USB Voltmeter Specifications
Voltage Input Range: 0 - 500V
Voltage Input Channels: 2
Voltage Resolution: 10mV
Power Supply: 5V (USB Powered)
PCB Dimensions: 18mm x 59mm / 0.7" x 2.3"
USB Voltmeter Component List
Programmed PIC18F2550 Microcontroller
USB Voltmeter PCB
12-PIN Gold Plated Header
8-PIN Gold Plated Header
28-PIN IC Socket
USB Type B Connector
20MHz Crystal Resonator
C1 - 470n Capacitor (474)
C2 - 100n Capacitor (104)
C3 - 10uF / 35V Capacitor
R1, R2 - 10K Micro Resistor (brown black orange gold)
R3, R4 - 100K 1% Resistor (brown orange black black brown)
R5, R6 6.8K 1% Resistor (blue gray black brown brown) for measuring voltage up to 70V
R5, R6 1K 1% Resistor (brown black black brown brown) for measuring voltage up to 500V
USB Voltmeter PCB Layout
Installing USB Voltmeter Drivers
1) Download and unzip USB Voltmeter drivers
2) Connect USB Voltmeter board to a computer using standard USB cable.
3) Windows will issue a prompt to install drivers. Point it unzipped drivers.
Windows 2000 / XP
Under Windows 2000 or XP you will be prompted twice to install two drivers. On the first prompt browse and point to MCHPUSB driver folder. On the second prompt browse and point to USB CDC driver folder.
Windows 7 / VISTA
Under Windows 7 or VISTA you might be only prompted once to install USB CDC driver if MCHPUSB driver is already installed.
USB Voltmeter Software
After USB drivers are installed launch USB Voltmeter software. As soon as USB Voltmeter board is plugged in USB Voltmeter software will automatically establish connection with the COM port in the background and display voltage readings from both input channels.
USB Voltmeter Software Calibration
For highest accuracy, readings from both input channels can be calibrated via Voltmeter software. Pressing ESC key within the software will bring up similar window for each channel.
If measuring voltage up to 500V install 1K resistors for R5 and R6. The default calibration value for 1K resistors is 0.67
If measuring voltage up to 70V it is recommended to install 6.8K resistors for R5 and R6. Doing so will provide higher stability and voltage resolution in the decimal values. The default calibration value for 6.8K resistors is 0.0999
After the calibration values are entered hit Enter key or click on OK button to save the settings.
For highest accuracy calibration value can be slightly increased or decreased. Simply connect a known voltage to an input and match voltage of USB Voltmeter to a commercial voltmeter.
USB Voltmeter Board Schematic
USB Voltmeter Kit
USB Voltmeter kit with programmed PIC18F2455 / PIC18F2550 microcontroller and USB Voltmeter software is available at Electronics-DIY
store. Please see the link for more details.