Introduction: Safety Alarm Clock
I often find getting out of bed in the morning a bit tricky. When i have somewhere to be at a certain time, i get up pretty reliable. However when I want to get up it always seems that I manage to turn off my alarm clock before fully waking up.
Put it on the other side of the room? Multiple alarms? Sooner or later I acclimatise, and fall back to old habits...
This instructable will hopefully show you how to put your alarm under lock and key! This is the safety alarm clock.
Step 1: Things You Need
The chart below, I think does justice to the battle between my sensible conscious mind who wants to get up and do stuff and the selfish sleepy one who only wants to lie in bed.
The main point of my alarm hack was only to allow control of the alarm clock to me once the critical time had passed, once the sensible me was in control... I want the selfish sleepy me to be locked out of any alarm turning off privileges!
Things you will need
Cheapo digital alarm clock Get one with a back up battery if you want to do steps 6-8
Screwdriver to open alarm clock
Wire ( double insulated core and jumper)
SPST Key switch (available from maplins for �3 in the UK!!!!)
for making the clock unpluggable you will need
a 2N3904 transistor
buzzer (6 - 12V)
got all these? no? doesn't matter, the only thing you really need for this is the key switch and alarm clock the rest I'm sure you can improvise!
Step 2: Open Up Your Alarm Clock
Before you open the sucker up, find out the specifics to control the alarm. For instance on my clock the alarm would not go off when the snooze was depressed, would be reset by the alarm set button etc... Try to figure out a way to the control the alarm on and off with a only a single switch.
WARNING : This may be a mains operated device, make sure you unplug it from the wall before even looking at a screwdriver!!! To be extra safe, leave it overnight uplugged to let capacitors discharge etc...
Looking inside it should be a tangled mess of wires, circuit boards and other such electrical jetsam. Don't be scared because most of that stuff is not important.
Now you need to find access points to the various buttons and switches that control you alarm. You want to try and figure a way of using one and only one switch to turn the alarm on or off.
Step 3: Wiring
For my clock I saw that all of the buttons that had any influence on the alarm shared a common ground! If your clock is based on any sort of microprocessor, this will probably also be the case. Even if the relevan buttons are far apart, you may be able to find a common ground point for them.
you can use a multimeter which has a continuity mode to test if two points on the circuit are connected. Or if no continuity mode, measure resistance, low resistance (ie zero) means a connection.
Step 4: Modifications
The solution for me was to put the key switch (more on this later) in series on the common ground, I would also lam the switch on the side so that it was stuck on the alarm on position. to make sure that the alarm was not on every day, I shorted the button for the snooze.
This means that with the key switch open the alarm will go off, and only connecting the common ground with the key switch turns it off.
Step 5: Key Switch
I had seen these key switches in maplins a few months ago and thought I must try to get them into a project. A SPST cost only 3 pounds!!! It is basically an isolated switch that can only be changed by inserting and turning the correct key. A SPST switch has two positions, connected and unconnected.
Drill some appropriate holes in a project box or other container to house the key switch. If your alarm clock has enough dead space, you mount the switch on the body. Mine didn't, so i had to mount as a peripheral.
add another hole to your alarm clock to thread out the wire from the common ground, adding a knot before you leave, to make sure no stress is put on the connections themselves.
Thread the wire into your project box (adding another knot) and hook it up to the solder pots on the switch. I added some super glue to the bolt, key chassis, project box connection to make it extra sturdy.
Step 6: Unplugging
The clock still has a weak point. When you unplug it, the alarm dies... I wanted a way to remedy this situation without resorting to dangerously fixing the plug in the wall...
Now this clock has a back up battery which preserves the clock settings when it is unplugged. I broke out my multimeter to measure the current coming from the battery when the clock is plugged in and unplugged.
A small 0.3mA current when plugged in, and a large 2.3mA current when unplugged. I wonder if i could use that change in current to switch another componant?
Step 7: Transistorise
Transistors are great at controlling a large current by a small current. In this case I will use an NPN transistor to allow current to pass to a buzzer when the clock is unplugged.
Under normal conditions the current drawn by the clock is insufficient to allow any current to flow C to E and so the buzzer is silent.
When 2.3mA is drawn by the clock, the circuit is effectively opened between C and E, and so the buzzer can sound!
Step 8: More Wiring
Wiring up the schematic in the previous page was a little tricky... since it was all inside the clock.
I used crocodile clips whenever i was soldering the leads of the transistor. they can be pretty sensitive to heat, and the crocodile clip serves as a heat sink safety net for you.
I wrapped all the exposed joints with electrical tape and cut an extra slot around the rim of the clock so that the buzzer could go outside. If there is spare real estate inside your clock you can leave it inside, there wasn't in mine...)
If you hold the transistor with the flat face towards you, the leads from left to right are emitter, base and collector.
If you want to check that everything has worked before putting it together, be cafeful. Plugging and unplugging whilst the case is open is potentially lethal. don't touch anything inside if you plug in the clock.
Step 9: Put It All Together!
Hopefully everything should go back together nice and snug.
Set the alarm, turn the lights out, chuck the key somewhere in the dark and fall asleep confident in the knowledge that the time you set on the alarm will be the time the you get up!