Wireless doorbell battery monitor

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We know exactly what [Dan] is going through. We also bought a cheap wireless doorbell and are plagued by the batteries running down. When that happens, the only way you know is when people start pounding on the door because you’re not answering the bell. Well no more for [Dan]. He built a backup system which monitors the voltage of the batteries on the chime unit.

You can see the small bit of protoboard he used to house the microcontroller and the UI. It’s an ATtiny13 along with a green LED and a single push button. The idea is to use the chip’s ADC to monitor the voltage level of the pair of batteries which power the chime. When it drops below 3V the green LED will come on.

First off, we wish these things would come with better power supply circuits. For instance, we just replaced the CR2032 in an Apple TV remote and measured the voltage at 2.7V. That remote and the chime both run from a 3V source. Can’t they be made to work down to 1.8V? But we digress.

In addition to monitoring voltage [Dan’s] rig also counts the number of times the chime has rung. Every eight seconds it flashes the count in binary, unless he presses the red button to clear the count. This is shown in the video after the break. We guess he wants to know how many times this thing can be used before running the batteries down.

Seriously though, for a rarely used item like this how hard would it be to use ambient light harvesting to help save the batteries? Looking at some indoor solar harvesting numbers shows it might be impossible to only power this from PV, but what if there was a super-cap which would be topped off with a trickle from the panels but would still use the batteries when that runs down?

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Viscerally pleasing electromechanical doorbell

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Sure, we could just slap the steam-punk label on this doorbell hack, but we think that cheapens it. The rig uses a combination of mercury switch and creative mechanics to form a doorbell. And we think it goes beyond aesthetics to a statement of who you are starting with the front door of your house. No wonder [Nick Normal] has moved it along with him from home to home over the years.

The portion to the right is the ringer itself. Pulling on the lever moves the chain through an eyelet to affect the mercury switch mounted above. That switch completes the circuit which drives the motor on the “bell” unit. We use quotes because instead of ringing a bell it’s striking the large valve control wheel which looks like it came straight from the same industrial plant where The Joker took his unfortunate fall into a vat of acid.

This certainly gives you something to aspire to. And if you think you’ve already achieved a doorbell setup on similarly-geeky footing why haven’t you tipped us off about it?

Playing a WAV file with 64 bytes of RAM

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[Jacques] thought his doorbell was too loud, so of course the first thing that came to mind was replacing the electronics and playing a WAV file of his choosing every time someone came knocking. What he ended up with is a very neat circuit: he used a six-pin microcontroller with 64 bytes of RAM to play an audio file. (French, Google translation)

The microcontroller in question is a PIC10F322. one of the tiniest PICs around with enough Flash for 512 instructions, 64 bytes of RAM, and a whole bunch of other features that shouldn’t fit into a package as small as a mote of dust. Without the space to store audio data on the microcontroller, [Jacques] turned to a 64 kilobyte I2C EEPROM. The PIC communicates with the EEPROM with just two pins, allowing it to read the audio data and spit it out again via PWM to an amplifier. The code required for this feat is only 253 instructions and uses just a few bytes of RAM; an impressive display of what a very small microcontroller can do.

Simple hack plays any sound as your door chime

[Jim’s] technique for turning a wireless doorbell into a custom ringtone player is so simple. He manages to get the entire thing done using only a screwdriver and wire clippers as tools. But if you’re looking to use this over the long-term we’d recommend soldering the connections rather than relying only on the twisted wires.

Above you can see all the components used in the project. The wireless doorbell unit is no different from most battery-operated units on the market today. Inside the Radio Shack box is a recording module that lets you play up to 20 seconds of audio. This is powered by the 9V battery on the right. [Jim] removes the speaker from the doorbell and clips off one of the wires that connected it to the board. This is reused as the ground connection for the recording module. The other speaker wire is connected to the ‘Play’ button on the module’s PCB. That’s it, just record your custom sound and pack everything back into the doorbell’s case. You can see the entire hack and hear a demonstration after the break.

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Janus: The Gatekeeper

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[Piet] wrote in to tell us about his hack that allows for his front gate to be opened without a key. Unlike this hack that we featured in August, you don’t need a subway pass, just a good memory. As explained in his article (and the video after the break) if the proper sequence of doorbell rings is input, the gate unlocks itself.

For hardware a [mehduino] is used to take the doorbell input and decide whether or not the “secret knock” has been achieved. The door can be unlocked remotely via a button on the processor. Reprogramming the code is achieved by simply holding the program button while the code is entered on the “remote ringer” button.

Be sure to check out the video after the break to see this lock in action. The housing application may not be exactly what you expect. Also of interest, is that in true hacker fashion, the bare processor is hanging by a hook on his wall! Continue reading “Janus: The Gatekeeper”

Doorbell to Internet bridge also useful for other home automation

This wireless doorbell hack can send a text message when someone rings. Adding the hardware to the chime unit turned out to be quite simple. It shows potential for a slew of other applications.

[Martin] started the project with a breakout board he had designed for an RFM12B wireless transceiver board. This board is popular because of its low-cost, small size, and ease of operation. [Martin’s] breakout is barely larger than the RFM module itself, and merely adds an ATtiny84 to the mix. In the case of this doorbell project he uses a pin interrupt to detect when the doorbell’s LED is illuminated. This wakes the chip from sleep and sends a message back to the receiver that something has happened.

The receiver can do anything it wants with that data. In this case it uses an email-to-SMS service to send [Martin] a text message. But the home automation applications are vast for this simple hardware. We have a water heater that is not near a floor drain so we use a simple leak detector to sound an alarm if there is ever a problem (the water heater sits in a shallow tray). That works if we’re home at the time. Using [Martin’s] solution could extend that alarm’s reach worldwide.

[via Hacked Gadgets]

Crystal doorbell helps class up the joint

Even if you live in a dump this quick build will make your doorbell sound high-class. The new rig uses a crystal goblet to alert you of guests at the door. We suppose the room-silencing sound of flatware on a wine glass does make a great attention getter.

For [Tobias] the hardest part of the build was getting his wife to sign off on it. But he says the 1970’s era original was looking pretty shabby, which kind of made his argument for him. It took just two hours to develop and install the replacement. It uses a servo motor with an articulated striker to ping the glass which is hanging inverted between two pegs. The original AC transformer (which are most often 16V) was used to power the Arduino. He built a simple rectifier along with a big smoothing capacitor to make sure the Arduino doesn’t reset when voltage dips. Although it’s not mentioned in his comments, we’d bet the doorbell wire has been rerouted to connect directly to the Arduino, rather than remain patched into the power loop.

Don’t miss the clip after the break to hear how great this thing really does sound.

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