FDC1004 vs FDC2214: Choosing the Right ProtoCentral Capacitance Sensor Breakout

Both the ProtoCentral FDC1004 and the ProtoCentral FDC2214 are 4-channel capacitance-to-digital converter breakouts built around Texas Instruments sensor ICs. They look like siblings — same maker, same Qwiic-friendly form factor, same “measure capacitance over I²C” pitch — but under the hood they measure capacitance in two fundamentally different ways. That difference decides which one is right for your project.

Two different ways to measure capacitance

FDC1004 — charge-based (ratiometric CDC)

The FDC1004 is a classic capacitance-to-digital converter. It excites a sensing electrode and measures the charge it takes to drive it, producing a reading of the electrode’s absolute capacitance to ground. You connect an electrode directly to a channel input — no external resonant components — and the chip reports its capacitance. A programmable offset (CAPDAC) subtracts a baseline of up to ~100 pF so small changes on top of a large fixed capacitance stay in range, and two active shield drivers let you direct the sensing field and cancel parasitics.

FDC2214 — LC resonant (frequency-based)

The FDC2214 is a capacitance-to-digital converter that uses resonant sensing. Each channel drives an LC tank (an inductor plus a capacitor) and measures its resonant frequency. When the capacitance at the sensing electrode changes, the resonant frequency shifts, and the FDC2214 reports that shift with 28-bit precision. Because it only listens in a narrow band around the tank’s resonance, it rejects the broadband electrical noise that charge-based front-ends pick up — which is what gives the FDC2x1x family its reputation for high resolution and excellent EMI immunity.

Theory of operation

FDC1004: ratiometric charge measurement

The FDC1004 measures capacitance the direct way — through charge. It drives the sensing electrode with a known 25 kHz excitation and, each cycle, measures the charge Q = C × V the electrode holds and converts it to a digital value. Because the excitation voltage is fixed and known, the digitized charge is proportional to the electrode’s capacitance to ground. Per TI, the working principle is based on a ratiometric measurement. A programmable offset capacitor (CAPDAC) injects an opposing charge to cancel a large fixed baseline — the maximum offset capacitance is 100 pF — so the converter’s ±15 pF full-scale range is spent resolving the small change you actually care about. Two shield drivers replay the excitation onto a guard plane, steering the sensing field and reducing EMI interference and stray capacitance to nearby conductors.

FDC2214: an LC resonator measured against a reference frequency

The FDC2214 never measures charge at all — it measures frequency. Each channel drives an external parallel LC tank into continuous oscillation. The tank’s resonant frequency is f = 1 / (2π√(L·C)), where C is the tank capacitor in parallel with whatever capacitance the sensing electrode presents. When the electrode’s capacitance changes, total C changes and the resonant frequency shifts. The device digitizes that sensor frequency as its ratio to a reference frequency (f_REF) — derived from either the internal 43.4 MHz oscillator or an external clock — producing the 28-bit reading. To recover capacitance you invert the resonance equation, C = 1 / (L·(2πf)²) — exactly what the Arduino library’s readCapacitancePf() helper does once you give it the inductor value.

With the 18 µH inductor and 33 pF capacitor ProtoCentral fits by default, each tank resonates at roughly 6.5 MHz — comfortably inside the FDC2214’s 10 kHz–10 MHz sensor frequency range — and the electrode’s capacitance rides on top of that. Two things fall out of this design. First, resolution: a small capacitance change produces a frequency shift that 28 bits resolve far more finely than a 16-bit charge converter. Second, noise immunity: because the chip only looks at the narrow band around resonance, broadband electrical noise and EMI largely average out, so readings stay clean in environments that would swamp a charge-based front-end.

Specs at a glance

Resolution and noise immunity: where the FDC2214 pulls ahead

For applications that live or die on tiny, clean signals — proximity, gesture, fine displacement, material analysis — the FDC2214’s resonant method is the stronger tool. Its 28-bit conversion resolves capacitance changes far smaller than a coarser 16-bit converter can, and its narrow-band measurement ignores the broadband interference that would otherwise swamp those small changes. In a noisy lab or an enclosure full of switching electronics, that EMI immunity is often the deciding factor: you get a usable signal where a charge-based sensor would need careful shielding and filtering to come close.

The FDC2214 also reaches further. Because you size the LC tank for your application, you can trade range against sensitivity and sense through thicker non-conductive materials than a directly-coupled electrode comfortably allows.

When the FDC1004 is the right choice

• You need absolute capacitance. The FDC1004 reports capacitance to ground directly — no inductor value to characterize, no resonance to convert.
• Liquid-level and fluid sensing. Single-ended measurement against ground is a natural fit for level probes and tank gauging.
• Simplicity matters. Attach an electrode and read — no LC tank to design or populate.
• You want shield drivers and offset built in. The CAPDAC and active shields make ground-referenced electrode designs straightforward.

When the FDC2214 is the right choice

• Proximity and gesture sensing. High resolution plus EMI immunity makes for responsive, stable touch-at-a-distance.
• Material and thickness analysis. Small permittivity changes show up clearly in the resonant frequency.
• Noisy environments. The narrow-band resonant method rejects interference that degrades charge-based readings.
• You need the finest resolution. 28 bits resolves changes a 16-bit converter simply can’t see.

Board differences worth knowing

ProtoCentral’s FDC2214 breakout ships with a default LC tank — an 18 µH inductor and a 33 pF capacitor — populated on all four channels, so every channel resonates in a useful range out of the box; you just add an electrode. You can retune any channel by swapping components, in practice usually just the inductor. The FDC1004 breakout needs no resonant components at all — its strengths are the on-chip shield drivers and CAPDAC offset that make single-ended electrode designs easy. Both expose I²C on Qwiic connectors (3.3 V) and 0.1″ headers, which can also be powered at up to 5 V.

Quick recommendation

If you’re measuring how much capacitance is present — a liquid level, an absolute value to ground — reach for the FDC1004. If you’re measuring tiny changes with the highest resolution and the best noise immunity — proximity, gesture, materials — reach for the FDC2214. Many benches end up with both, because they answer different questions.

Get started

• ProtoCentral FDC2214 breakout — and its Getting Started guide
• ProtoCentral FDC1004 breakout
• Datasheets: TI FDC2214 · TI FDC1004