Thanks for all the replies guys.
Someone mentioned I should use a DAC and I was thinking of going down that road.
A low pass filter does the same thing but a true dedicated chip might be the way to go.
Those boards look like they are out of stock and I want to build my own anyway.
Will check out the PCA9685 chip though. If adafruit use them it might be the way to go.
"6 address select pins so you can stack up to 62 of these on a single i2c bus, a total of 992 outputs"
Looks like the way to go as I need about 80 outputs.
@Grumpy_Mike I am driving into an op amp ... so no real load as such.
I just need the output to the op amp to slew from 0 to about 2v or 3v. I can make adjustments on the op amp circuit to suit.
As for ripple. Not much is the best answer I can give.
I appreciate there is ripple on every output but as little as possible.
Slew rate or voltage output change is not THAT important as the device I am driving is not that fast anyway .. anything less than 1ms would be fine for this job.
I have not even had a chance yet to drive the one op amp with PWM and the R/C filter so don't quite know yet so will have to have a look on my scope.
All I really DO know is that I want a lot of analog voltages coming out of the arduino into op amps.
Each op amp drives a transistor in constant current mode using negative feedback.
Thanks for all the tips so far.
Looks like putting it down a serial line and letting some other chip take care of business might be the way to go.
Will look at that Adafruit chip ... looks like it might be the one for the job.
Will let you know how I go.