# Physical Purple Electronic Thumb ## Description ADC Input Conditioner with Divider and Buffer ## Project Details - **Owner:** muthu7417 - **Created:** 3/17/2026 - **Last Updated:** 3/18/2026 - **Visibility:** Public - **ADC Filter Network:** 1k + 100nF single-pole low-pass at ADC input - **ADC Sample and Hold Capacitance Assumption:** 10-20pF - **Input Voltage Range:** 0-6.6V recommended with current divider values - **ADC Bandwidth:** 1kHz - **Noise Characteristics:** Moderate broadband input noise expected; anti-alias filtering and buffering required - **ADC Resolution:** 12-bit - **Protection Strategy:** 1k input series resistor plus BAT54 rail clamps at the protected input node - **Chosen Buffer Op Amp:** OPA333AIDBVR - **Divider Ratio:** 0.275 - **Source Impedance:** <=10k - **Measurement Goal:** Scale an external analog input to a 3.3V ADC and buffer it to reduce loading, fluctuations, and high-frequency noise - **ADC Input Range:** 0-12V input scaled to 0-3.3V ADC - **System Architecture:** ```mermaid flowchart TD A[VIN_SENSE 0 to 12V] --> B[R3 input series resistor] B --> C[VIN_PROTECTED clamp node] C --> D[R1 R2 divider] D --> E[U1 buffer follower] E --> F[R4 C2 low pass filter] F --> G[ADC_IN 0 to 3.3V] C --> H[D1 to 3V3 clamp] C --> I[D2 to GND clamp] ``` - **ADC Target Voltage Range:** 0-3.3V - **Signal Bandwidth:** 1kHz - **Chosen Divider Resistors:** 27k / 27k (ratio 0.5, suitable for 0-6.6V into 0-3.3V ADC) - **Design Notes:** ADC front-end uses R3 1k input series protection resistor, BAT54 clamp diodes to +3V3 and GND at VIN_PROTECTED, R1/R2 divider scaled for 0-12V to about 0-3.24V, OPA333 configured as a unity-gain buffer, and R4/C2 RC filtering before ADC_IN. Divider source filter capacitor C3 reduces broadband fluctuation ahead of the buffer. Op-amp follower wiring corrected so non-inverting input senses divider midpoint and output feeds only the inverting input and RC stage. ## Key Components ### D1 — [BAT54HT1G](https://www.flux.ai/adrian95/bat54ht1g~ktm.md) - Datasheet URL: https://www.onsemi.com/pdf/datasheet/bat54ht1-d.pdf - Manufacturer Name: onsemi - Role Details: Upper clamp diode from VIN_PROTECTED to +3V3 to limit positive excursions - Role: Clamp - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: Diode - Package: SOD-323 - Manufacturer Part Number: BAT54HT1G **Pins:** - A [pin 2] - K [pin 1] ### D2 — [BAT54HT1G](https://www.flux.ai/adrian95/bat54ht1g~ktm.md) - Manufacturer Part Number: BAT54HT1G - Package: SOD-323 - Role Details: Lower clamp diode from GND to VIN_PROTECTED to limit negative excursions - Part Type: Diode - Role: Clamp - Datasheet URL: https://www.onsemi.com/pdf/datasheet/bat54ht1-d.pdf - Manufacturer Name: onsemi - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - A [pin 2] - K [pin 1] ### U1 — [OPA333AIDBVR](https://www.flux.ai/jecstronic/opa333aidbvr~7a.md) - Role: Buffer - Package: SOT-23-5 - Manufacturer Name: Texas Instruments - Datasheet URL: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fopa333 - Role Details: Rail-to-rail zero-drift op-amp configured as a voltage follower to isolate the divider from ADC sampling load - Part Type: Operational Amplifier (OP-AMP) - Manufacturer Part Number: OPA333AIDBVR **Pins:** - - [pin 4] - + [pin 3] - OUTPUT [pin 1] - V- [pin 2] - V+ [pin 5] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/muthu7417/physical-purple-electronic-thumb~ak](https://www.flux.ai/muthu7417/physical-purple-electronic-thumb~ak).* --- *Generated from [https://www.flux.ai/muthu7417/physical-purple-electronic-thumb~ak](https://www.flux.ai/muthu7417/physical-purple-electronic-thumb~ak)*