Connecting To TouchDRO Scale Adapter

TouchDRO application supports BlueTooth and USB connectivity for the scale adapters. Presently, the premade scale adapters use BlueTooth Classic connectivity, while a DIY adapter can be built with either a BlueTooth transceiver or a compatible USB adapter.

User Interface Overview

The "Connect" button icon is located in the upper right corner of the screen. Depending on the selected connection type, it will show either the BlueTooth symbol or the USB symbol.

Fig. 1: Connection Button
Fig. 1: Connection Button

Connection type can be chosen on the main TouchDRO setting screen by toggling the "Use USB Connection" setting. The default state is "off", which means that the application will use BlueTooth.

Fig. 2: Connection Type Button
Fig. 2: Connection Type Button

The icon can be in one of three states depending on the current connection status as shown below:

BlueTooth USB State Description
Disconnected The application is not connected to the scale adapter
Connecting The application is trying to establish connection to the scale adapter
Connected A connection has been established and the application is receiving position data

BlueTooth Connection

BlueTooth is the default connection method for the TouchDRO application. Although there is no further configuration needed within the application, the adapter must be paired with your Android device before use. The process might vary slightly depending on the Android OS version and device manufacturer, but in general, it consists of the following steps:

  1. From the top of the screen, swipe down once
  2. Long-press the BlueTooth connection button. This will bring up the BlueTooth settings page
  3. If needed, turn BlueTooth on (it is usually on by default)
  4. If needed, press the "Scan" button (in most cases the page will open and start scanning automatically)
  5. Wait for the TouchDRO adapter to appear in the list of Available Devices
    • New ESP32-based boards will appear as "TouchDRO"
    • Older boards and DIY kits will appear as "HC-05"
  6. Tap on the relevant entry in the list.
  7. The device will switch to "Pairing" mode and a dialog asking for a pass code will appear
  8. Enter "1234" (without quotes) and press "Enter" (the button text might differ on different devices/OS version)

If the pairing is successful, the new device will appear in the top part of the screen on the list of paired devices. Press the "Back" button to go to the main screen and open the TouchDRO application.

  1. In the top-right corner of the screen you will see a white BlueTooth icon; tap it once.
  2. This will bring up the "Select a Device" dialog that should now show the TouchDRO adapter you paired in the previous step.
  3. Tap on the device name to connect to it.

The icon will switch to the "Connecting" animation as the application tries to establish a connection with the BlueTooth transceiver. If the connection is successful, the icon will switch to a solid blue "Connected" mode and the application will play a chime.

To disconnect from the adapter, tap the connection button. The application will close the connection. It will beep four times and the icon will switch back to "Disconnected" mode (white BlueTooth icon)

If the connection fails, please refer to the "When Things go Wrong" section further down this page.

USB Connection

Supported USB Adapters

TouchDRO application can connect to a scale adapter using a USB-to-Serial bridge. There are a number of different options that include dedicated hardware devices, as well as some common microcontrollers running special firmware that emulates the "USB composite communication class" (AKA "USB CDC Class"). Unfortunately, most Android devices lack standard CDC drivers, so the implementation is left to the application developers. Consequently, the list of devices supported by TouchDRO is relatively limited and includes:

TouchDRO Configuration

In order to connect to a USB adapter, TouchDRO needs to be configured for USB connection mode. The setting is accessible on the main Application Settings page that is accessible from the left "drawer" menu.

There are two settings that need to be changed:

Once you go back to the main screen, you will notice that the connection icon now shows a white USB symbol. You can now connect your USB adapter to the tablet using a compatible USB cable.

The connection icon will switch to the "Connecting" animation while the application is trying to establish a connection with the adapter. Once the connection is successful, the icon will switch to the "Connected" mode showing a green USB symbol and the app will play a chime.

To disconnect from the adapter, tap the connection button. The application will close the connection. It will beep four times and the icon will switch back to "Disconnected" mode (white USB icon)

When Things go Wrong

No BlueTooth Devices in The List

The "Select a Device" dialog list is empty or the TouchDRO adapter does not appear on the list

This happens when the adapter is not paired with your Android device. Please refer to the steps outlined at the start of this page.

No USB Devices

TouchDRO supports only a limited number of devices. If the application can't find any compatible USB devices, it will show an error dialog similar to the one shown below.

Fig. 3: No USB Devices Dialog
Fig. 3: No USB Devices Dialog

If your device is plugged in and is working correctly but TouchDRO can't find it, it usually means that the device is not compatible. It could be using a different USB device driver or the vendor/device IDs are not allowlisted.

Connection Failed

The application shows "Connecting" icon animation for several seconds but then drops the connection and shows the dialog below.

Fig. 4: Connection Failed Dialog
Fig. 4: Connection Failed Dialog

This occurs when TouchDRO is unable to establish even a low level connection to the adapter. There are a few possible reasons:

Connection Timed Out

The application shows the "Connecting" icon for several seconds but then drops the connection and shows a dialog similar to the one below.

Fig. 5: Connection Timed Out Dialog
Fig. 5: Connection Timed Out Dialog

This usually means that the application was able to establish a low level connection with the BlueTooth transceiver or USB bridge, but did not receive any position data. The main two causes are:

Data Stream Stopped

The readouts switch to gray and after a few seconds the application closes the connection, beeps four times and shows a dialog similar to the one below.

Fig. 6: Data Stream Stopped Dialog
Fig. 6: Data Stream Stopped Dialog

There are two common causes for this error:

Connection Lost

The application abruptly switches from "Connected" to "Disconnected" state and shows the dialog shown below.

Fig. 7: Connection Lost Dialog
Fig. 7: Connection Lost Dialog

This can happen when the connection to the scale adapter is abruptly lost. Most commonly this happens when the USB device is unplugged or powered down without first disconnecting the TouchDRO application.