About this project
The Tempus Fugit is a simple WordClock interface board for your Raspberry Pi Zero or Arduino Nano. The time in words is spelt out on an 8 by 8 letter matrix, with accuracy maintained using an on-board battery backed real time clock chip.
Although the base WordClock will be the English language version pictured I will also include templates and s/w [via GitHub] for a Dutch and Latin version - See the Kickstarter updates more information.
Interested, but having trouble getting a Pi Zero - then start with a Arduino Nano. It is easy to change this out later on, just unplug the Nano and plug in your Pi Zero. You can also use the Tempus Fugit with any of the other Raspberry Pi computers - there is more detail on this in the following section.
The clock started out as a Christmas project for a Pi Zero I had just received. Having got a lot attention from my original blog post, I decided to work it up to launch as a Kickstarter, essentially to fund a production run of PCB boards. While working the PCB layout for the TF I realised it would be quite easy to incorporate the option to run the clock from an Arduino Nano. So spent a bit of time breadboarding it to check there were no problems with the Arduino RTC and display driver libraries, then added a Arduino Nano as an alternative processor option onto the PCB layout.
Finally in the spirit of flexibility I added extra drilling's so you can, with relative ease also mount a Raspberry Pi A / B onto the back of the TF board and then wire them it in using individual jumpers. The only Pi's I haven't catered for are the very early revisions without any fixing points. These will still drive the board but you will have to figure out your own mounting arrangements.
The guess is that most people wanting to support the Kickstarter will opt for the kit reward level, but I have included 2 additional 'ready built' levels - one which is PiZero ready and one which will include a pre-programmed Arduino Nano clone. The numbers are limited so please don't wait too long to pledge if interested.
The Tempus Fugit word clock displays the time using the '12 hour' format in words spelt out on an 8 by 8 letter matrix, time is displayed in 5 minute slots [5,10,15,20 ...]. The correct time is maintained when the unit is not powered by an on-board battery backed RTC chip.
With an 8 x 8 matrix there obviously have to be some compromises, for instance 'HALF' and 'TWO';
Even with the limits of an 8x8 matrix you can display time to a + / - 3 minute accuracy.
Three rear mounted pushes allow the time to set and adjusted as needed. Instructions will also be included on how to optionally set the TF time via a connected PC.
In normal operation the TF does not need to be connected to the internet or a host computer.
Pledge reward levels include kit an built versions of the clock, For an example of the detail that will be included in the instructions for the kit version follow this link to the Pi-LCD build instructions, my last Kickstarter.
The finished printed circuit board size will be about 112mm x 70mm, it could have been little shorter but with these dimensions the length to width ratio works out to 1.6 which is often referred to a 'Golden Triangle' - considered by many artists and architects to be the most aesthetically pleasing form of a rectangle, so I decided to stick with it.
With the exception of the display and Pi Zero / Arduino most other components are mounted on the rear of the board, - Pi / Arduino could have gone on the back but why hide a thing of beauty !
- Display - 60x60mm red
- No surface mount parts on the TF board, so should not be challenging to solder with a basic level of competence
- Raspberry Pi interface, compatible with old and new Pi's as it only uses the first 26 GPIO header lines
- Power for the board is via Pi's micro USB connector or for the Arduino it's Mini-B USB connector [note connecting leads and PSU are not supplied with any of the pledge options]
- The real time clock (RTC) is battery backed with CR1220 coil cell, [because of postage restrictions the battery is not included in any of the pledge rewards]
- There are 3 monetary switches, these are used to allow the clock to be set and to shut the Pi down cleanly when not connected to a host computer
The Letter Matrix
To keep costs down I am NOT planning to commission a custom acrylic overlay, to date I have found laser printed squares to work fine, this also gives you the opportunity to experiment with different fonts. I will include a few pre-printed overlays in the kits as well as providing templates on-line.
Addtionally overlays for the Dutch and Latin versions will be included with the pledge rewards
- Python code will be available for down load via GitHub for Raspberry Pi setup and as a sketch for the Arduino
Differences between prototype and final production version
- Slightly smaller [112/70mm]
- The 3 pushes will be rear mounted and changed to low profile parts
- Most components with the exception of the Pi / Arduino will be rear mounted
- Sockets will be included in the kits to give the option not to solder the Arduino / Pi Zero directly in - with the PiZero I think it is actually easier to solder it directly as you only need to solder GPIO lines used not all 40 !
- The RTC will be incorporated directly onto the PCB rather than as separate daughter board
- The power on indicator LED will not be included as both the Pi and Nano have on-board power indicators
Current Design Development Status
The design is at the working prototype PCB stage, as you can see from the main project picture, the work todate and remaining design activities are detailed in the following bullet points
What’s been accomplished so far
- The hardware design is complete
- I have identified multiple sources for all the parts
- Pi and Nano hardware has been prototyped on breadboards and tested
- The PCB layout is complete and tested
- The software for the Raspberry Pi version has been running on the prototype for over a month now, but I will tidy it up a little mainly to improve the commenting. The Arduino software still needs some work but I have tested all the functional blocks together. Currently I am using less than 30% of the Ardunio's memory this will grow slightly but I do not envisage any capacity issues
- Proto-type Dutch and Latin version are up and running
What work remains to be done
I have now received and tested the prototype PCBs against a Rapsberry Pi boards and Nano Clones. This has allowed me to check the layout and importantly confirm the mechanical interfaces are correct. I am will be going through a second prototype cycle which is allowed for in the overall reward delivery plan.
From the software perspective there is no no significant development work to do so I plan to wait until the prototype boards are available and then complete the software.
One of the aims of the Kickstarter is to be able to offer the Tempus Fugit WordClock as a sensibly priced kit for schools and electronics clubs. This could range from a basic kit build to learn/improve soldering skills, to providing pupils with a ready build card without a processor and then asking them to research and select a suitable processor card. This would be a good example of applying an abstraction process to a real world problem [part of the UK key stage 3 curriculum].
One point I took away from a recent chat with a teacher is offering part built boards, to make the kits more accessible to children / adults with more limited soldering skills. This is something I certainly plan to do with the TF and my previous Kickstarter's.
- Pi Zero's and SD cards are not included in any of the pledge reward levels - not required if you are going down the Arduino route
- A PSU adapter is not included in any of the pledge rewards, I generally run the prototype with the official Pi PSU, but any PSU rated to work with a Raspberry Pi should be fine. For the Arduino option you will need an Adapter with a Mini-B USB connector or you can connect directly to the board check the Arduino website for details
- No case or mounting is included in the pledge rewards but I do hope to make a 3D printing file and some other options available at a later date
- Tools and solder needed to construct the kits are not included
- Pledge rewards will be sent out by Royal Mail using an untracked service - to keep postage costs down. The exception to this will be the built and tested boards will be sent tracked and / or signed depending on services available to your location.
Risks and challenges
The first point to make is that this is my 3rd Kickstarter, the first 2 were delivered to schedule, so I am confidant that my timescales are achievable.
The biggest risk is time impact from other work commitments, but I have additional help I can turn to if needed and have also limited the pledge numbers of the ready built boards to keep things manageable.
In terms of component sourcing all the parts are available from a range of suppliers. The one part I would not like to change is the LED matrix display so will probably forward buy an initial batch of these as soon as I hit the funding target. PCBs will come from European supplier again to minimise delay risks.
There is always the risk of finding unexpected errors on the PCB so although I am planning for a single prototype to keep costs down, I have included enough time in the schedule for a second prototype if needed.
The one this I cannot influence is availability of Pi Zero's, which is in part is why I extended the design to work with the Arduino Nano and as the Nano will be socketed there is no reason you could not start with a Nano then change this out for PiZero at a later date. You will also be able to rear mount all but the earliest Pi B's & A's to back of the board.Learn about accountability on Kickstarter
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