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[Reply #45 on:]

your valve has minimum speed requirement (near dc control signal)

not sure if i understand this?? were you thinking that the control circuity in the valve needs to be updated at a certain minium frequency? which would mean the settling time of the RC portion needs to be somewhat fast?

how much would things change if i would change the PWM frequency that the Arduino is pushing out?

how is the pull-up resistor affecting the R/C filter, or does it? ( i would think this might be 'magic')

..and how did you come up with charge / discharge time ??

thanks
_J

[Reply #46 on:]

i was assuming that you dont need to change the valve quickly. aka no music fountain.

the existing time constant is very long. unless you loswer your pmw output below 200hz, i wouldnt worry about.

time constant is r*c. discharge tc is 10k*4.7u. chage-tc is 20k*4.7u.

[Reply #47 on:]

One thing we don't know is the input resistance of the valve (I couldn't find it on the datasheet). That's why I suggested using an op-amp. For the circuit you have sketched to give you the full range of control, the valve input resistance will need to be at least 55K, if you are using a 12V supply for the circuit, 1K for R2, and 10K for R3.