An article I wrote for Electronic Products.
Having a key ring stuffed in your pocket isn’t the most pleasant shape. They can be sharp, bulky, and you’re always checking to make sure it’s there. But like the watches, cameras, and CD players before them, key rings are on their way to being gobbled up by mobile phones.
Thanks to ShareKey, the Android mobile app, leaving the house and worrying about your keys is a thing of the past.
ShareKey communicates with smartlocks on the door via NFC (near field communication), which allows wireless data to be exchanged across a small range. This system allows any smartphone to be accessible to the house, but only for a specified amount of time. Instead of making extra keys, the dog walker can be granted access to the house for an hour, and house guests can have access for days, or even weeks. Better yet, making copies of your electronic keys is quick. All it takes is a text or an email to the recipient’s smartphone.
ShareKey isn’t like UniKey and Lockitron, which send instructions via Wi-Fi and Bluetooth. It’s simple and secure, requiring a phone to be waved in front of the lock, making it difficult for hackers to intercept the signal.
Though it’s an Android app, there’s no reason why ShareKey couldn’t be ported to an iOS app, as long as Apple gives the next iPhone an NFC chip. The ShareKey system is not yet mainstream, but keyless door lock hardware is available for $150-200 per lock.
Having a hard time calculating RC frequency?
Electronic Products’ RC filter cutoff frequency calculator can help you out.
Simply put your values into the resistance and capacitor form boxes and hit the “calculate” button to find the cut-off frequency.
The simple R-C filter rolls off the frequency response at 6 dB per octave above the cutoff frequency. The position of the resistor and capacitor are switched to change from low pass to high pass, but the same calculation applies to both filters.
This calculator assumes a low source impedance, which is usually small enough not to change the corner frequency.
Calculating RC frequency has never been easier.