[John Zitterkopf] is in the middle of restoring a vintage Sega Star Trek Captain’s Chair arcade game for the upcoming 2012 Texas Pinball festival, though one prerequisite for the show is that the game supports some sort of free play mode. At this point he doesn’t have the option of tracking down a freeplay ROM for the device, so he had to come up with a solution of his own.

He did not want to alter the machine’s operation in any significant manner, and this meant preserving the functionality of the coin chutes. To do this, he put together a small circuit that uses a pair of cascaded 555 timers to provide the machine with the proper signaling to simulate coin insertion, while still accepting coins. You might initially think that this could be easily accomplished by shorting a pair of contacts in the coin chutes, but as [John] explains, the process is a tad more complex than that.

If you have some old arcade games kicking around and are looking for a non-invasive way to make them free to play, be sure to check out his site for schematics and a complete BoM.

[M. Eric Carr] came up with an interesting build for the 555 contest earlier this year, and we’re pretty sure that it would have kicked the winner of the complex category off the throne if it were completed. Although it’s a few months late, we’re happy to feature at least part of his 555-based computer on Hack A Day.

[M. Eric Carr] started off implementing Boolean logic with a 555. After building a universal gate, he moved onto putting one bit of memory in a single 555. This design uses the 555 as a latch and is one of the craziest off-spec uses of a 555. While fitting 24 bits of memory on 5 large bread boards may seem like a waste, it’s a far cry from the square feet or acres of other computer builds we’ve seen.

From the post on the 555-based memory, [M. Eric Carr] says a completed design of his computer could be up and working this summer. It’s already August, so we’re hoping he’s still working on his design. Check out the video of the memory below.

[TBJ] is building what he calls a junkbox 3D printer. You can probably guess that he’s trying to salvage most of the parts for the device, and after pulling a stepper motor from an old printer he was in need of a way to control it. What he came up with is a stepper driver that uses discrete components that are easy to acquire and inexpensive. The design calls for two inputs, one that toggles the direction in which the motor will spin, and the other that triggers one step of the motor. A CD4013 dual flip-flop takes care of both of these inputs in one chip package.

The motor is driven by a pair of H-bridges that he built using six transistors each. The trick with a stepper motor is that you need to drive the four poles of the motor to a specific logic level at a specific time. For this [TBJ] uses a CD4017 decade counter. A network of diodes grounds half of the output lines based on the flip-flop that controls direction. Our friend the 555 timer provides a clock for the circuit, keeping everything moving at a predefined rate. Check out the video after the break for an explanation and demonstration.

The team at Evil Mad Scientist Laboratories needed a footstool. Obviously not content with buying one, they came across the idea of building a 555 footstool.

After finding some dimension drawings of the 555 timer IC, the team scaled everything up 30 times. While a normal DIP-8 555 is around 0.4 inches long, the footstool is over a foot long and eight inches high. The stool was cut on a CNC mill out of 1/2″ plywood, glued together, and finally panted with the correct date code and the logo of Evil Mad Scientist Labs. The finished product is amazing. We’ve been looking for a nice table, and the idea of an 8 foot long wooden 64-pin Motorola 68000 is pretty appealing.

While there’s no electronics in the footstool, it’s not hard to imagine fabricating some aluminum pins and a hollow body so a huge, functional 555 could be built. It would be possible to use discreet components following the block diagram of the 555 to build a huge Atari Punk Console; the gigantic capacitors are fairly easy to build in any event.

After having his mints disappear for quite some time [Quinn Dunki] came up with an idea to get back a the fresh-breath thieves. A bit of circuit design, parts scavenging, and free-form construction led to the creation of his mint-tin burglar system.

Here’s how it works. Flip the on/off switch in the base of the mint tin before you head off for lunch or a coffee break. When the foul-mouthed pilferer hits up your stash they’ll get what they were looking for at first. But by opening the tin they tripped a timer circuit that will send the mints vibrating across the table soon after having been opened.

The breadboard above holds the prototype timer circuit, built around or friend the 555 timer. The vibration motor from a cellphone is a perfect choice for this hack as it’s very small and is just waiting to run from a low-voltage source. We especially liked the use of the cells from inside a 9V battery as a power source and the compact assembly that manages to fit inside the mint container.

[Fede.tft] wrote in to tell us about some work he’s been doing to save battery life for LED dominoes. He originally got the idea after reading this post about the electronic gaming pieces. That project was aimed at the 555 timer contest and therefore, used a 555 timer. [Fede.tft] calculates the battery life for the CR2302 battery in the 555 circuit at no more than about 80 days. That’s if you never use them and the LEDs are never illuminated. It makes sense to remove the batteries from the device when not in use, but a redesign to increase efficiency is definitely worth the effort.

This rendition does away with the 555 chip in favor of a CMOS chip. By building a circuit around four NAND gates of a CD4011 chip, the standby lifetime of the battery is calculated to increase to about 4.5 years. Not bad! Add to this the fact that replacing the 555 timer didn’t increase the component count, the price for the chip is similar to the 555, and you didn’t need to resort to a microcontroller. Yep, we like it.

Bring communications jamming technology into your TV viewing experience by building this infrared LED driver circuit. You’re probably familiar with the TV-B-Gone, which let’s you turn off any television at the touch of a button. But what if you actually want to watch the program that’s currently on the screen when the person with remote-in-hand doesn’t? That’s where this little marvel comes in.

[KipKay's] IR jammer uses a 555 timer to constantly transmit infrared traffic. The signals it’s sending out don’t correspond to commands the TV (or any other IR remote-controlled device) will respond to. But if the light intensity is strong enough, they will interfere with any signals coming in from a remote or even from a TV-B-Gone. [KipKay] wisely hides this circuit inside of another remote control so that the other couch potatoes you are thwarting won’t get wise to what’s happening. If they want to watch something else they’ll have to get up and walk over to the entertainment center to do something about it, and what’s the chance that’s going to happen?

Don’t miss [KipKay's] infomercial-esque presentation of this gadget after the break.

Freedombot is a neat little robot designed for exploring magnetic surfaces. It has two whiskers for detecting objects in its path and two rare earth magnets which allow it to stick to your fridge.

Overall Freedombot may not be anything revolutionary but its builder [skater_j10] does a good job of covering topics which my be interesting to robotics beginners. For example he goes through the process of modifying some HiTec HS- 55 Micro Servos for continuous rotation which allows them to act as the wheels. To control the bot he uses two 555 timers wired up in astable mode to generate the needed PWM for the servos. The proximity sensors are simple limit switches with some wire soldered on to the end.  The end result is a neat little robot for roaming the front of your fridge. See a video of it in action after the break.

This happens to be [skater_j10]‘s entry into the 555 timer contest. Unfortunately the deadline has passed for new entries but be sure to swing by and check out some more awesome 555 hacking.

[dev_dsp] wanted to try his hand at creating a purely analog implementation of multiple synchronizing fireflies powered by a single battery and built from off-the shelf, through-hole components on inexpensive protoboard. In theory, even your local Radio Shack should still carry all of this stuff. He was obviously inspired by [alex]‘s fireflies that we’ve covered in the past, but he wanted to see how far it could be taken without the use of a microprocessor.

In the end, [dev_dsp] relied on one crucial piece of digital ware, the ever-popular 555 timer IC, but he’s using analog discrete components to do the grunt work of adjusting the phase of each firefly by feeding a little extra current to the trigger capacitor whenever the flash of a nearby firefly is detected. After the jump, you’ll find schematics and a video demo of three ASync-Firefly modules in various stages of assembly playing with one another while [dev_dsp] discusses their operation.

Inspired by the memory of a childhood electronics kit, [Frank] decided to make a new 555 Synthesizer and enter it into the 555 contest. [Frank's] remake is played with a stylus, and sports an attack and release envelope circuit, housed in a quick but effective acrylic case.

Using a single 555 timer, a hand full of capacitors, two transistors, and a healthy dose of resistors and potentiometers, the sound is quite impressive thanks to optional filtering, enveloping, and a lot of fine tuning. Full schematics, bill of materials, formulas, and board files are all available along with sources for some of the more specialized potentiometers.

Join us after the break for a ~13 minute long video, which is pretty cool, as it shows the device from prototype, and does some fast forward action though to the final product pictured above, though if you just want a demo of the 555 synth fast forward to 10:44

[R-B] designed a 555 timer circuit to scan a keypad. Keypads are common interfaces for small projects and require row and column scanning by a microcontroller. [R-B's] setup allows you to reduce the number of pins used on the microcontroller to just two. One is an interrupt that is triggered when any of the buttons are pushed, the other reads the frequency from the 555 chip. Each button has its own resistance which alters the frequency of the 555. The microcontroller reads the frequency for 100ms using a timer. The number of timer overflows that occur during that period directly correspond to the button press (five overflows for the numeral 5, zero overflows for the numeral zero).

We usually debounce our button presses for 40 ms, this is more than twice that amount of time but still not a staggering difference. It does make us wonder if you will miss quick button presses? The only really way to know is to try this out yourself. Check out the video after the break and don’t forget to leave a comment with your own experiences in working with the circuit.

[Roteno's] submission for the 555 timer design contest is an Internet connected earthquake alert system. It monitors the USGS website for earthquake data and plays a tune when an earthquake occurs. The data is available as a feed in the form of a TXT file which is pretty easy to parse using cURL. He chose an LPCXpresso board (which is an ARM development platform that can run a Linux kernel) along with an XPORT module to handle the Ethernet traffic.

So where does the 555 timer see some action? It is responsible for playing the tone when an earthquake is detected. But playing just one pitch isn’t much fun. Instead, [Roteno] built the circuit above which creates a resistor network switched by a series of transistors. This way he can use GPIO from the microcontroller to choose different pitches. Check out the video after the break to hear the results. At power-up all eight pitches are played as a test, and the alert sound varies in pitch and tempo based on the magnitude of the earthquake.

This 2-bit adder was a lot of work to build. It uses a total of thirty-six 555 timers and it does have the option of adding or subtracting numbers. It’s a rather unorthodox use of the part, depending more on the chip as an inverter and taking advantage of the fact that there’s an NPN transistor built into it. [cpu86] did use some PNP transistors to give him the ability to turn off some of the 555′s to get everything working correctly.

He explains the use of two’s complement in the subtracting feature but the process is just touched on very quickly. Luckily there’s a huge eagle schematic available with his project writeup so that you can follow along and really grasp how this thing works. We’ve generated a PNG and embedded it after the break for your convenience. You’ll find it just after the two videos of the device in action.

Adding:

Subtracting:

Schematic:

[Thanks Paul]

Everyone’s getting on board with the 555 timer projects. But [Tom] didn’t just come up with one project, he shared a slew of ideas related to analog robotics. They’re center around servo motor control. You can see in the video after the break he has a pleasing way of sharing a lot of details while also making an easy to view demonstration video. He’ll put up a schematic for about one second and then move on, saving those that don’t care about the details by not droning on.

The first schematic that flashes by is the main circuit for controlling the servo motor. The rest of the concepts build from this circuit, using light, sound, flex, and other sensors as inputs. For instance, the setup above is using a light sensor. When the ball blocks the light the servo moves that vertical rod hitting it out of the way. When it swings back the process repeats. It’s striking how lifelike the reactions are, reminding us of insect movements. But this is really just the tip of the iceberg as he’s got a lot of future video ideas that we can’t wait to see.

[Thanks Jeri]

[Apexys] is performing some experiments with switched-mode power supplies and needed to compare the inductance of the coils he was using. His multimeter doesn’t have an inductance testing function, but he does have a 555 timer on hand. He put the 555 and some other parts together to create his own L meter. The writeup includes the theory behind this meter, with an incoming AC source converted to a voltage by an RC network.

Once he’d worked out the design it was time to build the circuit. Instead of printing a circuit board he created what he calls a DCB; Drawn Circuit Board. We’ve got to admit that this was way faster than using toner transfer or soldering point-to-point. We also like his use of an Erlenmeyer flask and a torch to heat the etchant. We don’t make PCBs in the winter because our Cupric Chloride is too cold to use outside but that may change now. The final piece in the puzzle is an analog meter which he pulled from an extra microamp meter he had on hand. Check out the demo after the break.