Wiring up a lot of LED segment displays

One look at this display and you know there’s a whole lot of pins that need to be wired up. Now look at what those display modules are mounted on. That’s right, [Kemley] is using point-to-point soldering to rig up this big display. It sports four sixteen segment modules on top for alpha-numeric information, and eight large seven segment modules for displaying numbers only.

We’re not certain as to how the electronics are arranged. When talking about the 16-segment modules he mentions that all four are in parallel with NPN transistors to switch the common anode of each. That’s easy enough to understand. But when you get a look at the transistor board you’ll see 24 of them in use. He’s included a 150 ohm resistor on the collector of each transistor. It must be set up to only allow one segment of each group to switch on at a time? We’d guess that each segment is divided into two (upper and lower pins are multiplexed separately), which would explain the double set of transistors. As for date and time, an Arduino board monitors a DS1307 RTC and manages the scanning of the display.

Wristwatch measures your perception of time; also tells time

This wristwatch is hiding a lot of features in its hardware and its software. It’s called the TicTocTrac and it’s a Senior project for a pair of students at Cornell University. Judging from the sheer volume and quality of the project documentation we wonder if someone has a science writing career ahead of them? Be we digress… It’s a clock and we love it!

First off, this does more than just tell the time. In fact, that’s almost an ancillary function in this case. The wristwatch is more of a metering device to record your own time-based behaviors. Find yourself checking your watch frequently as the lunch break approaches? This watch records that activity and you can later graph the data. This allows you to analyze how you percieve the passage of time. The more often you check the time, the slower you feel time progressing. The documentation does a much better job of describing this than we have time for, so check it out.

On the hardware side of things we’re quite impressed. The housing is 3D printed. It hides two half-circle PCBs below the full-circle PCB face plate. The half-boards leave space for a tiny rechargeable battery, and host a vibrating motor and RTC chip. Instead of using buttons, there’s a piezo sensor which detects when you tap on the top of the watch.

Six-digit VFD alarm clock

[Haris Andrianakis] just finished building this very clean-looking vacuum fluorescent display clock. It shows six digits using IV-11 tubes, and also has a half-dozen RGB LEDs to spice things up (check out the video after the break for an example). An ATmega168 drives the device, controlling the display and serving as a battery-backed real-time clock.

As with any tube-based clock there’s a fair amount of work that goes into driving the display. Each tube has a filament which requires 1.2V, and the segments themselves need 60 volts to light up. The microcontroller is not hard to protect; this is done with a series of transistor-based circuits used for switching. But the need for three voltages (to power microcontroller, filament, and segments) means a more complex PSU design. [Haris] chose to use a MAX6921 to simplify the process.

If you’re considering building something like this, we’d recommend looking for some 12-segment tubes. As we’ve seen before, they can display letters as well as numbers in case you wish to repurpose the device in the future.

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Auto-locking pet door ensures that your outdoor kitty obeys its curfew


If you’ve got a pet that roams freely in and out of your house, you may find yourself wanting to more closely regulate how they come and go. [tareker] was looking to keep his cat indoors at night when dangerous animals might be lurking in the neighborhood, but he didn’t want it to become a hassle.

He already had locking pet door on hand, which he hacked to regulate the egress and ingress of his cat automatically. He installed a pair of reed switches to determine if the door had been opened outwards (cat leaving) or inwards (cat returning), keeping track of the state using an Arduino Nano. A servo motor attached to the door’s frame locks the door whenever it detects the cat is safely inside after nightfall.

While he also added an RGB LED to reflect the status of the door, he’s considering connecting it to the Internet so that he can control and check the door from wherever he might be at the moment.

Arduino aquarium lights

[Kalle Hyvönen] just finished building his own aquarium lights. He used four powerful soft-white LEDs, mounting them on a pair of heat sinks to keep things cool. Now he could have just connected them to the power supply and plugged it into the wall, but instead he included is own controller. An Arduino drives the switch-mode power supply, offering dimming thanks to PWM, and the ability to automatically switch the light on and off using an RTC chip with a battery backup. The sketch includes the ability to alter the lighting schedule and other variables by sending serial commands through a USB connection. This protocol is detailed with comments in his sketch.

We’ve seen a lot of interesting aquarium light projects. This one that uses heat from the LEDs to warm the water is one of our favorites. Others are full of features like this version that includes a moonlight mode. But Arduino enthusiasts don’t have to look far to find offerings like this PAR meter build, or this aquarium light controller library which can be recreated using the ubiquitous controller board.

Hacking an AC outlet timer for project use

[Karl] needed a programmable real-time clock for one of his projects. He considered adding an RTC chip, LCD screen, and some buttons for use with a microcontroller. That’s not necessarily hard, but it takes time and can be considered a project in itself. Instead, he headed to the hardware store to look for a cheap solution. He was able to get this AC outlet timer for a song. It’s got everything he needs; twenty programmable on/off events, a calendar to track time and day of week, and a user interface made up of a low-power LCD and four buttons. He cracked open the case and patched into the electronics for use with any project.

You can see the solder-tab battery in the middle of the board (green coin-cell). That actually runs the timer circuitry and display. It’s topped off when the unit is plugged into mains, but [Karl] ended up replacing it with a much higher capacity AA rechargeable battery. The device works just like a thermostat, using very little power and driving a relay at the appropriate time. Batteries in thermostats seem to last forever and we can expect the same performance from this device. [Karl] rerouted the trigger signal from the relay to his own 2N2222 transistor. This way the device can switch loads running at voltages other than its own 1.2V operating level.

Stock timers are great. They’re mass-produced which makes them cheap, and you can do some interesting stuff with them. We really enjoyed see this other mechanical version hacked for hydroponic use.

Very accurate clock can’t be read accurately

[Martijn] is showing off his new clock which he calls a Light Spectrum Clock. We like to look of it, using RGB LEDs in five squares that remind us of some of those LED coffee table builds. From left to right this shows the week, day, hour, minute, and second. Simple, right?

We had to smile a little bit when looking through his write up. He chose an Arduino nano as a controller, using a TLC5940 chip to drive the LEDs. But it is the inclusion of a DS1307 real-time clock that we find amusing. It will keep quite accurate time (not quite as well as the DS3232 but still respectable) but the fuzzy display technique makes telling the time accurately an impossibility. But like other color-based clocks, that’s part of the fun. The real reason for using an RTC chip is that they usually include battery-backed operation so that you can shut off the LEDs when you’re not around and the clock will continue to tick.

You can watch the seconds pass by as fading colors in the clip after the break.

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