Buttons
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You can have buttons in all sizes and shapes. You can have square momentary switches soldered directly to holes on the PCB, SMD micro switches soldered directly to solder pads on the PCB, big round external buttons soldered with wires to the PCB, illuminated buttons, etc. Mostly buttons only connect to electronic circuits to each other and thus polarity isn't an issue.
By default on the display module we use 1 normal tactile push button of 6 x 6 mm. It is advisable to choose a height which is suitable for your enclosure (if you use one). Another solution is to create an mechanism that presses the button when you press that mechanism on the outside of your enclosure. When you don't use an enclosure I would advise to use a button of a default 5 mm height.
The button fits only in 2 ways and both are fine. The legs of the button do fit on the top and bottom of the button mark on the display module PCB right below the text BTN_SEL. The only other way it does fit is to rotate the button 180 degrees. In this way the button will still work correctly.
Mostly the button will fit quite well and you can solder the button on the backside without addiitional support. If you want to add some extra support you can bend the legs to close to the PCB. In that case I advise to bend it inwards to the the opposite 2 legs.
If there would not be other connection methods for a button and you want to connect an external button instead of onboard you can solder a wire to 1 of the 2 left holes of BTN_SEL and 1 wire to 1 of the 2 right holes of BTN_SEL. These 2 wires should be connected to the 2 contact pins of the external button. On the display module PCB we made it a bit easier for you: you can connect the 2 wires to BTN_SEL + and BTN_SEL - at the bottom of the PCB.
Both the main PCB and the display module use angled tactile push buttons. On the display module they are optional since there are options to conenct other types of buttons. And actually on the main PCB you can also decide to use other buttons.
The angled tactile push buttons I use are 6 x 6 x 5 mm. When you use an enclosure you should pay attention to the height of the button whether it is long enough or not to be able to reach on the outside of the enclosure.
The angled buttons do fit only in one wat. 2 supporting legs do have more width between each other than the 2 contact legs. The same difference can be spot on the places on the PCB's where you can solder the buttons.
Again when you want to strengthen the support you can bend the support legs inwards to each other. You should not bend the contact legs of this kind of buttons.
If there would not be other connection methods for a button and you want to connect an external button instead of onboard you can solder wires to the 2 holes that are closer to each other. These 2 wires should be connected to the 2 contact pins of the external button. On the display module PCB we made it a bit easier for you: you can connect the 2 wires to BTN_UP + and BTN_UP - at the bottom of the PCB for the up button and to BTN_DWN + and BTN_DWN - on the bottom of the PCB for the down button.
In fact illuminated buttons do not have a big difference to other types of buttons. The only difference is that they have some extra pins to connect the power for the led inside the buttons. This is why should have a good look to all pins on the button. Mostly there are small marks which describes the function of each pins. The marks mostly can be seen barely. You might need a magnifying glass and good white light to see them. For the button part of the illimunated button polarity doesn't matter but for the led part polarity does matter! The ground of the led and the ground of the button can be connected to each other so that you would only need 3 wires: 1 common ground, 1 positive signal for the button part and 1 positive signal for the led.
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