Really Big (bigger) Displays the 240 X 320 Color TFT
About two years ago I bought several of the 240 X 320 displays and immediately was struck by how much information can be displayed on the face of the unit and like a choice of 256K colors. Lots of customization can be had here. Unlike the 128 x 128 or 128 X 160, which I used straight into the Arduino pins, these larger displays Do Not Like to see 5 VDC.
They like to see 3.3 VDC and typically a “Level Shifter” must be interjected between the 5 volt Arduino Pins and the pins on the display which like to see 3.3 VDC. So this is where I get emails about running the Arduino at 3.3 VDC and then no level shifting is required. Not sure my heart is that strong to do that. The literature abounds with tricks and tips to do the level shifting.
One method involves a series resistor combination of a 4.7K in series with a 10K (the 10K other end is at ground). Now to the high level math. If you ran 5 VDC through the 14.7K resistor( 4.7K + 10K) the current via ohms law would be 5/14.7K = .340 milliamp . Now a bit more math .340 milliamp flowing through 10K would be a voltage drop of 3.4 volt and the drop across the 4.7K would be 1.6 volts. So at the junction of the 4.7 K and 10K you would read 3.4 VDC. Thus one end of the 4.7K is connected to the Arduino pin the junction connection of the 4.7K and 10K is peeled off to the display and the other end of the 10K goes to ground. Instant level shifter. You would need 6 such combinations of 4.7K and 10K resistors.
Another way is to take an IC such as a hex buffer IC such as the CD4050 and by connecting 3.3 VDC to Pin 1 (Vdd) all inputs to the IC (six total) are outputted at 3.3 VDC. Many of the wing nut jobs hate this approach because it is not bi-directional. There are bi-directional level shifters but cost more than the nominal 50 cents for the CD4050. In my application I only need a single direction and that is a down shift. Below is the pin out for the CD4050
Here is the display and you will get a sense of the size with the ease of readability. Did I mention about the 256K color choices?
So now the problem is since the CD4050 level shifter will be used –how do you hook up the display? A glib answer would be carefully! Shown below is a hand sketch of the Nano ICSP and a decode of the pins on the back of the display. Note Vcc is connected to 3.3 VDC not 5 VDC as shown on the sketch.
So yes many will have trouble connecting the dots so the magic decoder ring is provided below. Please no inquires about how to connect the output of the Si5351 –CLK0 is the LO and CLK2 is the BFO.
73’s
Pete N6QW
