A 555-Based, Two-Channel Remote Control Circuit

December 4, 2013 by Phillip Ryals 21 Comments

[fahadshihab], a young tinkerer, shared his circuit design for a simple remote control using 555 timers. Using a 555 calculator, he designed a clock circuit that would run at 11.99 Hz. Two transistors are connected to inputs (presumably button switches). One sends the plain clock signal, and one sends the inverted clock signal. A matching circuit at the other end will separate the channels. All it requires is connecting the two circuits in order to synchronize them. It would be easy enough to interface this with an oscillator, an IR LED, or a laser for long-range control.

The great thing about this circuit is its simplicity. It’s often so easy to throw a microcontroller into the mix, that we forget how effective a setup like this can be. It could also be a great starter circuit for a kid’s workshop, demonstrating basic circuits, timers, and even a NOT gate. Of course, it would be a good refresher for those without a lot of circuit knowledge too. Once you’ve mastered this, perhaps an AM transmitter is next?

Crafting A Liquid Crystal Display

December 2, 2013 by Brian Benchoff 17 Comments

Throughout the 1960s, the management at RCA thought LCD ~~displays~~ were too difficult to commercialize and sent their engineers and researchers involved in LCDs off into the hinterlands. After watching [Ben Krasnow]’s efforts to build a liquid crystal display, we can easily see why the suits thought what they did. It’s an amazing engineering feat.

Before building his own version of an LCD (seen above in action), he goes through the mechanics of how LCDs operate. Light enters the display, goes through a polarizer, and is twisted by a liquid crystal material. The first successful LCDs used two types of liquid crystals – chiral and nematic. By combining these two types of molecules in the right proportion, the display can ‘twist’ the polarized light exactly 90 degrees so it is blocked by the second piece of polarizing film in the display.

Besides getting the right crystals and engineering processes, another major hurdle for the development of LCDs ~~displays~~ is transparent electrically conductive traces. [Ben], along with every other LCD manufacturer, uses a thin layer of indium tin oxide, or ITO. By embedding these clear electrodes in the display, segments can be built up, like the seven segment displays of a calculator or a bunch of tiny dots as found in a TV or computer monitor.

In the end, [Ben] was able to build an extremely simple single-segment LCD ~~display~~ out of a pair of microscope slides. It does modulate light, just barely. With a lot of work it could be made in to a calculator type display but for now it’s an awesome demonstration of how LCDs actually work. Continue reading “Crafting A Liquid Crystal Display” →

The Atari Jaguar That Should Have Been

November 27, 2013 by Brian Benchoff 36 Comments

jag

Released in 1993, the Atari Jaguar suffered from a number of problems – it was difficult to program, had hardware idiosyncrasies, and with the CD drive was vastly overpriced compared to the Sega Saturn and Sony Playstation released one year later. Nevertheless, the Jaguar still has a rabid fanbase that counts [10p6] among them, and he’s created what Atari should have released 20 years ago.

In a few forum threads at jaguarsector (login required) and nexgam.de (no login, German), [10p6] goes over his changes to the classic Jaguar + CD combo. He’s stuffed everything inside a new case, cutting down on the amount of plastic from the old enclosure. A proper integrated power supply has been added, replacing the two power supplies used in the original. It’s also overclocked to 32 MHz, compared to the 26 MHz of the stock unit, making this a very powerful system that could have easily competed with the Saturn and Playstation.

[10p6] has an amazing piece of hardware on his hands here, and should he ever want to make a few molds of his new Jaguar, he could put together some sort of kit to replicate this build. He’s still working on finding a model maker and perfecting his case design, but a new, improved version of the Jaguar is something we’d love to see in a limited production.

Amateur Radio Transmits 1000 Miles On Voice Power

November 26, 2013 by Adam Fabio 50 Comments

Many of us tried the old “Two tin cans connected by a string” experiment as kids. [Michael Rainey, AA1TJ] never quite forgot it. Back in 2009, he built “El Silbo”, a ham radio transmitter powered entirely by his voice. El Silbo is a Double Side Band (DSB) transmitter for 75 meters. While voice is used to excite the transmitter, it doesn’t actually transmit voice. El Silbo is a CW affair, so you should bone up on your Morse Code a bit before building one. Like many QRP transmitters El Silbo’s circuit is rather simple. A junk box loudspeaker is installed at the bottom of the can to convert voice power to electrical power. The signal is passed through a step up transformer, and used to excite a 75m crystal. Two NPN transistors (in this case MPS6521) pass the signal on through a second transformer. The signal is then routed through an LC network to the antenna.

Back in 2009, [Michael] brought El Silbo to the Maine coast in an attempt to make a transatlantic contact. This isn’t as far-fetched as it sounds – [Michael] has “crossed the pond” on less power. While the attempt wasn’t successful, [Michael] has made connections as far as 1486km, or 923 miles. That’s quite a distance for simply yelling into a tin can! One of [Michael’s] favorite El Silbo stories is a 109KM conversation (QSO) he had with W1PID. [Michael] found that the signal was so good, he didn’t have to yell at all. He reduced power by dropping to his normal speaking voice for the “dits and dahs”. The two were able to converse for 17 minutes with [Michael] only using his speaking voice for power. We think this is an amazing achievement, and once more proof that you don’t need a multi-thousand dollar shack to make contacts as a ham.

Continue reading “Amateur Radio Transmits 1000 Miles On Voice Power” →

Mini Supergun PCB

November 25, 2013 by Brian Benchoff 18 Comments

A few decades ago, Japanese manufacturers of arcade games realized they should make a connector for all their boards that provides the power, controller, video, and audio I/O. This became the JAMMA standard and it make arcade owner’s lives awesome. Because you can buy arcade boards off the Internet, arcade enthusiasts figured out they could build their own console with an ATX power supply, AV connectors, and a few controllers. These ‘superguns’ as they’re called are big devices with wires all over the place. [Charlie] wanted to condense the size of his supergun and ended up creating a single PCB solution (link dead, try the Internet Archive version).

The JAMMA compatable boards require a few power connections; +5 V, +12 V, and -5 V. Of all the boards [Charlie] has collected so far, he realized only one used the negative supply. This, along with a big 12V laptop power supply, means the only power connection for this mini supergun is a single barrel connector.

For the controls and A/V, DSub and SCART connectors are commonplace. Laying these parts out in Eagle resulted in a single-sided board that is easily fabbed by etching with a toner transfer at home.

There are a few problems with the build, as [Charlie] admits. Some of the pins on the JAMMA connector aren’t on the board. These are only ground pins on the pinout, and so far everything works okay. It’s still a great project, though, that turns old arcade boards into a playable device with a minimal amount of hardware.

Commodore 64 Power Glove Is So Bad

November 14, 2013 by Brian Benchoff 11 Comments

The Nintendo Power Glove was terrible. Really, really terrible. Thanks to modern components, though, it’s possible to recreate the Power Glove experience in a way that doesn’t suck so much. That’s what [Leif] did with his motion sensing glove for the Commodore 64.

Instead of rolling his own IMU and putting it in a glove, [Leif] is using SonicWear SoMo, a glove originally designed to generate MIDI data for performance pieces. Inside this glove is a 9 DOF gyro/accelerometer/magnetometer, uC, battery, and XBee that can be easily reprogrammed to do something a little more (or less) useful than simply sending MIDI notes and commands.

[Leif] reprogrammed the XBees to use I/O line passing instead of sending serial data, and connected the recieving XBee to the C64 joystick port through a very simple circuit with a hex inverter.

All the code to turn a SonicWear glove into a C64 controller is available on the Github, and there’s a neat demo video of [Leif] demoing his glove at the VCF Midwest late last month.

Reverse Engineering The Z80’s 16-bit Increment/Decrement Circuit

November 11, 2013 by Adam Fabio 1 Comment

z80

Increment and decrement. They sound like simple functions. But even the simplest functions can get quite complex in a microprocessor design. Ken Shirriff has written up a great blog post about his reverse engineering of the Z80’s 16-bit increment/decrement circuit. The Zilog Z80 was one of the most popular microprocessors of the 70’s and 80’s. It was used in many classic computers such as the Osborne 1. These machines would often use the Z80 to run the popular CP/M operating system.

The increment/decrement circuit is responsible for updating the program counter register during normal (non branch) operations. The increment/decrement circuit also handles the stack pointer register during stack operations, as well as several other functions. One might wonder why a separate adder would be used when the microprocessor has a big ALU available to it. The answer is twofold. First the ALU is already in use handling user math operations. Secondly the increment/decrement circuit has to be fast. A generic ALU just won’t be fast enough.

One classic adding circuit is a Ripple Carry Adder. Ripple Carry Adders get the job done, but they are slow. Note slow is measured in nanoseconds here – there are no clocks involved in the circuit. The whole thing becomes a classic combinational logic optimization problem. Each layer of logic adds a gate delay to the circuit. As the carry has to ripple through all 16 bits, there are 16 gate delays before the final result is available at the outputs. Delays like these are what limits the maximum clock speed for a given circuit.

The Z80 uses some tricks in its increment/decrement circuit. The first is Carry-lookahead. A carry-lookahead circuit will calculate the carry values directly from the inputs. This reduces the gate delays significantly, but it requires more real estate on the die. A second trick is the carry-skip circuit. Carry-skip calculates the result for groups of bits rather than each bit individually. Again, it will reduce gate delays, at the cost of real estate. The actual Z80 implementation uses a mix of both circuits. Several other “helper” circuits are also used. Surprisingly the Z80 has specific logic just to check for 1 (0x0001) on the internal address bus. This circuit is used during memory move loops to inform other parts of the chip that a loop is about to complete.