How does the feedback of this op amp works? [voltammetry]
My "knee-jerk reaction" to this circuit is "those poor, melted Op-Amps! While on closer inspection, the circuit looks (at least potentially) feasible, any delay-time between voltage changes in CE and the corresponding voltage potential change at RE would likely lead to oscillations &amp; likely catastrophic destruction of the Op Amps, IMHO.
OA2 is operating as a simple "voltage follower" or "buffer amp." Its function is to take virtually no current from RE, while "reading" it's voltage, then output the same voltage with a low impedance (high current), to feed into the resistor network for OA1's inverting input.
OA1 is functioning as a comparator, with the "feedback" from OA2 mixing with the "input" from your DAC being "compared" to your reference voltage (+1V).
On the inverting input, both DAC "input" and OA1 "feedback" pass through equal-value resistors, so the voltage detected on the inverting input should be "half-way between" the 2 values (i.e. if DAC is outputting 2V, and RE is at 0V, then 1V should be sensed, or if DAC is at 2V &amp; RE at 1V, then 1.5V sensed). Whenever OA1 senses a higher input from DAC+OA2 than Vref, its output will swing low, and whenever Vref>DAC+OA2, its output will swing high.
In theory, the voltage applied to CE should reach RE fast enough that the output of OA2 will either look like a PWM waveform, or (if OA2 has a low enough slew rate) will have lower-amplitude oscillations, "seeking" a voltage output that satisfies the equation (RE+DAC)/2=Vref.
In practice, I'd make sure to use an OA2 with a LOW slew rate, in order to reduce the likelihood of having it "hit the rails" when oscillating PWM-style &amp; potentially cause the Op Amp to "latch up" to one of its two supply rails, and cease operating correctly.
You should be fine using PWM for your DAC, just make sure to put your LPF (RC works well) before the 10k resistor that's between positions DAC &amp; OA2 inverting input on the diagram, like this:








simulate this circuit &ndash; Schematic created using CircuitLab

Ideally, you may want to connect an ADC pin from between the 1K &amp; 10K resistors, so the 'duino can detect the actual PWM voltage output it's feeding into the circuit, if this is an important parameter.