joakimgk / casound

Silly project to interface with a Casio calculator, over its 2.5" jack serial connection, with a microcontroller. The old idea was to be able to play sounds through a small speaker or buzzer, from games on the calculator, using the SEND function. But now that I know how to do it, I am no longer bored in school making games on the calculator :)

However! It's always interesting to figure out how stuff works, so here is a small ESP8266 (Arduino) sketch which interfaces the Casio. The calculator performs a little handshake while transmitting the actual numerical value, which the ESP has to take part in. Essentially, the calculator sends some bytes and expects a certain byte in return. To me, it was interesting to learn how to read a "stream" of bytes from serial without using UDR interrupts (as I would on ATMEL chips), and also learn how to "parse" the HEX bytes and the BCD numeric payload.

The handshake protocol is described in detail here: https://www.grindheim.net/electronics/casio-comm.pdf and a neat implementation is found here: https://github.com/nsg21/Arduino-Casio-Serial-library/blob/master/CasioSerial.cpp

Logging (over wifi)

Oh, one more thing: Since I am using the RX/TX pins to communicate with the calculator, I need some other way of logging from the ESP. I know there are tools for this kind of thing, but I simply post (using GET actually) to a small Perl script on a server I have, which appends to a txt file. The log can then be viewed by SSH-ing to that server, and doing watch -n 1 tail -n 30 log.txt

Schematic

The idea is to hook the OUTPUT (i.e. GPIO2) to a piezo buzzer. Pin 3 is always ground in all the ports. The COMM port is for connecting to the Casio, where pin 3 is sleeve (ground), pin 2 is ring (TX), and pin 1 is tip (RX). These pins are connected to the RX/TX pins on the ESP in a "crossed" manner. The FLASH port is for updating the firmware (ino sketch) on the ESP, through a USB-to-TTL converter. This converter (i.e. port FLASH) must be disconnected when using the COMM port. Hold down the PROGRAM button and reboot the ESP to enter flash mode.