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USB FREQUENCY COUNTER AND VOLTMETER

Updated on 11.6.2015
Using PIC18F2550 for connecting analogue and digital signals to USB port . Included Visual Basic 6 code, Visual Studio 2005 C# code, PIC ASM code, PIC C code and a circuit diagram. The PIC microcontroller has 10 bit analogue to digital converter, by selecting 8 bits conversion the 2 LSB are ignored. The circuit is powered by the USB. The interface to the PC is HID class.
The frequency counter has a range of up to 4MHz (24bits). Inputs samplings can be done at rates of 1 per second and 1 every 0.1 second.
HID class (human interface device) is a class of devices like the mouse and the keyboard, the data transfer rate is limited to 64KB/S. The PC already has a driver for HID USB.
C# code is modified Microchip code from the USB framework, Microchip Solutions v2012-04-03.
VB6 code
includes guidance to setting up the PC. The PC register the PID and VID (product ID) of the USB device when it's plugged, the VB code uses these ID's to communicate with the device. For commercial VID it is needed to buy it from USB-IF, but in your lab you can use any number.
The source code is derived from freeware from these sources:
http://janaxelson.com/usb.htm , http://openprog.altervista.org/USB_firm_eng.html
You are free to use the circuit diagram and the VB software with no limitations.

The VB6 application is a combined digital and analogue voltmeter.

Circuit Description
See also Technical Tips

PIC18F2550
Pin 3 is the analogue input, voltage range 0 to 5V. Max input voltage is 5.5V .
Pin 11 is the counter input, TTL voltage levels.
Pin 14 is 3.3V internal supply for the USB transceiver. 0.22uF is required for regulation.
Pins 15,16 are the data lines to the USB connector on the PC.
Pin 20 is the PC 5V powering the PIC. It is limited to 100mA by the PC. 0.47uF is for decoupling.
For USB wiring info: http://www.interfacebus.com/Design_Connector_USB.html