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Getting Started with Arduino – Chapter Twelve

This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Welcome back

This chapter we will spend some more time with the rotary encoder by using it to control a clock, look at ways of driving a common-anode LED display with Arduino, and make a usable alarm clock with which we can start to move from the prototype stage to an actual finished product – something you would be proud to give to someone.

So off we go…

In chapter eleven, we looked at getting some values from the rotary encoder. Not the easiest way of receiving user input, but certainly interesting. This week I have an example for you where the encoder is used for setting the time of a digital clock. This example is basically two previous projects mashed together. It consists of the LED digital clock from exercise 7.1, and the rotary encoder sketch from example 11.2. The sketch was quite simple in theory, but somewhat complex in execution. The idea was to read the decoder, and after every read, display the time. However, if the encoder’s button was pressed, the time set function would be activated. At this point, you turn the encoder in one direction to set the hours, and the other direction to set the minutes. Then press the button again to set that time and return to normal operations.

To recreate it you will need:

  • Your standard Arduino setup (computer, cable, Uno or 100% compatible)
  • Seven 560 ohm 1/4 watt resistors
  • Four 1 kilo ohm 1/4 resistors
  • Four BC548 NPN transistors (if you cannot find these, you can use 2N3904)
  • Two 74HC595 shift registers
  • DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
  • Solderless breadboard and connecting wires

Here is the sketch for your perusal, and the matching schematic (sorry, I forgot to add the DS1307 module – see example 12.2 schematic below for how to do this):

example12p1small

… in real life:

example12p1boardsmall

and a video clip:

After watching that clip you can soon see that there is an issue with the encoder. As a normal switch can bounce (turn on and off very very quickly in the latter part of operation), so can a rotary encoder. That is why it would sometimes return a result of clockwise, instead of anti-clockwise. Furthermore, they are right little pains when trying to use in a breadboard, so if you were going to use one in greater lengths, it would pay to make up your own little breakout board for it. Therefore at this stage we will leave the encoder for a while.

You may also have noticed the extra shield between the real time clock shield (yellow) and the arduino board. It is the Screwshield for Arduino – reviewed here. It is very useful to making a stronger connection to the I/O pins, or using normal multi-core wires.

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Next on the agenda is the common-anode LED display. Normally the LED display we have demonstrated in the past has been common-cathode, and very easy to use. Current would flow from the power supply, through the shift register’s outputs (for example the 74HC595), through current-limiting resistors, into the LED segment, then off to earth via the cathode. Current flows through a diode from the anode to the cathode, and finally back to earth/ground. For a refresher on diodes, please read this article. The other month I found this style of useful LED display:

clockdisplaysmall

Absolutely perfect for our clock experimentations. A nice colon in the middle, and another LED between the third and fourth digit which could make a good indicator of some sort. However the one catch (always a catch…) is that is was common-anode. This means that current starts from the power supply, through the common anode pin for the particular digit, then the LED segment, the LED’s individual cathode pin, through the current-limiting resistor and then to ground. With the current flowing in the opposite direction via a common anode, we can’t just hook the display up to our 74HC595 shift register.

Therefore, we will need the shift register to control switches to allow the current to flow through each segment, just like we have done previously controlling the cathodes of a common cathode display (see example 12.1). So to control the digits of this new display, we will need twelve switches (eight for the segments of the digit, and four to control the anodes). That would mean twelve BC548  transistors and 10k ohm resistors, and a lot of mess.

Instead we will now use the 74HC4066 quad bilateral switch IC. I have reviewed this chip being used with Arduinos in a separate article here. The 74HC4066 is quite a common chip, available from many suppliers including: element14/Newark (part number 380957), Digikey (part number 568-1463-5-ND) or Mouser (771-74HC4066N). If you cannot find them, email me and I can sell you some at cost plus postage. Once you have a understanding of this IC, please consider the following circuit:

example12p2schematic

Most of this should be easily understood. One shift register is controlling the anodes, turning them on and off via a 74HC4066. In past examples this shift register would have turned off common cathodes via a 10k resistor and an NPN transistor. The other shift register is controlling the individual LEDs for each digit via a pair of 74HC4066s (as they only have four switches per IC).

Here is the sketch, it should be quite a familiar piece of code for you by now.

To recreate it you will need:

  • Your standard Arduino setup (computer, cable, Uno or 100% compatible)
  • Seven 560 ohm 1/4 watt resistors
  • DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
  • Two 74HC595 shift registers
  • Three 74HC4066 quad bilateral switch ICs
  • Solderless breadboard and connecting wires
  • LED clock display module

And here is the result, with red and a blue display.

And the usual board layout:

example12p2boardsmall

The blue looks really good in a dark background. You can also get them in yellow and green.

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Moving along. Now and again, you often want to have a few buttons in use for user input, however the cheap ones don’t really like to sit in a breadboard. Naturally, you could make your own “button shield”, which would be very admirable, but then it would be preset to certain pins, which could interfere with your project. I had the same problem in writing this chapter, so came up with this example of an external “button panel” to make life easier. Here is the schematic, nothing complex at all – just four buttons and the required 10k ohm pull-down resistors:

example12p3schematic

and the finished product:

example12p3small

This was a quick job, as I will need to use a few buttons in the near future. Have also put some rubber feet on the bottom to stop the solder joints scratching the surface of the bench. Originally I was going to chop off the excess board at the top, but instead will add some LEDs to it after finishing this article. However using this button board will save a lot of frustration by not trying to jam the buttons into a breadboard.

pinsborder

Exercise 12.1

Now it is time for you to do some work. From this chapter onwards, we will be working on making a small alarm clock – something you could use. Just like the six million dollar man, we have the capability, the technology, and so on … except for Steve Austin. So this chapter, your task is to create and breadboard the  circuit and the underlying sketch. Using the LED display from example 12.1, your clock will have a menu option to set the time, alarm time, turn on and off the alarm, a snooze button – and also switch the display on and off (so you don’t stare at it when you should be trying to sleep).

You could either use a DS1307 module, or the raw parts. For an explanation of the circuitry, please see this post about making a RTC shield. You can always change it when we get to making a real prototype. The same with the Arduino – but for this exercise just stick with the normal board. Later on we will use a bare circuit the same as in chapter ten. With regards to user input, it’s up to you. A rotary encoder could be a real PITA, my example below just uses buttons. Anyhow, off you go!

Parts you will need:

  • Your standard Arduino setup (computer, cable, Uno or 100% compatible)
  • Seven 560 ohm 1/4 watt resistors
  • DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
  • Two 74HC595 shift registers
  • Three 74HC4066 quad bilateral switch ICs
  • Four normally open buttons or a board as described in example 12.3
  • Solderless breadboard and connecting wires
  • LED clock display module

Here is my interpretation of the answer to the exercise. Although this is a particularly long sketch for our examples, it is broken up into many functions which are quite modular, so you can easily follow the flow of the sketch if you start at void loop(). All of the types of functions used have been covered in the past tutorials. In then next chapters we will add more functions, such an an adjustable snooze, selectable blinking colon, and so on. If you have any questions, please ask.

The buttons have several functions. In normal clock display mode, button one is for menu, two turns the alarm on, three turns it off, and four turns the display on and off. If you press menu, button two is to select time set, three for alarm set, and four is like an enter button. When in the time/alarm set modes, button one increases the hour, button two increases minutes in units of ten, and button three increases minutes in ones, and four is enter. When the alarm activates, button four turns it off.

The schematic is just example 12.2 and example 12.3 connected together, however the first button on the external board is connected to digital pin 8 instead of 1.

So here is a photo of our work in progress:

exercise12p1boardsmall

And a video clip showing the various functions of the clock in operation:

I hope you found success and inspiration in this chapter. Now to Chapter Thirteen.

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Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in 4066, 74HC4066, arduino, COM-09117, COM-09481, COM-09483, education, learning electronics, lesson, microcontrollers, tutorialComments (11)

Getting Started with Arduino! – Chapter Eight

This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino microcontrollers. The first chapter is here, the complete index is here.

In this chapter we will continue to examine the features of the DS1307 real time clock, receive user input in a new way, use that input to control some physical movement, then build a strange analogue clock. So let’s go!

Recall from chapter seven, that the DS1307 is also has an inbuilt square wave generator, which can operate at a frequency of 1Hz. This is an ideal driver for a “seconds” indicator LED. To activate this you only need to send the hexidecimal value 0x10 after setting the date and time parameters when setting the time. Note this in line 70 of the solution for exercise 7.1. This also means you can create 1Hz pulses for timing purposes, an over-engineered blinking LED, or even an old-school countdown timer in conjunction with some CMOS 4017 ICs.

For now, let’s add a “seconds” LED to our clock from Exercise 7.1. The hardware is very simple, just connect a 560 ohm resistor to pin 7 of our DS1307, thence to a normal LED of your choice, thence to ground. Here is the result:

Not that exciting, but it is nice to have a bit more “blinkiness”.

Finally, there is also a need to work with 12-hour time. From the DS1307 data sheet we can see that it can be programmed to operate in this way, however it is easier to just work in 24-hour time, then use mathematics to convert the display to 12-hour time if necessary. The only hardware modification required is the addition of an LED (for example) to indicate whether it is AM or PM. In my example the LED indicates that it is AM.

Exercise 8.1

So now that is your task, convert the results of exercise 7.1 to display 12-hour time, using an LED to indicate AM or PM (or two LEDs, etc…)

Here is my result in video form:

and the sketch.

OK then, that’s enough about time for a while. Let’s learn about another way of accepting user input…

Your computer!

Previously we have used functions like Serial.print() to display data on the serial monitor box in the Arduino IDE. However, we can also use the serial monitor box to give our sketch data. At first this may seem rather pointless, as you would not use an Arduino just to do some maths for you, etc. However – if you are controlling some physical hardware, you now have a very simple way to feed it values, control movements, and so on. So let’s see how this works.

The first thing to know is that the serial input has one of two sources, either the USB port (so we can use the serial monitor in the Arduino IDE) or the serial in/out pins on our Arduino board. These are digital pins 0 and 1. You cannot use these pins for non-serial I/O functions in the same sketch. If you are using an Arduino Mega the pins are different, please see here.  For this chapter, we will use the USB port for our demonstrations.

Next, data is accepted in bytes (remember – 8 bits make a byte!). This is good, as a character (e.g. the letter A) is one byte. Our serial  input has a receiving buffer of 128 bytes. This means a project can receive up to 128 bytes whilst executing a portion of a sketch that does not wait for input. Then when the sketch is ready, it can allow the data to serially flow in from the buffer. You can also flush out the buffer, ready for more input. Just like a … well let’s keep it clean.

Ok, let’s have a look. Here is a sketch that accepts user input from your computer keyboard via the serial monitor box. So once you upload the sketch, open the serial monitor box and type something, then press return or enter. Enter and upload this sketch:

 

Here is a quick video clip of it in operation:

So now we can have something we already know displayed in front of us. Not so useful. However, what would be useful is converting the keyboard input into values that our Arduino can work with.

Consider this example. It accepts a single integer from the input of serial monitor box, converts it to a number you can use mathematically, and performs an operation on that number. Here is a shot of it in action:

example8p2

If you are unsure about how it works, follow the sketch using a pen and paper, that is write down a sample number for input, then run through the sketch manually, doing the computations yourself. I often find doing so is a good way of deciphering a complex sketch. Once you have completed that, it is time for…

Exercise 8.2

Create a sketch that accept an angle between 0 and 180, and a time in seconds between 0 and (say) 60. Then it will rotate a servo to that angle and hold it there for the duration, then return it to 0 degrees. For a refresher on servo operation, visit chapter three before you start.

Here is a video clip of my interpretation at work:

So now you have the ability to generate user input with a normal keyboard and a PC. In the future we will examine doing so without the need for a personal computer…

Finally, let’s have some fun by combining two projects from the past into one new exercise.

Exercise 8.3

Create an analogue clock using two servos, in a similar method to our analogue thermometer from chapter three. The user will set the time (hours and minutes) using the serial monitor box.

Here is a photo of my example. I spared no expense on this one…

exercise8p3small

Here is a video demonstration. First we see the clock being set to 12:59, then the hands moving into position, finally the transition from 12:59 to 1:00.

If you had more servos and some earplugs, a giant day/date/clock display could be made… Nevertheless, we have had another hopefully interesting and educational lecture. Or at least had a laugh. Now onto chapter nine.

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Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, education, LCD, lesson, microcontrollers, serial monitor, servo, tutorialComments (17)

Getting Started with Arduino! – Chapter Seven

This is part of a series titled “Getting Started with Arduino!” – A tutorial on the Arduino microcontrollers. The first chapter is here, the complete index is here.

Welcome back fellow arduidans!

This week is going to focus around the concept of real time, and how we can work with time to our advantage. (Perhaps working with time to our disadvantage is an oxymoron…) Once we have the ability to use time in our sketches, a whole new world of ideas and projects become possible. From a simple alarm clock, to complex timing automation systems, it can all be done with our Arduino and some brainpower. There is no time to waste, so let’s go!

First of all, there are a few mathematical and variable-type concepts to grasp in order to be able to understand the sketch requirements. It is a bit dry, but I will try and minimise it.

The first of these is binary-coded decimal.

Can you recall from chapter four how binary numbers worked? If not, have a look then come back. Binary coded decimal (or BCD) numbers are similar, but different… each digit is stored in a nibble of data. Remember when working with the 74HC595 shift registers, we sent bytes of data – a nibble is half of a byte. For example:

bcdtable

Below is a short clip of BCD in action – counting from 0 to 9 using LEDs:

However, remember each digit is one nibble, so to express larger numbers, you need more bits. For example, 12 would be 0001 0010; 256 is 0010 0101 0110, etc. Note that two BCD digits make up a byte. For example, the number 56 in BCD is 0101 0110,  which is 2 x 4 bits = 1 byte.

Next, we will need to work with variables that are bytes. Like any other variable, they can be declared easily, for example:

byte seconds = B11111;

B11111 is 31 in base 10, (that is, 2^4+2^3+2^2+2^1+2^0     or    16+8+4+2+1)

However, you can equate an integer into a byte variable. Here is a small sketch demonstrating this. And the result:

example7p1

If you printed off the results of the sketch in example 7.1, it would make a good cheat sheet for the Binary Quiz program in Chapter Five.

Anyhow, moving forward we now take a look at hexadecimal numbers. ‘Hex’ numbers are base-16, in that 16 digits/characters are used to represent numbers. Can you detect a pattern with the base-x numbers? Binary numbers are base-2, as they use 0 and 1; decimal numbers are base-10, as they use 0 to 9 – and hexadecimal numbers use 0 to 9 then A to F. Run the following sketch to see how they compare with binary and decimal.

Below is a screenshot of the result: the left column is binary, the centre decimal, and the right hexadecimal:

example7p1

Unfortunately the IC we use for timing uses BCD, so we need to be able to convert to and from BCD to make sense of the timing data. So now we have an understanding of BCD, binary, base-10 decimal, bytes, hexadecimal and nibbles. What a mouthful that was!

Coffee break.

Before we head back to timing, let’s look at a new function: switch… case. Say you needed to examine a variable, and make a decision based on the value of that variable, but there were more than two possible options. You could always use multiple if…then…else if functions, but that can be hard on the eyes. That is where switch… case comes in. It is quite self-explanatory, look at this example:

OK, we’re back. It would seem that this chapter is all numbers and what not, but we are scaffolding our learning to be able to work with an integrated circuit that deals with the time for us. There is one last thing to look at then we can get on with timing things. And that thing is…

The I2C bus.

(There are two ways one could explain this, the simple way, and the detailed way. As this is “Getting Started with Arduino”, I will use the simple method. If you would like more detailed technical information, please read this document: NXP I2C Bus.pdf, or read the detailed website by NXP here)

The I2C bus (also known as “two wire interface”) is the name of a type of interface between devices (integrated circuits) that allows them to communicate, control and share data with each other. (It was invented by Philips in the late 1970s. [Philips spun off their semiconductor division into NXP]).  This interchange of data occurs serially, using only  two wires (ergo two wire interface), one called SDA (serial data) and the other SCL (serial clock).

nxpi2cbussmall

I2C bus – image from NXP documentation

A device can be a master, or a slave. In our situation, the Arduino is the master, and our time chip is the slave. Each chip on the bus has their own unique “address”, just like your home address, but in binary or in hexadecimal. You use the address in your sketch before communicating with the desired device on the I2C bus. There are many different types of devices that work with the I2C bus, from lighting controllers, analogue<> digital converters, LED drivers, the list is quite large. But the chip of interest to us, is the Maxim DS1307 Serial I2C real-time clock. Let’s have a look:

ds1307small

This amazing little chip, with only a few external components, can keep track of the time in 12-and 24-hour formats, day of week, calendar day, month and year, leap years, and the number of days in a month. Interestingly, it can also generate a square wave at 1Hz, 4kHz, 8kHz, or 32 kHz. For further technical information, here is the DS1307 data sheet.pdf. Note – the DS1307 does not work below 0 degrees Celsius/32 degrees Fahrenheit, if you need to go below freezing, use a DS1307N.

Using the DS1307 with our Arduino board is quite simple, either you can purchase a board with the chip and external circuitry ready to use, or make the circuit yourself. If you are going to do it yourself, here is the circuit diagram for you to follow:

  ds1307exampleuse
 

The 3V battery is for backup purposes, a good example to use would be a CR2032 coin cell – however any 3V, long-life source should be fine. If you purchase a DS1307 board, check the battery voltage before using it…. my board kept forgetting the time, until I realised it shipped with a flat battery. The backup battery will not allow the chip to communicate when Vcc has dropped, it only allows the chip to keep time so it is accurate when the supply voltage is restored. Fair enough. The crystal is 32.768 kHz, and easily available. The capacitor is just a standard 0.1uF ceramic.

Now to the software, or working with the DS1307 in our sketches. To enable the I2C bus on Arduino there is the wire library which contains the functions required to communicate with devices connected to our I2C bus. The Arduino pins to use are analogue 4 (data) and analogue 5 (clock). If you are using a Mega, they are 20 (data) and 21 (clock). There are only three things that we need to accomplish: initially setting the time data to the chip; reading the time data back from the chip; and enabling that 1Hz square-wave function (very useful – if you were making an LED clock, you could have a nice blinking LED).

First of all, we need to know the I2C address for our DS1307. It is 0x68 in hexadecimal. Addresses are unique to the device type, not each individual device of the same type.

Next, the DS1307 accepts or returns the timing data in a specific order…

  • seconds (always set seconds to zero, otherwise the oscillator in the DS1307 will stay off)
  • minutes
  • hours
  • day of week (You can set this number to any value between 1 and 7, e.g. 1 is Sunday, then 2 is Monday…)
  • day of month
  • month
  • year
  • control register (optional – used to control the square-wave function frequency and logic level)

… but it only accepts and returns this data in BCD. So – we’re going to need some functions to convert decimal numbers to BCD and vice-versa (unless you want to make a BCD clock …)

However, once again in the interests of trying to keep this simple, I will present you with a boilerplate sketch, with which you can copy and paste the code into your own creations. Please examine this file. Note that this sketch also activates the 1Hz square wave, available on pin 7. Below is a quick video of this square wave on my little oscilloscope:

This week we will look at only using 24-hour time; in the near future we will examine how to use 12-hour (AM/PM) time with the DS1307. Here is a screen capture of the serial output box:

example7p3

Now that you have the ability to send this time data to the serial output box, you can send it to other devices. For example, let’s make a simple LCD clock. It is very easy to modify our example 7.3 sketch, the only thing to take into account is the available space on the LCD module. To save time I am using the Electronic Brick kit to assemble this example. Below is a short clip of our LCD clock operating:

and here is the sketch. After seeing that clock fire up and work correctly, I felt really great – I hope you did too.

Update – for more information on the DS1307 real-time clock IC, visit this page

Now let’s head back in time, to when digital clocks were all the rage…

Exercise 7.1

Using our Arduino, DS1307 clock chip, and the exact hardware from exercise 6.2 (except for the variable resistor, no need for that) – make a nice simple digital clock. It will only need to show the hours and minutes, unless you wish to add more display hardware. Have fun!

Here is my result, in video form:

and the sketch. Just an interesting note – after you upload your sketch to set the time; comment out the line to set the time, then upload the sketch a second time. Otherwise every time your clock loses power and reboots, it will start from the time defined in the sketch!

As mentioned earlier, the DS1307 has a square-wave output that we can use for various applications. This can be used from pin 7. To control the SQW is very easy – we just set the pointer to the SQW register then a value for the frequency. This is explained in the following sketch:

And here it is in action – we have connected a very old frequency counter to pin 7 of the DS1307:

And there we have it – another useful chapter. Now to move on to Chapter Eight.

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Have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, BCD, ds1307, education, hexadecimal, I2C, LCD, lesson, microcontrollers, tutorialComments (35)


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