YourITronics

Adding a cheap LCD to your PC is a popular diy project for many beginners in electronics. The parallel port however, is dead. It’s obsolete. It’s big…ugly and just awful. The solution? Add a USB interface to your existing LCDs. The circuit interfaces to a standard HD44780 compatible LCD and emulates the CrystalFontz serial protocol over a virtual COM port created by the FTDI chip. This enables you to use already existing software to speak to the LCD, for example the popular program LCD Smartie. The circuit uses an AVR microcontroller, the Atiny2313, and a USB chip from FTDI. The usb chip creates a virtual COM port on the computer. It has an external EEPROM programmable via USB to store information and settings. You can for example have the chip report back the name of your project when you plug it in. Very neat.

The backlight and contrast can be controlled from the computer. They are each connected to one of the PWM outputs on the AVR. Since the CrystalFontz protocol support software control of contrast and backlight, this seemed like a nice feature to add. Only LED backlights are supported, no EL backlights. The backlight can be powered from the USB port if its current draw is less than about 420 mA. If you need more, an external supply can be connected.

LCD USB interfacing: [Link]

The module uses an inexpensive 8 bit Temperature Sensor the TMP37 from Analog Devices.Since the data was analog and the PIC16f84 does not have an analog input,an external ADC had to be used.Texas Instruments’ TLC549 was chosen for this.The advantage of this ADC was that it could communicate with the microcontroller serially.You may also use similar ADCs from Maxim-IC.The LCD is a normal 16×2 display which uses the Hitachi Controller HD44780.

PIC16F84A temperature controller: [Via] - [Link]