The physical plumbing is finally coming together! I received the necessary Tee-connectors and an analog manometer, which allowed me to successfully plumb the pressure transducer into the hydraulic system.

Here is what the test bench looks like right now:

With the hardware in place, it was time to validate the software.

1. Linearizing the Pump (The LUT)

Vibratory pumps are notoriously non-linear. To make the PID controller's life easier, I previously built a Look-Up Table (LUT) to map the AC phase delay to actual expected pump output. I ran a quick manual power-output sweep to verify this, and the results are excellent. The LUT successfully forces the vibratory pump to behave linearly across its pressure range!

2. Taming the Pressure (PID Control)

With the pump behaving linearly, I closed the loop. After running some experiments with the p_kp and p_ki coefficients, I successfully brought the system under control. The machine can now rapidly hit and hold a target pressure without oscillating. (Note: Ignore the temperature line in the graph below—the NTC sensor is currently disconnected while I focus on hydraulics!)

3. The "Shot Saver" (Dynamic Flow Limiting)

One of the coolest software features I’ve implemented is a dynamic flow limit. In standard espresso, if your coffee puck cracks (channeling), the physical resistance disappears, the flow rate spikes, and the shot is ruined.

I tested my safety clamp: I set a hard maximum flow limit in the active profile. As you can see in the telemetry, the exact moment the flow hits the limit, the system aggressively drops the pressure to clamp the flow rate, effectively "saving" the shot!

4. Hardware Quirks: The 3ms DAC and a Phase Mystery

While scrutinizing the high-speed telemetry on the oscilloscope, I noticed two fascinating quirks about the hardware.

First, despite the pressure transducer having an "analog" voltage output, looking closely at the signal reveals a distinct digital stepping nature. It looks exactly like an internal DAC updating its output buffer every 3ms. It is fast enough for PID loop, but an interesting reminder of how modern "analog" sensors actually work internally.

Second, I found a mystery: When plotting the pump's Triac trigger pulse against the pressure wave, I noticed that the absolute peak of the pressure wave happens right before the Triac trigger pulse fires. 

At first glance, this seems impossible—how can the peak pressure arrive before the electrical signal that turns the pump on?

I have my theories, but I want to hear from the community. Drop a comment below with your ideas on why this electromechanical phase-lag happens!