Benoit Maag had the brilliant idea of reusing two classic Texas Instruments calculators, the TI-1200 and the TI-1250, to make new RPN calculators, by replacing the original chip with a reprogrammed electronic chip with a driver.

HHC 2018: Repurposing Old TI Calculators...

RPN-1200

Despite a limited number of 19 keys, a scientific RPN calculator was created using a TI-1200, a simple "4 operations" calculator from the 1970s.

The RPN-1200 has trigonometric and logarithmic functions, power, US <-> metric unit conversions, 4-level stack with LASTX, 10 memories (STO / RCL), FIX and SCI modes.

The RPN-1200 is based on a PIC 18F2550 chip with a MAX7219 LED driver as well as a 9V power supply.

Forum HP museum...

RPN-1250

The TI-1250, simple 24-key calculator, made it possible to create the RPN-1250 which is a programmable scientific calculator, similar to an HP-29C.

The RPN-1250 has a volatile memory of 98 program steps and 3 constant memory backup areas.

The RPN-1250 also has trigonometric and logarithmic functions, power, US <-> metric unit conversions, 4-level stack with LASTX, 20 memories (STO / RCL), FIX and SCI modes, 20 labels (LBL, GTO, GSB), 8 tests (X=0, x=y, x<>0, X<>y...).

The RPN-1250 has a PIC 18F2680 chip with a MAX7219 LED driver as well as a 9V power supply.

Forum HP museum...

Eddie's Math and Calculator Blog...