Week 10: Output Devices
Group Assignment: measure the power consumption of an output device
Individual Assignment: add an output device to a microcontroller board you've designed, and program it to do something
OLED SSD1306
Getting Started
A display is a very important output and potentially helpful for my project. Our lab has this display available. It measures 0.96 inches (diagonally), and has display colors of yellow and blue.
Dr Neil shared a similar board he made, using this display and the ATTiny45 as the microcontroller. It appear that he has exactly the same module as we do, same 4 pins, and coloring as well.
Here are the traces for that same board. This is very helpful to get started, thanks Dr. Neil! Examining the board in further detail, we notice a couple other components we must make sure to include in our schematic. First of all, there are pull-up resistors on the SDA and SCL lines. This is needed because the microcontroller can only pull the lines low, but can't drive them high. We also note a capacitor which can be placed between Ground and VCC. When using the OLED its good to have a capacitor since the power requirements are not stable, when the screen is cleared or new elements put on display, the power requirements will increase for that moment.
Our next task is to choose an appropriate board. We do not have the ATTiny45, however we do have the ATTiny1614. Just because we have a board, however, doesn't necessarily mean its a good choice. However, looking at the data sheet, and examining the schematic we see that it has the appropriate pins for the task and communication. We all understood why it is called 1614.
We must also ensure that appropriate libraries are there for the microcontroller to deal with the device in question, here the OLED SSD-1306. Research brought us to discover the U8g2 library, which was easy to install, and should be helpful.
Designing and Creating the Board
Following the usual procedure, we start with the schematic. Besides the ATTiny, we'll need 4 holes for the OLED, 6 header pin for programming and then just a few other components noted above (2 resistors and a capacitor).
Then the PCB editor, check the design rules. We checked, we pass, except for the 4 holes, but they are special as we will be inserting the SSD1306 module right there.
Finally, check out the 3D view! All the components are present. Looks normal.
Now as usual we use gerber-to-png tool to prepare for milling. There will are 3 files we'll need to use for that process: the traces, the drill, and the outline. We'll run them in that order on the machine using Mods. If you look carefully, in the screenshot below, you'll see that there are no drill holes in the drill file. That's because in the file the holes for drilling are only 0.75 mm across, however this is not possible where the bit is 1/32"=0.79 mm. We changed that later.
The board was cut properly, we gathered the other components, and now ready to solder!!
Programming the Board
We'll program in the Arduino IDE. Setting up we need to change a few things under 'Tools'.
Here is the first (very basic) program. It uses the U8g2 library which we installed earlier.
S.I.B.I.N. is a cool character, he showed me Lopaka. Lopaka is a cool website that helps you write code for such displays using the U8g2 library. You can draw, enter text, insert images - and it generates the required code!! So cool.
One of the next obvious things to do is loop text, and in the program below we successfully do it. Scrolling left to right because we read from left to right, at least in English. There are a few issues. One issue is the speed. It's slow even with delay at 1 ms. To solve this we increment the pixel displacement in each iteration by 3 instead of 1. That makes it 3 times faster. Another issue is to know how far we need to scroll. In other words, it is not clear the total length in the X-direction of a custom message. We use trial and error.
Check out the result and Follow MakerKootam!
Files
Gerber files for OLED board.NEMA17 Stepper Motor
Research and Background
Rayan has some great documentation for the NEMA17 stepper, including a brilliant schematic diagram and other resources.
Brief background on NEMA17 Stepper motor. It is a standard stepper motor commonly used in a wide variety of different machines but perhaps most famous for use in 3D printers. It is called 17 because it is a block with square head measuring 1.7 inches. It comes in both 4 and 6 wire varieties, but we have the 4-wire type which is great because that's easier. Each step measures 1.8 degrees, so a full rotation consists of 200 steps.
We'll also need a motor driver to use with the NEMA17, which will determine how and when the motor will rotate. The ideal and common type, which we also have available, is the DRV8825 shown here. It can control the speed and direction of the stepper motor with only 2 pins!! STEP controls the steps, DIR controls direction.
Furthermore, this driver can control even smaller steps, called microstepping. The following logic table details various the different microstep resolutions for given values on pins M0, M1, M2. Hence we see this driver provides a great degree of control over our stepper motor. However, that is not necessarily important to immediately implement as we just get started.
What is very important to see, understand is the pinout for the DRV8825, like this. Note RST is Reset, SLP is Sleep. M0,M1,M2 are for microstepping which we don't need in our first board. Rest should be self-explanatory.
STEP and DIR are the important pins controlling the speed and direction.
This tutorial was very helpful in my understanding. Thanks respect, and credits for pinout diagram.