Sunday, June 24, 2018

Using Bitty Data Logger with a serial device connected to the micro:bit edge connector

I was asked how to connect a sensor which has a UART interface to a micro:bit and to collect and graph its data in Bitty Data Logger. To answer the question, I did some experimenting, got something working, using my PC as a source of serial data, typed in by me. Here's a video showing the experiment:

Video




Connecting the Device

I don't have one of the sensors I was asked about so I set about connecting my PC to the edge connector of the micro:bit instead, the idea being that I would type data into a serial terminal application like Putty. To make the connection, I used an adapter board which has USB at one end (for my PC) and 4 wires at the other acting as TX, RX, GND and 3.3V. I connected those wires to micro:bit edge connector pins 1, 0, GND and 3.3V respectively.

micro:bit code

My code had to do several things;
  1. map the serial interface to pins 1 and 0 instead of the usual USB port on the micro:bit
  2. read comma delimited strings from the serial interface
  3. convert each string into a number (I performed no validation in my prototype code btw)
  4. send the data over Bluetooth in the format that Bitty Data Logger would understand. See http://www.bittysoftware.com/tutorials/bitty_data_logger_makecode.html for more information on this.

Here's what the code I wrote ended up looking like, first in JavaScript:

let reading = ""
function transmitSensorData()  {
    let pin_shifted = pin << 14;
let ev = pin_shifted | analog_value;
control.raiseEvent(
    9030,
    ev
    )
}
bluetooth.onBluetoothConnected(() => {
    basic.showString("C")
})
bluetooth.onBluetoothDisconnected(() => {
    basic.showString("D")
})
let pin = 0
let analog_value = 0
basic.showString("OK")
serial.redirect(
SerialPin.P0,
SerialPin.P1,
BaudRate.BaudRate115200
)
basic.forever(() => {
    reading = serial.readUntil(serial.delimiters(Delimiters.Comma))
    pin = 1
    analog_value = parseInt(reading)
    basic.showNumber(analog_value)
    transmitSensorData()
})

And in fact, here's the code in full:

MakeCode Project




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