This project is funded by IFAC Activity Fund (July 2025 to June 2026)

CuffnCode is a retrofitted blood pressure measurement system for teaching and research. In the long term, it aims to become an overinstrumented platform for developing and testing signal processing and control algorithms.

Retrofitted pump system

Analog Front End Design

A reproducible, low-noise analog front end for millivolt bridge sensors (e.g., MPS20N0040D, typically used for hobbyist sphygmomanometer), using AD620 instrumentation amplifier and TLC2272 level shift. This analog front end should also work for other millivolt instruments.

TINA-TI

AC simulation with TINA-TI:

Instrumentation amplifier gain:

$$ G = 1 + \frac{49.4\text{k}\Omega}{R_g} = 1 + \frac{49.4\text{k}\Omega}{470} \approx 105$$

TLC2272 offset:

$$ \frac{56 \text{k}}{47\text{k} + 56 \text{k}} \times 3.3 V \approx 1.5 V$$

MPS20N0040D

The MPS20N0040D is a millivolt-level bridge (≈50–100 mV full-scale; 4–6 kΩ)

TLC2272 (Dual, Low-Noise, Rail-To-Rail Operational Amplifier)

This will be used to offset the instrumentation amplifier, giving headroom for possible undershoot or for signal that goes both ways (positive and negative).

AD620

This is the instrumentation amplifier that is relatively cheap and widely available in Indonesian market.

Digital Controller

We will use STM32F411CE (the black pill) as our digital processor.

Safety & Notes

• The MPS20N0040D is fragile—avoid over-pressure.
• If powering from USB, beware ground noise from the host PC. A ferrite on the USB cable can help.

Next-to-Do

• 50/60 Hz notch filter (hum killer).
• PCB layouting.
• Performance evaluations.

Credits

• Instrumentation amplifier intro: https://www.youtube.com/watch?v=O0-iczIq1aU
• INA333 review with AD620 suggestion: https://blog.robertelder.org/cjmcu-333-ina-333-instrumentation-amplifier/
• A Designer’s Guide to Instrumentation Amplifiers (3rd Edition) https://www.analog.com/media/en/training-seminars/design-handbooks/designers-guide-instrument-amps-complete.pdf