[Bozar88] lives in an apartment building that has a buzzer at the front security door. Guests find your name on the panel next to that door, and press a button to ring the phone just inside the entry of each apartment unit. He decided to extend the built-in capabilities by adding a morse-code entry password which unlocks the security entrance automatically (translated).
He designed a circuit and etched his own board which fits nicely inside of the wall-mounted phone. It uses an ATtiny2313 to implement the coding functions. The device attaches to the intercom line in order to detect incoming button presses from the entry panel. There’s some protection here to keep the signal at or below 5V. The output is two-fold. The microcontroller can drive the microphone line using a transistor, which gives the user audio feedback when the code is entered. To unlock the door an opt-isolated triac (all in one package) makes the connection to actuate the electronic strike on the entry door.
The video after the break is not in English, but it’s still quite easy to understand what is being demonstrated.
Continue reading “Apartment entry morse-code lock”
On his blog, [Kenneth Finnegan] recently showed off a replica of a fun toy he used to play with as a kid, a telephone intercom system. The setup is pretty simple, requiring little more than a pair of analog phones, a battery, and a resistor.
The phones are connected to one another using a standard telephone cable, but [Kenneth] uses a 9v battery to introduce a small bias current into the loop, allowing the speakers at either end to hear one another. He also added a small LED into the circuit so that there is a visual indication as to when both handsets are off hook.
The setup is very simple at the moment, though [Kenneth] does have some ideas in mind to enhance his intercom system. He hopes to tweak the remote phone to ring when the local phone is picked up, among other things.
Telephone technology is nothing new, but for just a few dollars (or less) your kids can be entertained for hours as [Kenneth] was way back when.
Continue reading to see a short video overview of the phone system, and be sure to share your ideas for enhancing it in the comments section.
Continue reading “This toy intercom system is way better than a pair of tin cans and some string”