a negitave voltage is not needed for this.

We have already established that a negitave voltage is not needed for this.

Ditto-ed.

However, for reference, the 7662 chip is a nice 8-pin negative-voltage generator, and has
a wider voltage range than the older 7660 chips,

i was trying to do something similar a while back

http://arduino.cc/forum/index.php/topic,76821.0.html

does this one look better??

sketch3.jpg

does this one look better?

Yes.

Why don't you use proper symbols for transistors?

.. :slight_smile:

:slight_smile: :slight_smile: :slight_smile:

alright...

next set of questions... resistor sizes.

I am using a 2N3904 transistor, which may not bethe correct thing to use, but maybe it is. i don't know for sure...

the way i understand this, R1 would be the current limiting resistor for Arduino. but i can seem to find what the current needs to be to operate the get the transistor to 'turn on' (yes, i sure there is a very technical term for this :slight_smile: )

i bet i would plug the need current and something like 5v's into Ohm's law and i would get something helpful???

here's the data sheet
http://www.fairchildsemi.com/ds/2N/2N3904.pdf

i'm going to guess 10k and 5v for ohm's law values... maybe?

thanks ya'll

If you want to guess a 1k to 2.2k would be better if you want the right one. Read these

great links...

working through the numbers, i am going to assume a 200ma collector current, which would give me something different than an HFE of 30. but i'll use 30, since this looks to be rough numbers anyways.

200/30 = 6.67ma

so there's a bit of "double it for safety margin" to make sure the base is saturated.

6.67 *2 = ~14ma

reading the unlv.edu pdf

R1 =V/Ib = (5V – 0.75V)/0.014A = ~305?

and choose the closest standard... nice.. thanks

_J