Pseudo 7-Segment Display on a 128×64 pixel OLED

Downloads appear at the end of this post.

Graphic image of a display device showing large and small numbers.
128×64 Pixel OLED showing the time on a simulated 7-segment display.

I’ve mentioned in a previous post that I’ve started to use MicroBlocks (https://microblocks.fun/) to write programs for the Raspberry Pi Pico. It comes with an OLED extension library which allows text and numbers to be written to the screen. The commands control the simple 128×64 I2C displays, which can be easily connected to Pins 4 and 5 on the Raspberry Pi Pico.

One thing that I noticed, however, is that the size of the standard text is really a bit small for my eyes now, so I wanted to see if I could write a small set of functions that would change the size of digits on screen, by simulating a 7-segment display.

I remembered that a 7-segment display starts with a simple diagram that names each segment with a letter. In the standard layout, segment “a” is at the top, and then the segments clockwise from here are “b” through to “f”, with the central segment being “g”. In order to store this using MicroBlocks, I needed a list.

It took me a little while to get my head around this. Digit 0 needs all of the segments except the central one. Digit 1 needs segments “b” and “c”. In MicroBlocks however, the lists start at item 1, which meant that I had to remember to take account of this later.

The next step was to create a function that looked that the digit required, decide which segments are turned-on or turned-off and draw these as rectangles on the screen using the OLED library commands. If there is an “a” in the SegmentList, then it is drawn on the OLED pixels, and if not, it is erased. I defer updating the OLED pixels until all of the segments have been drawn so that there is no flicker.

Part of the routine for drawing the segments

Once I had the main functions written, it’s a relatively simple task to use them to show large digits on the screen. I had to use modulo and division mathematical functions to separate out the units, tens and hundreds, and then shift the XPosition of each segment before display.

Downloads

There are two MicroBlocks programs ready to download:

Counting to 999 on an OLED display (7SegmentDisplay.ubp)

Real-time clock and large simulated display (LargeDisplayClock.ubp)

Advertisement

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s