Today’s project is pretty simple, just testing out some logic level conversion. I have another project where I’m attempting to drive a controller-less LCD module that requires a pretty high refresh rate, so I’m implementing the logic on the Papilio FPGA board. The only hurdle is that the Spartan3 has 3.3V outputs, and the LCD module requires 5V logic. Since my logic is only one-directional, I figured the easiest way would to just find a 5V part that an ‘on’ voltage less than 3.3V. So I grabbed some of these Octal Bus Buffers. According to the datasheet, the minimum high input is only 2V. As a quick test, I got a dual 3.3/5 breadboard power suppply, one of the 74ACT244s, and a 555 timer. I setup the 555 for astable mode to generate a square wave to feed in to the buffer, so I could compare the input and output voltages on the ‘scope. I used the 3.3V to power the 555 and the 5V rail to power the buffer.
I applied power, and it worked perfectly, 3.3 in, 5 out.
As you can see, nothing fancy, but a cheap and easy way to drive a 5V part from a 3.3V controller. Hopefully soon I’ll be able to show these guys in action helping to drive an old surplus 640 x 480 LCD.