The Seven-Segment Display That’s Also An Input Device

November 5, 2022 by Dan Maloney 1 Comment

We’re used to seeing all manner of seven-segment displays, be they mechanical, electronic, or something in between. But what all these displays have in common is that they’re, you know, displays. Using them as inputs would just be crazy talk, right?

Perhaps, but we like where [Dave Ehnebuske] is going with “InSlide,” the seven-segment input device. The idea for this comes from the “DigiTag” display, which we covered back in October, and divides a standard seven-segment character into three vertical strips — two skinny ones for the outside vertical segments, and one wide strip holding the horizontal elements. By sliding these strips up and down relative to each other, the standard nine digits, plus a few other characters, can be composed.

[Dave]’s take on this theme started by building his display from laser-cut plywood pieces, which is a nice choice because of the good contrast between the white wood and the engraver segments. Next, he embedded rare earth magnets in the slides and installed seven Hall effect sensors in the frame. The sensors are connected to an Arduino Nano via a 74HC165 parallel-load shift register, which lets multiple modules be daisy-chained together. He also built an Arduino library to read the current state of the segments; it supports the full hexadecimal character set, or even duodecimal if you like.

[Dave] has shared the library, and it looks like you can get the build files for the mechanism from the original project. That’s good, because this looks ripe for hacking. It looks like it would be pretty easy to motorize a display like this by adding rack-and-pinion gearing and steppers — something like that could make an interesting clock.

Reading Inputs From Shift Registers Using Just One Single Pin

November 23, 2011 by Mike Szczys 11 Comments

Here’s an interesting article about reading data from shift registers using less than three pins. 74HC165 shift registers are a popular choice for adding inputs to a microcontroller. They have a parallel input register which can be read using the latch, then shifted into a microcontroller via the data and clock pins. For those counting, that’s the three pins normally associated with driving these devices.

This hack first does away with the latch pin. The addition of a carefully trimmed RC circuit (capacitor is charged by the clock pin, then the resistor lets that cap slowly discharge) means that the device will not latch until after the clock stops toggling. This technique drops the control down to just two pins (data and clock). You can still use hardware SPI to read the data using this method. It’s the same as using SPI to drive 595 shift registers except the microcontroller reads data instead of writing it.

But wait, there’s more! The diagram above actually shows a way of reading this shift register with just one pin. Notice that the clock and data pins are now connected to just one of the microcontroller pins. The data pin has an added resistor, which keeps the current low enough that it will not compete with the clock signal coming from the microcontroller. In between clock pulses, the microcontroller switches from output to input to read the data pin on each cycle. Give it a try, it’s a fun experiment!

Chipophone Plays Video Game Classics

July 22, 2010 by Mike Szczys 24 Comments

This thrift shop organ gets a new life as an 8-bit music maker. Called the Chipophone, it relies on an ATmega88 to produce sounds that you might associate with classic video gaming. [Linus Akesson] takes us through all of the different sound settings in the video after the break, including performances of your theme music favorites.

The original organ uses transistor logic making it rather easy to patch into the hardware. Thanks to the build log we know that [Linus] used 74HC165 input latches to monitor each of the switches for the 120 inputs. Fifteen of these latches work like a backwards shift register 74HC595, cascading all of the parallel inputs into one serial signal. From there the microcontroller takes over, monitoring the keys, pedals, switches, and potentiometers and outputting the appropriate sounds.

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