This device helps you not lose your keys!
If you're like me then when you get home from work you immediately lose your keys after unlocking your door and you wait until the next day right before you have to leave to look for them. Yeah you may have a key hook or a bowl to put them in but there isn't a reminder to do so and that is where keyminder comes in!
Keyminder is a device that detects when your door opens and sounds an alarm and the only way to silence the alarm is to plug your key into the device via a 1/4 inch male jack thats on your keyring. Thus making you put your keys up so you know where they are for tomorrow!
Step 1: Watch the Video
Watch the video and continuing reading :)
Step 2: The Schematic and How It Works!
The keyminder is a simple device consisting of a circuit made up of a few transistors, resistors, switches and a decade counter. You can achieve what the keyminder does a number of different ways but I used what I had on hand to cut cost.
The counter has 10 outputs and a clock input as well as other connections. We are using 2 of those outputs. The outputs are triggered high one after the other based on a clock input signal. When the clock input goes high it causes the output of the counter to shift to the next in order. On one of the outputs we have a green led that acts as a standby or alarm inactive led, this lets us know that the alarm isn't triggered. On the other output we have the alarm triggering circuit that consists of a transistor that grounds the alarm and makes the speaker go off when activated. I'm using a hacked door alarm but you can use a piezo speaker instead. In order to silence the alarm you must pull the base of a PNP transistor high by closing it to vcc using the 1/4 inch male jack thats on your key ring. The jack acts as a switch and pulls the base high. Once the base is high no current flows through the PNP transistor to the alarm circuit, thus silencing it. The male DC jack has two pins and they are shorted together so it acts as a switch. Click on the schematic to view some notes I added!
The clock signal is generated based on the reed switch. A reed switch is a switch that opens and closes based on the proximity of a magnet. The magnet will be mounted on the door and the reed switch near it so when the door opens it pulls the magnet away from the reed switch causing the switch to open which then cuts the flow of current to a PNP transistors base off which allows current to flow through the transistor to the clock input of the 4017 decade counter. So when you open the door it acts as a clock input for the 4017 and triggers the output change. I added a button in parallel with the reed switch just in case you needed to reset the outputs or if you have a family member that wants to deactivate the alarm when they leave. But it's up to you not to use this button instead of plugging your key in.
Step 3: Soldering the Circuit
Take some time to consider the layout of your parts and solder it up according to the schematic.
Then mount it on your wall near a door and have some fun not losing your keys! Thanks so much for reading my ible! I will see you next time :)