An 840 Segment Display

A while back, [limpfish] bought a few four-digit seven-segment displays from a seller on eBay. A month or two later, thirty displays ended up in [limpfish]’s mailbox. Instead of using the one or two displays he thought he ordered, [limpfish] decided to do something very cool with these bits of seven-segment displays. He’s controlling all of them at once.

[limpfish]’s usual method of controlling a lot of LEDs is the MAX7219 LED driver. This chip can easily — and cheaply — control eight common cathode seven segment displays. There’s a problem with this plan, though: the LEDs received from eBay are common anode. That’s actually not a problem, because with a little effort and even more thinking [limpfish] got these displays to work with the MAX7219 driver chip.

With chips in hand, [limpfish] designed a small breakout board for the MAX7219 and two common anode 4×7 segment displays. These displays can be daisy chained, and connecting them all together results in a very weird but very cool visualization.

[limpfish] is treating this display as a bitmap display, which means it’s demo time. You can check out a 1337 01d skool demo playing on this 840-segment display in the video below.

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Father and Son Fix a Scale

It’s awesome when you can tag-team with your dad to fix stuff around the house. [Ilias Giechaskiel], with help from his dad, did a complete refurbishing of a broken bathroom weighing scale, but not before trying to fix it first. The voltage regulator looked bust. Powering the rest of the circuit directly didn’t seem to work, and none of the passives looked suspect. Most of the chips had their markings scratched off and the COB obviously couldn’t be replaced anyway.

Instead of reverse engineering the LCD display, they decided to retain just the sensor and the switches, and replace everything else. The ATtiny85 seemed to have enough IO pins to do the job. But the strain-gauge based load cell, connected in a bridge configuration, did not have a signal span large enough to be measured using the 10 bit ADC on the ATtiny. Instead, they decided to use the HX711 (PDF) – a 24 bit ADC with selectable gain, specifically meant for use in weighing scales. Using a library written for the HX711 allowed interfacing it to the Arduino easy. The display was built using a 4 digit 7 segment display driven by the MAX7219. A slightly modified LEDcontrol library made it easy to hook up the display to the ATtiny. The circuit was assembled on a prototyping board so that it could be plugged in to another Arduino for programming.

Since they were running out of pins, they had to pull out a trick to use a single pin from the ATtiny to act as clock for the display driver and the ADC chip. Implementing the power-on and auto-off feature needed another interesting analog circuit block. Dad did the assembly of the circuit on a prototype board. In hindsight, the lack of IO pins on the ATtiny limited the features they could implement, so the duo are planning to put in an Arduino Nano to improve the hack. If you’re ever stuck with a broken scale, he’s made the schematic (PNG) and code available for use.

8×8 LED Arrays Make for one Creepy Animated Pumpkin

[Michal Janyst] wrote in to tell us about a little project he made for his nephew in preparation for Halloween – a jack-o-lantern with facial expressions.

Pumpkin Eyes uses two MAX7219 LED arrays, an Arduino nano, and a USB power supply. Yeah, it’s pretty simple — but after watching the video you’ll probably want to make one too. It’s just so cute! Or creepy. We can’t decide. He’s also thrown up the code on GitHub for those interested.

Of course, if you want a bit more of an advanced project you could make a Tetris jack-o-lantern, featuring a whopping 8×16 array of LEDs embedded directly into the pumpkin… or if you’re a Halloween purist and believe electronics have no place in a pumpkin, the least you could do is make your jack-o-lantern breath fire.

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THP Entry: Tinusaur AVR Platform Teaches Noobs, Plays Game of Life

tinusaur[Neven Boyanov] says there’s nothing special about Tinusaur, the bite-sized platform for learning and teaching the joys of programming AVRs. But if you’re dying to gain a deeper understanding of your Arduino or are looking to teach someone else the basics, you may disagree with that assessment.

Tinusaur is easy to assemble and contains only the components necessary for ATTiny13/25/45/85 operation (the kit comes with an ’85). [Neven] saved space and memory by forgoing USB voltage regulator. An optional button cell mount and jumper are included in the kit.

[Neven] is selling boards and kits through the Tinusaur site, or you can get the board from a few 3rd party vendors. His site has some projects and useful guides for assembling and driving your Tinusaur. He recently programmed it to play Conway’s Game of Life on an 8×8 LED matrix. If you’re looking for the zero-entry side of the AVR swimming pool, you can program it from the Arduino IDE. Be warned, though; they aren’t fully compatible.

SpaceWrencherThe project featured in this post is an entry in The Hackaday Prize. Build something awesome and win a trip to space or hundreds of other prizes.

Controlling High Voltage 7-Segment Displays


The MAX7219 is one of those parts in your bin that has a “done and done” attitude. In case you’re unfamiliar, this chip can be used to control 7-Segment displays, 8×8 Matrix displays, or even a pile of random LEDs. You talk to it via a simple serial interface and it handles the tasks you don’t want to fuss with, such as multiplexing and modulation. Not all displays are alike, however, so [Raj] wrote in to show how he used the MAX7219 to control high voltage 7-segment displays.

The spec on the MAX7219 only allows an input voltage of 5V, which limits the driver output to around 4V and can cause problems when using large displays that series-connect LEDs internally. [Raj’s] solution allows the MAX7219 to control displays with combined forward voltages of up to 24V, and as an added bonus, the circuit maintains compatibility with existing microcontroller libraries. We imagine this could be a nifty trick to keep on hand the next time you need to control large scoreboard displays.

The circuit works with the help of intermediate drivers to essentially level-shift the voltage to the display, which both provides the high voltage and protects the MAX7219’s inputs. One of the drawbacks of this circuit is losing the MAX7219’s constant current feature, requiring that each segment connection includes a current-limiting resistor. We appreciate this design’s attention to default states, because you wouldn’t want all of your LEDs turning ON during boot-up!

Prototyping a modular LED matrix


[Will] was toying with the idea of creating a scrolling LED marquee to display messages as his wedding in May. But you’ve got to crawl before you can walk so he decided to see what he could do with the MAX7219 LED driver chips. They do come in a DIP package, but the 24-pin 0.1″ pitch chip will end up being larger than the 8×8 LED modules he wanted to use. So he opted to go with a surface mount part and spun a PCB which makes the LEDs modular.

These drivers are great when you’re dealing with a lot of LEDs (like the motorcycle helmet of many blinking colors). Since they use SPI for communications it’s possible to chain the chips with a minimum of connections. [Will] designed his board to have a male header on one side and a female socket on the other. Not only does it make aligning and connecting each block simple, but it allows you to change your mind at any time about  which microcontroller to use to command them. For his first set of tests he plugged the male header into a breadboard and drove it with an Arduino. We hope to hear back from him with an update when gets the final device assembled in time for the big day.

Incredible fabrication process makes this Word Clock stand out

From the look of it his is just another Word Clock, right? From the outside maybe. But if you take a look at the build photos this a good example of extreme fabrication.The design uses a five-layer lamination of glass bezel, vinyl lettering, diffuser, mounting plate, and back panel. The mounting and lettering layers were labor intensive, but are also the reason for the gorgeous finished look.

The bezel consists of black adhesive foil applied to the back of the glass faceplate. The letters were cut out using a vinyl cutter, and the lamination process happened in a pool of water. This technique helps to ensure that no fine particles end up between the glass and the foil.

The wooden mounting bracket was ordered from a local kitchen cabinet fabricator. It’s MDF that is 17.7″ and has been edge wrapped in glossy white PVC. Once it arrived, [Muris] started drilling the 248 holes and their counter sinks. This is on the front side of the layer and when sprayed with silver paint the countsinks act as reflectors. On the back side he milled groves to accept PCB strips to host the LEDs as well as the breakout boards that hold the MAX7219 drivers.

Don’t miss the video clip after the break that shows off the final product.

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