Adding Bluetooth Modem to the dual channel digital voltmeter

Wichit Sirichote,

Adding Bluetooth Modem to the digital voltmeter enables smartphone to gather the analog signal easily.

The Dual channel digital voltmeter built with ICL7135 is very flexible for analog signal gathering through the RS232 port. For some applications that needs wireless between the meter and the host device, we can use the bluetooth modem for wireless connection easily. Benifit of using bluetooth modem is to enable the smartphone to be a host device for analog signal recording.
Figure 1: Bluetooth MODEM with dual channel digital voltmeter. 

The modem has builtin +3.3V regulator and status LED. VCC must be +5V from the microcontroller power supply. Since the microcontroller is +5V logic, to drive the RX pin of the Bluetooth chip with +3.3V logic, we insert 1k resistor from TX pin of the microcontroller.
Figure 2: wiring circuit. 

I used 4-wire ribbon cable for connecting the MODEM to the microcontroller.
Figure 3: The bluetooth modem is placed at front panel with small hole for connect LED.  

Simple and very easy for bluetooth installation.

Connecting the voltmeter to a PC with Bluetooth is done by Windows automatically.
Figure 4: Adding Bluetooth device to the PC.

The Wizard will search the device and ask for pairing code.
Figure 5: Searching bluetooth device. 

  Enter tye passkey 1234.
Figure 6: Enter the passkey 1234.

Windows will assign the available COM port for data communication.

Figure 7: Complete connection by assigning the available COM port. 

We can use tera terminal for connecting our meter with COM4 then.

Figure 8: Using teraterm with Bluetooth.

When press "?" key, the meter will display the help menu.

Figure 9: Display commands in help menu. 

We can also use the smart phone for connecting the voltmeter. Shown scanning and found the G6-Data-Logger-V3. The device name can be programmed using AT mode. The datasheet of the bluetooth explains how to use AT commands.
Figure 10: Using smartphone for connecting the voltmeter. 

Enter PIN number, 1234 for pairing.
Figure 11: Enter PIN number 1234.  

Example of using Bluetooth serial controller to record the data stream.

Figure 12: Using Bluetooth Serial Controller.

You can find many applications for Bluetooth terminal from Google serach.

Figure 13: Applications for Bluetooth terminal.

Download Bluetooth MODEM datasheet


24 January 2016