# Vintage Calculators

When my trusty HP-42S calculator began having troubles, I set out to find a replacement and was surprised to find that HP no longer made a comparable RPN calculator. Fortunately, a colleague gave me his retired HP-19C and HP-41CX, both of which needed only minor repairs. I soon discovered that there was an active used HP calculator market, and I casually started collecting them. I eventually found the calculator I’d always wanted, an HP-67 programmable, which I use almost daily.

## My Calculator Collection

- HP-19C Programmable Calculator
- HP-32E Scientific LED Calculator
- HP-34C Programmable LED Calculator
- HP-41CX Programmable LCD Calculator
- HP-67 Programmable LED Calculator
- HP 35s Programmable Scientific Calculator
- Sharp PC-1211 BASIC Programmable LCD Pocket Computer

## Calculator Articles

## Programmable Calculator Software

- A Matrix Multi-Tool for the HP 35s Programmable Calculator
- Curve Fitting for the HP 35s Programmable Calculator
- Low-Sensitivity Sallen-Key Filter Design with the HP-41C Programmable Calculator
- Low-Sensitivity Sallen-Key Filter Design with the HP-67 Programmable Calculator
- Op-Amp Gain and Offset Design with the HP-41C Programmable Calculator
- Op-Amp Gain and Offset Design with the HP-67 Programmable Calculator
- Op-Amp Oscillator Design with the HP-41C Programmable Calculator
- Op-Amp Oscillator Design with the HP-67 Programmable Calculator
- Resistor Network Solver for the HP-67 Programmable Calculator