Hi There!
I am trying to accomplish this project for school.
The main issue is as to where to plug all of the wires in. It doesn’t specify how to connect the Real Time Clock, the SN74HC138N, or any of the AM/PM LEDs.
I am using a standard Arduino Uno.
The project is due on Tuesday (13/10/2015).
Thanks for your help!
Hi,
What is your electronics, programming, arduino, hardware experience?
Is this a school/college/university project?
If you want to make the complete system as shown, you won't be getting any sleep.
Its not just plug and play, even though they give you the sketch.
You need some digital electronics experience to understand how to connect it all together for a start.
Tom..... 
I'm pretty new to all of it.
I was hoping it was all just plug and play so to speak...I've already purchased all of the parts 
It's a year 10 project.
This is a complicated project for someone who is "pretty new to it all". It's not going to be plug and play.
One of the skills you will learn as you go, is to break down a complex problem into smaller more manageable bits. You may not get the project completed by next Tuesday, but if you break it down, you will be able to demonstrate a good start and an understanding of what it will take to complete.
You have the advantage of using adafruit devices and there is pretty good documentation available through adafruit, on the web, and through searching this forum.
First, I would recommend learning how to read the current time from the chronodot and display it on the serial monitor.
Second, I would learn how to use one seven segment display and the associated library, and display the month and day on it.
Third, I would learn how to use three seven segment displays with 3 different i2c addresses which you will have to set on the backpack. Display the current time (month-day-year-hour-minute) on the three displays.
When get to this point, it will be a good accomplishment, and I'm sure you will have worked through several problems.
I think you have a choice of what to do next.
After you get the one line display completed, you could chose to tackle the SN74HC138N and figure out how to address the 9 displays. This is likely to be the most complex part of the project.
You can address up to 8 displays by just setting the i2c address jumpers similarly to what you did on the first three. So, you could add a second line (like destination time) without having to use the SN74HC138N. In fact, you could make a pretty cool interim project using only 8 displays.
Wow. Starting this type of project just 4 days before it is due is a pretty bold & risky move.
(I admire the ambition and naivete of youth)
Hopefully I can help steer you in the right direction.
astrog21:
The main issue is as to where to plug all of the wires in. It doesn’t specify how to connect the Real Time Clock, the SN74HC138N, or any of the AM/PM LEDs.
But you can figure out based on the information and code provided.
A couple of things you must understand.
Have a very close read of the description on the page you linked to.
Pay particular attention to the "NUMBERS PROBLEM" section about the issue of using the 9 Adafruit modules
(the part about needing 9 devices but the jumpers only allow 8 devices on the I2C bus)
Then you must understand that i2c is a BUS. Any device on the bus can be addressed.
The RTC uses i2c so it is just another device on the i2c bus.
The "i2c bus" is 4 signals. SDA, SCL, and power signals on the Arduino.
Real Time clock
It will be connected directly to the Arduino I2c bus pins since it is just an i2c device and nothing complicated/special is needed to talk to it.
SN74HC138N
See the web page you linked to. It has a picture of how it is wired up. The "NUMBERS PROBLEM" section has a part that talks about the issue of how to talk to 9 devices when you can only address 8 on the i2c bus. And there is a diagram of how the 138 is wired up to the LED backpacks to the i2c bus.
AM/PM leds
Look at the sketch code.
You will see in setup() the initialization of the AM/PM pins in a loop.
The key take away from that is the pin numbers being used (which tells you which Arduino pins are used)
and the state they are being set to LOW, along with the comment that says "off".
So now you know which pins to use and that HIGH turns them on and LOW turns them off.
So you wire the LEDS using your series resister between the Arduino pin and ground.
ArduinoPIN->resistor->LED Anode , LED Cathode->GND
NOTE: the parts list does not seem to mention any resistors but you MUST use them on the AM/PM LEDs just like driving any standard LED. And if you look at the picture of the components on the breadboad you can see them.
I'd use something like a 1k or 2k resistor. It must go in series with the LED to limit the current.
Value is not super critical but larger will make the led dimmer.
BTW, what is a "year 10 project"?
(2nd year of HighSchool?)
--- bill
Thanks for your help!
Over the weekend I will try and get it working. I will start by getting one display working, then building up from there.
Where do the 'select' wires in this diagram go to?
I'm from Australia, so the education system is a bit different. It's the 3rd last year of high school.
astrog21:
Where do the 'select' wires in this diagram go to?
When in doubt, refer to the code.
If you look in the setup() routine for the sketch you will see which Arduino pins they initialize for the 138 select pins.
They will connect directly to those Arduino pins.
Note that select/address line 2 (pin 3) of the 138, is grounded to ensure that the 138 only uses the lower two select/address lines.
--- bill
Hi Everyone,
I have managed to get everything working. I have removed the SN74HC138N and am now using two Arduino Uno’s. One of them reads the time from the Real Time Clock and then displays the present time across three displays.
The other Arduino is used to drive the static displays (Destination Time and Last Time Departed).
All of the connections are soldered and working perfectly. All I need to do now is to glue all of the components inside the aluminium case I milled at school.
Once that is done, I will post some pictures.
Thanks for all your help!
astrog21:
I have managed to get everything working. I have removed the SN74HC138N and am now using two Arduino Uno’s. One of them reads the time from the Real Time Clock and then displays the present time across three displays.The other Arduino is used to drive the static displays (Destination Time and Last Time Departed).
All of the connections are soldered and working perfectly. All I need to do now is to glue all of the components inside the aluminium case I milled at school.
Clearly you are a lot more competent than the fellows here took you for!
Actually, you could do it using software I2C with one Arduino module (Pro Mini) without the 74HC148 - the Adafruit people just chose to do it that way.
In fact, there is an even more clever - and simple - way; you use Arduino pins to change the address selections on the displays.
Hi,
Well done.
Two arduino's, good idea (Aussie Ingenuity), just I thought you only had the parts required(one controller).
And the hardware, aluminium case did not exist?
I'm pretty new to all of it.
How "pretty new"?
It looks like you actually read the advice given in building and how things work.
The problem that the forum sees is lots of enthusiasts who try a project that has been put on the net and are supposed to work.
However quite a few of them, and we see them here, the project has the DaVinci syndrome, something is left out or configured wrong, so the project doesn't function as it should.
Tom.....
Hi Everyone,
When I say ‘pretty new’, I meant that I have had little experience with Arduino. I have controlled some LEDs and motors, but that is about all.
The project is working perfectly, so I am not going to worry about trying to run it off of one Arduino for the moment, but thanks for the suggestion anyway. I chose to purchase a second Arduino to save me the headache of trying to work out the SN74HC138N.
I had purchased the hardware months in advance, but never really got around to playing with it.
I should have been more descriptive of what I had and didn’t have, as well as my experience at the start of the thread.
I just worked through the list by cattledog, and referenced that with the detailed information by bperrybap. I had one display working, then got the real time clock to display the time on it, then added more displays, then worked out how to address the displays and show the time across all of them.
The project has been on display in a school exhibition over the last couple of days. A lot of people seem to think that it is a bomb, but the people that recognise it love it.
Anyway, here is a picture:
Thank you to everyone for your help!
astrog21:
The project has been on display in a school exhibition over the last couple of days. A lot of people seem to think that it is a bomb, but the people that recognise it love it.
The problem is that the flux capacitor is missing.
Would be fascinated to know what exhibition that is.
Hi,
Good job...Yes we are all a bit bomb shy these days.
Tom....
Great Job on your project.
You are obviously talented and resourceful. Many of us on the forum try to encourage young people but are disheartened by the posters do not know how to ask a question or take advice. Your success certainly brightened my day.
Is your project related to Back to the Future Day?
Back to the Future Day refers to the date October 21st, 2015, which the characters Marty McFly and Doctor Emmett Brown travel to in the second installment of the Back to the Future trilogy
Wow. That is a great looking project.
I never really paid that much attention to the original prop in that they used 7 segment leds to spell out the month. So that means that had to travel in FEB, JUL, AUG, SEP, or OCT since you can't really spell the other months using all capital letters.....
I like your version better.
30 years ago this project would be MUCH more difficult as many of the components like microcontrollers simply didn't exist and the gcc tools didn't start to exist until the late 80's.
--- bill