Fair warning
So far, only one person I’ve told about this project thinks it’s a good idea. Everyone else looks at me wtih a mixture of pity and puzzlement, neither of which emotions seems to be mitigated by my explanation. Clearly, the best thing to do with the project is to bury it quietly, and where better to commit something to obscurity than on my blog?
A little bit of background
My eyesight is rubbish. With glasses on, I can see perfectly. Without them, I’m as blind as a bat. When I go to bed, I take off my glasses. If I wake up in the middle of the night, I am unable to find out what time it is without putting my glasses back on and looking at an illuminated clock. The problem is, that by the time I’ve done this (and waited for my ageing eyes to focus properly), I’m fully awake. If it turns out that it’s far too early to get up, it can take ages to get back to sleep.
The usual suggestions
Most people say “Can’t you get a clock with a big display?” It’s a logical suggestion, if you can see well. For me, the digits on a bedside clock would have to be about a foot tall for me to be able to read it without glasses. Others say “Can’t you turn on a light?”, but doing so brings me to full wakefulness (and runs the risk of disturbing my wife). Fools suggest “Can’t you just use an alarm clock?” I do. But if I wake up before it goes off, I want to know if it’s three hours before, or only one. If it’s only one, I’ll get up and do something useful.
The solution
Here it is, in all its glory:
No, it’s not the internet. It’s the Buzzclock. To use it, you press and hold the button on the top. It then tells you the current time by silently vibrating: one pulse for each hour, then one shorter pulse for each ten minutes past the hour. There is virtually no noise, no light and best of all no need to put on glasses. The time is not accurate to the minute, but it’s good enough to make the decision whether to get up or to go back to sleep.
Don’t laugh, it hurts my feelings.
Inside the box
It’s a bit of a squeeze. The brains of the device is an arduino Nano, connected to a battery-backed real time clock. The Nano is a very useful device – more or less the same functionality of an arduino Uno or Leonardo, but in a much smaller package. It’s also dirt cheap (about three of your earth pounds). You can plug it directly into a breadboard for prototyping, and then when you want to build the final device, you can solder it in to a PCB or stripboard, or you can plug it in to a terminal block breakout board, as I did.
The real time clock (RTC) module I used came from ebay, and also cost about £3. It uses a DS3231 chip, has a rechargeable backup battery and (unnecessarily) has 32k of flash memory on the same board. I guess the flash is there in case you want to use it for datalogging. The RTC chip also has a built in thermometer (I don’t know why).
The RTC and the arduino communicate over the two-wire I2C interface. This makes the wiring really simple. There are handy arduino libraries available to do all the heavy lifting. Thsi is a good thing, because the RTC chip has its own protocol for getting and setting the clock time, and the libraries wrap this into a nice simple set of commands.
The final component in the build is the vibration motor. This is one designed for mobile phones. As usual it’s from ebay and cost about a pound. This is a thing of beauty. It’s a small dc motor (it runs off 5V – the arduino can power it directly from an output pin) with an eccentric weight on its output shaft. When the motor spins, it vibrates. There is nothing special about that, except that it is tiny. The whole assembly is only about 10mm long. The engineering that goes in to mass producing those must be just staggering.
How it works
THe button is just a push-to close switch. As long as you hold it down, the arduino gets power. Let it go, and the power is cut. This way, the arduino uses no power at all when not in use. The RTC has its own backup battery, so it keeps track of time without using the main battery.
Every time you press the button, the arduino boots up. It then contacts the RTC to get the time from it, and sets its own clock. The output pin connected to the motor is brought high for half a second then low for half a second for each hour in the current time. After a full second pause, shorter pulses are used to indicate the tens of minutes after the hour. And that’s all it does. At four o’clock in the morning, when all is pitch black, its a very quick way of working out it’s too early to get up.
Setting the time
At the moment, you can only set the time by connecting the arduino to a PC and sending a string over the serial port. This is not a big deal, because the RTC keeps time over a long period. It’s only an issue when the clocks change to or from daylight saving time, and I can cope with the effort twice a year.