true analog out

Hello everybody,

I kind of need your opinion on something.

for controlling a 0-10v ballast fluorescent lamp driver (philips) I need a true analog output which can change from 0 to 10VDC. after digging through the web I´ve found the following two possibilties and i kind of need your opinion on which one might serve best.

1: smoothing out the arduino pwm with a lowpassfilter and after that cranking it up from 5v to 10v with an opamp. 2: with a tip120 or so PWM controlling a 10V source and smoothing that out with a filter.

(3): besides that i was thinking of maybe voltage dividing a 10v suppply with an R2R ladder a uln2803 and a shiftregister. (or with a digital potmeter capable of taking a 10v load (suggestions are welcome)?) what do you think would work best. I won´t have to change the voltage often (at most once every few weeks) and most importantly I need it to live long (years) probably the system will power down every day.

the thing i kind of like about the voltage divide solution would be that i´ll only have to set the "output voltage" once and after that i won´t be using the timers for the pwm which leaves them free for other stuff.

what do you think, would that work? am i making it myself unnecessarily difficult (am i rebuilding a yet existing component?) any other idea how i could voltage divide with the arduino?

thanks in advance..

How much current do you need to supply to the 0-10volt control system. If very low (say 20ma or less)then a simple potentiometer will suffice (using say a 500ohm pot) with some slight non-linearity If reasonably low (say less than 100ma) then a simple op-amp with a potentiometer input will do If higher than 100ma then you need a regulator chip such as an LM317. These have a minimum output of around 1.5 volts but if you need to get down to zero then a couple of diodes wired in series will get rid of this Using an arduino to provide a signal such as you require with very low change requirements is an absolute waste of technology. jack

1: smoothing out the arduino pwm with a lowpassfilter and after that cranking it up from 5v to 10v with an opamp.

No do it the other way round it is much easer. Put the 5v PWM signal through a transistor to generate a 10v PWM signal and then smooth it.

at first thanks for your replies.

I haven´t been complete in the information I gave, I wont use the arduino for just dimming a lamp, most importantly I need doing that wirelessly in some way. being that with IR, or RF i don´t really know yet, maybe i´ll hook it up to an openwrt router. I haven´t really decided on this subject yet. it´s a small domotica project.

about the current i dont really know, i haven´t found the datasheet on the ballast I use for now. I know I cannot be more than 2A if i remember correctly and I believe it will allready work with very little current applied.

and what do you think about the not-using-pwm solution?

besides that i was thinking of maybe voltage dividing a 10v suppply with an R2R ladder a uln2803 and a shiftregister. (or with a digital potmeter capable of taking a 10v load (suggestions are welcome)?)

while thinking about it yesterday i really kind of like the idea of not using pwm. if I also want to use IR and maybe an additional servo or stepper motor or so I might get in trouble with my timers.

Listen to GrumpyMike - he knows all!

PWM is the way to go, if the control current is small, then you will have no problem at all smoothing it with a relatively modest capacitor. I doubt that you will need to use an op amp.

Keep it simple.