Tiny Code Reader CircuitPython Example

How to access Useful Sensor's Tiny Code Reader from CircuitPython.

Introduction

The Tiny Code Reader is a small hardware module that's intended to make it easy to scan QR codes. It has an image sensor and a microcontroller with pretrained software and outputs information from any identified codes over I2C.

There's a detailed developer guide available, but this project has sample code that shows you specifically how to get the module up and running using CircuitPython on a Trinkey, and output any recognized code as text to an attached computer as if the module was a keyboard.

Setting up Circuit Python

You should read the official guide to setting up CircuitPython on a Pico for the latest information, but here is a summary:

• Download CircuitPython for the for your board from circuitpython.org. For example the Pico version is available at https://circuitpython.org/board/raspberry_pi_pico/. This project has been tested using the 8.2.0 version.
• Hold down the bootsel button on the Pico and plug it into a USB port.
• Drag the CircuitPython uf2 file onto the RPI-RP2 drive that appears.

Once you've followed those steps, you should see a new CIRCUITPY drive appear. You can now drag code.py files onto that drive and the Pico should run them.

Install Libraries

The application works by emulating a keyboard and sending keypresses to the main machine to lock the screen, or minimize the main window. We need the adafruit_hid library to do the emulation, so the first step is to download a big bundle of all the CircuitPython libraries from circuitpython.org/libraries. You'll need to find the right bundle for your CircuitPython version.

Once you have that downloaded, unpack the bundle on your local machine. In the file viewer, go to the lib folder within the unpacked bundle and copy the adafruit_hid directory into the lib folder on the CIRCUITPYTHON drive. This should install the library we need to emulate a keyboard.

Wiring Information

Wiring up the device requires 4 jumpers, to connect VDD, GND, SDA and SCL. The example here uses I2C port 0, which is assigned to GPIO4 (SDA, pin 6) and GPIO5 (SCL, pin 7) in software. Power is supplied from 3V3(OUT) (pin 36), with ground attached to GND (pin 38).

The Trinkey comes with a QWIIC connector, so you should just be able to connect a QWIIC to QWIIC cable between the reader and the board's port.

Reading QR Codes

Copy the code.py file in this folder over to the CIRCUITPY drive. If you connect over minicom or a similar program to view the logs, you should see information about the codes seen by the sensor printed out, and messages about any errors encountered.

You should also be able to see the contents of any QR codes typed into your attached computer, as if the Trinkey were a keyboard. For example, if you make sure you have your cursor in a text window and then open an example QR code on your phone and hold it about fifteen centimeters or six inches from the module, facing the camera, you should see http://en.m.wikipedia.org typed in, followed by a newline. As you present other codes, those should also appear on your main machine as if they have been typed in.

Not all Unicode codes will be supported by the Adafruit keyboard library we're using, so if you do have more than just ASCII you may want to look into the alternative keyboard layouts that are available.

Troubleshooting

Power

The first thing to check is that the sensor is receiving power through the VDD and GND wires. The simplest way to test this is to look at the LED on the front of the module. Whenever it has power, it should be flashing blue multiple times a second. If this isn't happening then there's likely to be a wiring issue with the power connections.

Communication

If you see connection errors when running the code detection example, you may have an issue with your wiring. Connection errors often look like this:

Traceback (most recent call last):                                                    
  File "code.py", line 50, in <module>                                                
OSError: [Errno 19] No such device 

To help track down what's going wrong, you can uncomment the following lines in the script:

while True:
    print(i2c.scan())
    time.sleep(PERSON_SENSOR_DELAY)

This will display which I2C devices are available in the logs. You want to make sure that address number 12 is present, because that's the one used by the person sensor. Here's an example from a board that's working:

[12]  

You can see that 12 is shown. If it isn't present then it means the sensor isn't responding to I2C messages as it should be. The most likely cause is that there's a wiring problem, so if you hit this you should double-check that the SDA and SCL wires are going to the right pins.

Going Further

This script is designed to be a simple standalone example of reading data from the Tiny Code Reader, but you should check out the sample code in the Developer Guide to see more advanced use cases like provisioning wifi or keyboard emulation.