OpenCalc
Revised OpenCalc case rotating, separating from the PCB, and reassembling

Open hardware / GPL-3.0-or-later

OpenCalc

A graphing calculator built to be opened, programmed, and connected.

Dual-core ESP32-S3. Embedded symbolic math. Tiny Python. A 16-channel sensor header. One USB-C cable.

See the difference Build it
240 MHz320 × 240CAS12D + 4A I/O
01 / OpenCalc vs. TI-84 Evo

More open. More expandable. Less expensive to produce.

The TI-84 Evo is the polished classroom benchmark. OpenCalc takes a different position: full project access, a real embedded CAS, exposed scientific I/O, and hardware you can rebuild.

Comparison OpenCalc V5 TI-84 Evo
Processor Dual-core ESP32-S3, up to 240 MHz 156 MHz processor
Display 320 × 240 full panel 320 × 240 panel; 319 × 209 graph area
Math engine Embedded Giac/KhiCAS CAS plus numerical math Polynomial and system solvers; no general CAS
Programming Tiny Python with graphics, keys, files, audio, math, and sensor APIs Python and TI-Basic
Expansion 12 digital, 4 analog, and shared I2C on the rear header Vendor-supported classroom accessories
Project access GPL firmware, KiCad PCB, enclosure, tests, and build files Vendor-managed hardware and operating system
Price $32–51 estimated unit costProduction estimate, not a retail offer $129.99 advertised$129.99 regular price at Staples, checked Sep. 2026
Exam use Not submitted or approved for standardized exams Approved for ACT, SAT, PSAT, IB, and AP exams

Clock speed alone is not a cross-architecture performance benchmark. Evo specifications come from Texas Instruments; price from Staples.

02 / What makes it different
OpenCalc OS tour showing calculator, graphing, apps, scripting, and games
Actual 320 × 240 OpenCalc OS interface.

The math is connected to the rest of the device.

Enter a function once, then move between its graph, table, roots, derivative, integral, tangent line, and shaded area. Alpha + Graph opens the linked analysis view.

  • Symbolic and numericalExact algebra, complex values, units such as 8 m / 2 s, calculus, matrices, statistics, and solving.
  • Programming that reaches hardwareScripts can draw, read keys, save files, play game audio, and sample attached sensors.
  • Two cores with separate jobsThe UI stays responsive while queued math and system work run on the other core.
  • One cableUSB-C handles power, charging, files, firmware flashing, and the serial console.
Front and back render of the OpenCalc V5 PCB
03 / A calculator that can measure

Read a sensor. Plot it. Keep the data in L1.

The optional V5 scientific-I/O profile provides twelve 3.3 V digital channels, four 16-bit analog inputs, and I2C. Tiny Python exposes them directly:

sensor_log.py 
sensors.rate(128)
sensors.list_clear(1)

for sample in range(60):
    value = sensors.analog_read(0)
    sensors.list_append(1, value)

print(sensors.list_count(1))

Prototype note: sensor inputs are 3.3 V only. The V5 scientific-I/O and audio paths still need final-board validation.

04 / Current status

Real hardware. Honest limits.

  • The calculator, display, keypad, USB, power system, persistence, and five games run on the prototype.
  • The embedded CAS is not full desktop Xcas; Tiny Python is intentionally smaller than CPython.
  • Long CAS/script cancellation, 99 × 99 matrices, and new V5 peripherals still need extended hardware soak tests.
05 / Build it

Clone. Build. Flash.

OpenCalc targets ESP-IDF 6.0.1 and the ESP32-S3. The repository contains the firmware, V5 KiCad project, enclosure files, storage image, and host tests.

Complete guide App status Hardware guide
Terminal 
git clone https://github.com/CoryPearl/opencalc.git
cd opencalc/firmware

idf.py build
idf.py -p PORT flash
idf.py -p PORT monitor