This sketch is a simple tech demo of TI-Nspire CX (and, by extension, TI-84 Plus CE) communication to an Arduino-like board by using a USB-to-UART breakout with simple code that simulating the single necessary command to make the calculator think a TI-Innovator Hub is attached. This demo can control the state of a LED and read sensor data from an Adafruit BMP085 or BMP180 breakout. Serial communications through the breakout must take place at 115200 baud, since TI-Nspire OS hardcodes this speed. Disconnect the USB-to-UART breakout when programming your board.
There's three basic hardware components necessary to get this running, aside from a suitably modern calculator (TI-Nspire CX or CX II with OS 4.3 or later, or TI-84 Plus CE):
- Arduino-like board. Some tweaking may be necessary on some boards (Leonardo, for example, exposes UART pins on Serial1 and not Serial).
- USB-to-UART breakout. See the section on USB-to-UART Chipset Support for more information on what you can use.
- BMP085 or BMP180 breakout. I use the Adafruit BMP180 breakout, which is discontinued. Modifying code to use other sensors as a data source isn't too difficult. This sketch uses the Adafruit BMP085 Unified library, which you'll need to install from the Arduino IDE Library Manager before compiling.
Chipset support varies by calculator model. The TI-Nspire CX and TI-84 Plus CE support the Silabs CP2104 chipset, as this chipset is used in the first-party TI-Innovator Hub. The TI-Nspire CX II supports the CH340G chipset in addition to those supported by the TI-Nspire CX. The TI-Nspire CX does not support the CH340. The Silabs CP2102 is expected to work on all models, and FTDI chipsets are untested. FTDI may work on the TI-Nspire CX II. Any combinations outside what is listed here is untested. If you have chipset testing results, tell me on Cemetech!
To connect this to the calculator, you need a USB On-The-Go cable or adapter. A USB-A female to female adapter will not inform the calculator that it is a USB host, and neither power nor communications occur. I'm using a USB Mini-B male to USB A female adapter I got on Amazon for a few dollars; it's a generic product from China, so it shouldn't be too hard to find. Note that whatever is available these days do not use a proper USB Mini-A connector, but instead use the commodity USB Mini-B connector with the OTG ID pin correctly grounded. This can be a problem for some appliances that have actual USB Mini-A sockets, but the calculators have combination USB Mini-AB sockets and will accept both Mini-A and Mini-B.
Connect your USB-to-UART breakout, after programming your Arduino, as follows:
- Breakout 5V to Arduino VIN
- Breakout GND to Arduino GND
- Breakout TXD to Arduino RXD (D0)
- Breakout RXD to Arduino TXD (D1)
Connect the LED to pin 5, or redefine the pin number (LED_PIN in the code). Be sure to use a decent current-limiting resistor as not much power is available over USB On-The-Go.
Attach BMP085/BMP180 like any other I2C device; SDA to A4 and SCL to A5 on the Arduino Nano. These connections vary by board. Connect VIN to Arduino VIN, and GND to Arduino GND.
A debug output is available as RXD on pin 7, TXD on pin 8. Connect RXD of a second USB-to-UART breakout to pin 8 to read the debug output. The debug output is never used to receive data, so connecting RXD is not necessary provided internal pullups are doing their job.
There are a few basic commands, sent with Send "commandname" and Get varname. Newlines are stripped from the example responses given.
ISTI: always responds withTISTEM.SET LED 0andSET LED 1: sets the state of the LED that is attached by default to D5. Returns the new LED state, fetch it withGet.GET LED: retrieves the state of the LED, returning 0 if off and 1 if on.GET BAR: retrieves air pressure from the BMP180 in millibars.GET THM: retrieves air temperature from the BMP180 in degrees Celsius.
Note that when running Get on the calculator, it returns only the most recent line sent. For example, if you run the GET LED command followed by GET BAR, then perform a Get command on the calculator, you retrieve the barometer reading. Thus, you don't need to fetch the LED state after setting it.