You will find a variety of devices that use TTL serial connections. This includes:
- JPEG still camera boards - examples: Adafruit 397 (shown above), Adafruit 1386 (miniature) and Adafruit 613 (waterproof)
- GPS boards - examples: Adafruit Ultimate GPS 746, Adafruit Flora GPS 1059
- Thermal printers - examples: Adafruit Tiny Printer 2751 and Adafruit nano printer 2752
- Fingerprint Sensor - example: Adafruit 751
- Serial LCD Displays - example: Adafruit 784
- Serial to PS/2 Keyboard - example: Adafruit 1136
- XBee modules - example: Adafruit 128 and many others at Adafruit
- Ultrasonic Sensors - example: Adafruit 984 and many others at Adafruit
Check the data sheet for your device. If it is a 5 volt device, you may need a level shifting chip to interface between the TTL device and the Circuit Playground Express.
If your device is 3.3 volts safe, here are the connections you will want to make:
- Connect the Circuit Playground Express TX/A7 pad to the device RX/Receive pin
- Connect the Circuit Playground Express RX/A6 pad to the device TX/Transmit pin
- Connect the Circuit Playground Express GND/Ground pad to the device GND/Ground
If the device will be powered by the Circuit Playground Express, you can connect the 3.3V pad to the 3.3 Volt input of the device. But be sure the device will not draw more than about 300 milliamps. You can draw up to 450 milliamps if you do not use the NeoPixels on the Circuit Playground Express. See this page for details.
The Adafruit TTL serial camera is a good example board (see the Fritzing diagram at the top of the page). The TTL serial connections run at 3.3 volts so hooking TX to RX, RX to TX and ground to ground makes the communications work. The camera board must be powered by 5 volts. This is taken from the Vout pad which does have 5 volts when the Circuit Playground Express board is powered from a USB connection.