Using M5Cardputer as RPN Calculator
If you haven’t come across the M5Cardputer before don’t be fooled by the header image of this post. That keyboard is usually a full qwerty setup. The M5Cardputer is an ESP32-S3-powered device with lots of hardware wrapped around it. There is Bluetooth and WiFi, a diminutive but crisp 1.14″ TFT display, a MEMS microphone, an SD card slot, USB-C and much more. It’s a heap of programmable fun and, best of all, it’s around $30. Therefore we are not surprised to see it begin to pop up for resale with custom firmware and modifications for specific use cases, like this excellent 10LC Reverse Polish Notation (RPN) calculator.
RPN is rarely seen in modern calculators but was once a more common option. If you are unfamiliar, in math using reverse Polish notation the operators follow their operands. This means that the conventionally notated “2 + 3 – 1” becomes “2 3 + 1 -“. All operations are based on a stack, and using an RPN calculator is a great way to learn about how stacks work from a practical point of view.
RPN calculators were a hallmark of Hewlett-Packard scientific calculators, and are very collectable, often fetching a few hundred dollars for a good-condition classic. While emulation in software/apps is a good way to explore RPN nothing beats the feel of some real clicky hardware.
With its Xtensa 32-bit LX7 dual-core processor, the M5Cardputer-based 10LC is pretty powerful under the hood. It’s capable of processing 100,000 iterations of a loop in around 10 seconds. The custom 10LC firmware (pre-installed) has font size and colour options as well as optional audible keyboard beeps. The 10LC also comes with custom stickers to add to the M5Cardputer, but as this is a stock M5Cardputer under the hood, if the RPN calculator isn’t ultimately the calculator for you, you’ll find many interesting projects based around this fun little handheld.