The 4x4 Keypad is technical speaking just 16 buttons. Usually you will need one digital input pin for each button which is connected to ground or voltage. So you will need 16 digital input pins plus a common ground/voltage. But the keypad has only eight connectors. How does this work?
The Matrix
The first four pins are connected to all buttons row-wise. The last four pins are also connected to all buttons, but column-wise.
So the first pin has a connection to button 1, 2, 3, A, the second pin to 4, 5, 6, B and so on.
And pin five (the first pin from the other group) is connected to button 1, 4, 7, *.
Keypad matrix
How to read a button-press
In simple terms: if you can measure a connection between pin 2 and pin 6, button 5 is pressed.How can we realize it with an Arduino? You connect all eight pins to digital pins of an Arduino. Declare the first four pins as output pins (that would be the pins, responsible for the rows) and the last four pins as input pins (aka the columns). Then you would pull each of the output pins high (one after another) and read all the input pins. So you pull pin 1 HIGH and read pins 5 to 8. Then you pull pin 1 LOW again and pull pin 2 to HIGH. Again reading pins 5 to 8. You have to continue with pin 3 and 4. And if none of those input pins get a positive reading - you know no button is pressed. Otherwise you know exactly which button was pressed.
Since the Corona virus (Covid-19) caused a worldwide pandemic, we became aware how important it is to wash our hands properly. You should wash your hands for at least 20 seconds with soap. How to measure it? You can use your wet hands to start the stopwatch on your smartphone - not ideal. Or you can sing "Happy Birthday" twice. Well, this might be a little awkward. And if you are in hurry, you can sing the song much faster. I managed to sing two times "Happy Birthday" within 12 seconds. It would be nice to have a timer, that you can start touch-less. But it must look cool somehow. I remembered the classic SiFi movie Demolition Man (1993). Which takes place in 2032 and instead of toilet paper the people are using the three seashells. This would make a nice timer.
The parts
Most of the parts are somehow leftovers. The plastic box was a box containing chocolate sweets. I used three Neopixels from an old strip. The plastic seashells where also a sweet I know from my younger days. In German it is called "Schleckmuschel" or simply "Leckmuschel". Which both can hardly translated into English. Literally it would be "Seashell to suck" or "Seashell to lick". But I think the closest would be "Toffee in a Seashell". It was on sale as a retro campaign. A cheap IR proximity sensor and all of this controlled by an Arduino Nano.
The build
To remove the candy from the seashells, I could licked them, till they are clean. But first of all this would have taken ages and it tasted not as good, as when I was a kid. So I soaked them in warm water for quite a while until the toffee was vanished into the water. I needed a box for the controller, the sensor and the three seashells to fit on top of it. An empty box of candy will do. Just cut a hole for the sensor to reach though. The controller, the sensor and the connection for the Neopixel get their own PCB prototype board. Now gluing the Neopixels and the seashells on the top of the box and connecting everything. I choose to power everything with a small USB powerbank, which is connected to the USB port of the Nano. Usually I would connect the power rails of the Neopixel stripe directly to the power source. But since this are only three pixels, I have no hard feelings about connecting it to the 5V output pin of the Arduino.
Friends of mine are about to celebrate their 50th anniversary. And both love colorful, blinking LEDs like I do. So I decided to make a glowing heart for them. Since I'm only creative but not an artist, I never wasted a thought about creating the heart shaped form for myself. After hours of research, I found a heart made of wooden branches, that fits my needs.
The build
I used a 60 LEDs / meter Neopixel strip. I figured out that if I placed them on the inner side of the heart, I'll need about 48-49 Pixels. Well, with a little overlap I can make it 50 to honor the 50th anniversary. Since the strip's adhesive tape won't stick on the wooden surface, I additionally fixed it with some thread. That took about 10 minutes. I put the controller in one of those electrical installation boxes.
The Programming
I thought about using an ESP as a controller, but it shouldn't be too fancy. So I used an Arduino Nano. That limits the program to a few kbs. So I made ten different animations. Tried to be very efficient and flexible. The animation, I'm most proud of is the beating heart. I tried to use real heartbeat timings for this. And since the 50th anniversary is also called the golden wedding, I made three modes with only golden colors. And to change the modes, I implemented a push-button.
One of the modes is quite special. I made an animation, that simulates a heartbeat. For this I investigated how the correct timing for the heartbeat is and tried to implement it as accurately, as I can. Which worked out pretty well.
The couple is quite happy with the present. In fact, after three month they are still enjoying it - which is longer than most of my relationships last.
Elegoo Industries contacted me and asked me if they should send me one of their toy-robots and I could do a review of it. I agreed under the condition, that I would do an honest review. They agreed and sent me the Elegoo Robot Mini car.
The Assembly
The car comes with a detailed assembly instruction printed on a huge piece of paper. But since it's marked as suitable for children, it should be possible for me to put those pieces together without it. And with a little trial and error, I could assemble the car within half an hour without reading the instructions. After that I checked, if I missed something out. I forgot the screws for the battery holder. Other than that - the assembly was quite self explanatory.
The Hardware
Well the complete chassis is made of plywood. With the controversy of the excessive waste through plastic, it's a good alternative. It really fells good and looks nice.
It has an Arduino Nano as controller, a Bluetooth adapter, light and distance sensor, a piezo speaker, three Neopixels, two geared motors, a motor driver and a Li-Io battery pack. So could start playing with it, without buying additional components. It has also a cable and pin-headers you can put on the roof of the car. So you could add additional sensors or LEDs to the car without opening it up again.
The Software
A preset of several functionalities are already uploaded to the controller of the Elegoo car. It has a line-following mode, an obstacle avoidance mode, a following mode and can be controlled with an app, that you have to install on your smartphone or tablet. So it should be playable right out of the box. You can download the complete source code for the robot from the Elegoo Website. That has the advantage that you don't have to reinvent the wheel. You can add functionalities or modify the existing ones.
The line following mode didn't work as expected. The avoidance mode works, but still can be improved.
The App
For remote controlling the robot, I downloaded the App from the PlayStore. Unfortunately I could not connect to the car. I've tried two different Smartphones and a tablet. None of them wanted to be connected to the car. So I can't really tell how good or bad the App is.
Video
Images
In short
What I like
I like, that you can download the car's software and chassis. So you can customize the car as you like. But you don't get a naked construction kit. So even when you are new to the robot building topic, you'll get something you can work with. It already has some functionality. You can see how other solve problems. I would recommend this robot over construction kits, where you get all the parts and have to develop software and logic for yourself.
What I don't like
If the preinstalled software promises several functionalities, I would have expected them to work somehow. The line-following mode didn't work at all (see video). And I couldn't use the app because the car won't pair with my phone.
All in all, I think if you want to build and program your first robot, you should go for the Elegoo Robot Mini Car. The 35 € are good invested.
