PULL THE PIN CHALLENGE 16 HOW TO
PULL THE PIN CHALLENGE 16 SERIAL
PULL THE PIN CHALLENGE 16 CODE
PULL THE PIN CHALLENGE 16 FREE

The MM74C922N is a 16-key encoder that includes all the internals to take the output of a 16-key switch that we just saw from the previous step, and encode it onto only four outputs using a truth table.

PULL THE PIN CHALLENGE 16 HOW TO

First, let's see how to reduce the number of I/O pins this keypad is taking on our microcontroller. ' section, or map it to an array, which is just a couple of steps away. To do this, you need to either add more logic in your 'number pressed is. The numbers are their logical numbers from 0 to 15, not the actual number on the key that was pressed.

PULL THE PIN CHALLENGE 16 CODE

Here's pseudo code to show the flow: ROWS set INPUT COLS set OUTPUT for (ever) N.B. Other than that, I think it should be generally fine.

PULL THE PIN CHALLENGE 16 SERIAL

If you choose to use it you will have to modify it as I reference libraries that I wrote for serial communication. I've attached a file at the bottom that I wrote for this section to demonstrate direct connection and reading of the keypad. Depending on the speed of your MCU, you may have to tweek it a little, too. Through experimentation I found a workable delay rate, otherwise you'll get many many keypress notifications for each single keypress. Also of note is the issue of key debounce. If there is a one in there, then you have a keypress. Loop through each row, sending a logic 1 to the row and read the column pins. Set your row pins as output with initial logic 0 values. You'll note that there's no pin or hookup for power to the keypad, unlike the binary thumbwheel switch I talked about in a previous instructable. Your AVR probably has internal pull-ups, but the logic I had already come up with in my head didn't work well with that. I also had problems with my pins floating, so i used four 10k resistors to pull down the column pins to ground. Shy away from PD if you want to use serial communication on your arduino or other clone.

PULL THE PIN CHALLENGE 16 FREE

But for now, we're going to hook this sucker right into eight free I/O ports of our AVR. In the next steps I'll show you how you can reduce that to around four, maybe a couple more depending on how much control you want. Ok, first thing you'll notice is that we're going to be sucking up 8 I/O ports for this bloody keypad. Got your keypad setup? Good, we'll connect it to our microcontroller and start reading keypresses. Because I am a bone head and constantly worried that I'll hook up the wrong wires, i chose hookup wire of different colors and used the mnemonic for the visible spectrum ROYGBIV to choose my wire color from pin 1 to pin 8. Solder your wires to it, maybe throw on some shrink tubing and call that part a day. If you did attach a header, then mate it with the female 8-pin header (again, I just snipped off the right section from a long piece I had around). If you soldered your wires directly to the board then you don't have to worry about making a cable for it. The pictures below show the header soldered on. You can solder your wires directly to the pads if that suits you. Well, that's really all we need, isn't it? I first started by breaking an 8-piece section from a long male right angle breakaway header that I always like to keep lying around. Definitely no insert, just some markings on the cardboard outer part that described how the pins matched to columns. My keypad came in a package with hardly any information. Take your keypad an examine the bottom aspect for soldering pads.

8 pin right-angle header and matching female header for the keypad.

They sell for over $10-15 each online, but, again, I picked up 10 of these at my local electronics shop for $1.50 each. You can probably get away with ceramic if you have them already. I got a handful at my local electronics shop for $0.95 each. You can pick them up from or for around $5. Optional These parts aren't necessary for you to figure out how it works, but this instructable shows several different ways to connect this keypad and read data from it, so depending on the parts you want to do, you may or may not need the following.

hookupwire, soldering iron, wire cutters, etc.

The leading outlets carry them but they can tend to be spendy, so maybe try or do a search for '16-key keypad' on google. Just for the record, the firmware was written for an ATmega328p, so it should run well on that class of AVR's and probably many others with little to no modification. Of course, your custom own ghetto setup will suffice too. Arduino, Bare Bones Kit, Freeduino, Boarduino, and all the other clones work just fine. You can buy everything online, although I've found if you check your local electronic warehouse/shop (if you have one) you will be able to pick up everything considerably cheaper, though. This instructable doesn't have (m)any expensive components if you already have an AVR setup.

Pull the pin challenge 16