I have a PWM signal to smooth out before micro input.. I'm using a res and then a 10u electrolytic cap to ground.
Is is better to use electrolytic or a ceramic here? Is better ripple with an electrolytic a factor? I'd prefer to use a small ceramic.
Where are you getting a 10uF ceramic?
10uF 25V ceramics are commonplace. Its the 47uF 100V ones that are exotic!!
In general with analog signals ceramic are less desirable due to more leakage, less
linear, being microphonic. However for smoothing a PWM signal its probably not
critical as the output isn't a low noise signal, it does have ripple, its already a
compromise. Ripple depends on time constant of RC circuit.
For higher quality conversion of PWM to DC analog signal a multipole active opamp
filter would be used, with plastic film capacitors typically.
Thanks Mark.
Overall it sounds like overall a electrolytic is better then for this. It's just some filtering, then an op amp.
Tantalum might be best, but for smoothing it doesn't make that much difference.
IMHO <47uF electrolytic is worse than ceramic if you also look at service life.
Leo..
Higher PWM frequency will give great benefits. For a 5V, 16MHz Arduino, should be able to set up a 10-bit PWM at 15.625kHz. This will give 4.88mV step resolution in programmable voltage (when filtered). If using 1K, 10µF RC filter, the peak-peak ripple voltage will be only 8mV and the settling time (response) will be 0.02sec.
Why not skip the D/A-A/D conversion, and measure the PWM pulse width directly?
MarkT:
In general with analog signals ceramic are less desirable due to more leakage,
More leakage than an electrolytic?
db2db:
I have a PWM signal to smooth out before micro input.. I'm using a res and then a 10u electrolytic cap to ground.Is is better to use electrolytic or a ceramic here? Is better ripple with an electrolytic a factor? I'd prefer to use a small ceramic.
Use something like a 10 to 100 uF aluminum capacitor in parallel with a good quality 0.1uF ceramic capacitor (the yellow or blue kind, not a disk type).
I have a PWM signal to smooth out before micro input..
If you're not using an analog (filtered) version of this signal, then reply#7 is the best solution.
If you're generating this signal yourself, then you'll already know what the duty cycle is, therefore you'll already know what output voltage the PWM represents, so there's nothing left to do.
... except maybe give us more details.