How computers work, starting with transistor gates

[Andrew Gibiansky] has just started a tutorial series called Computing with Transistors. It’s purpose is to pull back the many veiled layers between high level languages and the controlling of electrons. And fittingly this first post starts off by explaining voltage source, load, and current. Don’t be thrown by its simplicity though. [Andrew] quickly moves on to talk about switching transistors and how they are used to build gates like the OR NOR gate seen above.

If this is the least bit interesting you should also look back at the post about Nand 2 Tetris. It’s an online course that works its way through The Elements of Computing Systems text book. We’ve been following that journey ourselves, having made it through the hardware build in about a week. The assembler took about the same amount of time, and right now we’re in debugging hell trying to get the last function call and return parts of the VM translator to work right. We’ve used most of the skills needed in this journey before, but never all in one project. It really has shed a lot of light on the gaps in our knowledge, and we’re having a lot of fun at the same time!

[via Reddit]

Robot servo control using smartphone audio jack

[Jim] has an old Android phone he’d like to use as a Robot brain. It’s got a lot of the things you’d want in a robot platform; WiFi, Bluetooth, a camera, an accelerometer, etc. But he needed some way to make the mobile, mobile. What he came up with is a chassis with servos that can be controlled by the phone’s audio port.

To start his adventure he crafted a square wave audio file in Audacity and then played it back on the Android music player. By monitoring the output on an oscilloscope he found the wave was well produced, with peaks of about 1V. With that in mind he designed a circuit using two transistors to amplify the signal, thereby creating a usable input for the servo motors. Each motor has one of these circuits connected to it, with the left and right channels from the audio jack driving them separately. In the clip after the break you can see he even wrote a simple Android app to extend the idea to a more usable level.

This is a similar technique as used by the recon robot we saw about a year ago.

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Junkyard scavenging nets a tachometer to play with

We never thought to hit the automotive junkyard to find electronics we could play with. But [Istimat] was able to pull this working tachometer from an otherwise destroyed motorcycle dashboard. The Kawasaki part has just three pins on the back of it. By connecting 12V to the IGN pin, ground to GND, and tapping a 12V wire on the unlabeled pin he was able to make the needle dance and knew he was getting somewhere.

His microcontroller of choice for the project is an Arduino board. But the 5V logic levels aren’t going to put out the square wave needed to drive the device. A search of the internet led him to a 2-transistor circuit which lets him get the results seen in the video. His plan is to add functionality that uses the Arduino to pull data in from just about any source and display it on the dial. That computer desk that featured all the CPU load readouts immediately comes to mind.

Do you think the square wave circuit is more complicated than necessary? Could this be done with just one NPN transistor and a pair of resistors?

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Raspberry Pi controlled tank goes deeper than you might think

This remote control tank now takes its orders from a Raspberry Pi board. Well, actually it’s taking orders from commands pushed to the RPi board via SSH. The control scheme works out quite well. Using a low-profile WiFi dongle the RPi automatically connects to the wireless network when it is powered on. This makes it a snap to SSH into the device, and a more user-friendly controller will put a nice front-end into play at some time in the future.

But the real meat and potatoes of the hack comes in getting the RPi to talk to the tank’s circuitry. Just getting the Heng Long Tiger I remote control tank apart proved to be a ton of work as the treads need to be removed to do so and there’s a lot of screws holding it together. Instead of just replacing all of the control circuitry [Ian] wanted to patch into the original controller. To do so he spent a bit of time analyzing the signals with an oscilloscope and discovered that commands were coming in a Manchester encoded format. He established what various packets were doing, used a transistor to protect the GPIO pin on his board, and now has full control of the Tank. The final part of the hardware alteration was to power the RPi from the Tank’s battery.

After the break you can catch a demo of the reassembled tank sporting its new wireless controller.

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A DSLR shutter cable for Android

Here’s a very easy way to trigger your DSLR camera using an Android device. It’s a similar method used with IR triggered cameras, in that all you need to do is assemble some simple hardware to plug into the headphone jack. The app that triggers the camera simply plays back a well crafted audio file to do so. The thing that this cable adds is the ability to use the focus feature, since the cable has two data lines.

The hardware is dead-simple. A pair of NPN transistors and a pair of resistors are hosted by this small chunk of strip board. The audio jack for Android uses left and right audio channels to drive the base of these transistors. On the camera side of things the transistors are pulling the focus, and shutter contacts to ground. Once this is covered with shrink tubing it’ll be pretty rugged, and ready to be thrown in your camera bag for use on short notice.

[Thanks Hannes]

Building a computer with discrete transistors

You’re going to want to do some stretching before undertaking a soldering project like this one. We’re betting that the physical toll of assembling this 4-bit discrete processor project is starting to drive [SV3ORA] just a bit crazy. This small piece of electronic real estate is playing host to 62 transistors so far, and he’s not done yet.

It’s one thing to build some logic gates in Minecraft (and then turn then into a huge 16-bit ALU). But it’s another thing to actually commit to a physical build. [SV3ORA] does a great job of showing the scope of the project by posting a tight shot of one inverter, then three in a row, then the entire 8-bit address and display system. These gates are built on the copper side of the board, with the power feed, LEDs for displays, and jumpers for control on the opposite side. We’re excited to see where he goes with this project!

But hey, if you don’t want to do that much soldering there’s a lot you can do on a few breadboards.

Using diodes and transistors as solar cells

When you get down to it, solar cells aren’t much different from the diodes and transistors in your parts drawers or inside your beloved electronics. They’re both made of silicon or some other semiconductor, and surprisingly can produce electricity in the presence of light. Here’s two semiconductors-as-solar panel projects that rolled into the tip line over the past few days.

[Steven Dufresne] cut open a 2N3055 power transistor to expose the semiconductor material to light. In full sunlight, he was able to produce 500 millivolts and 5.5 milliamps. In other words, he’d need around 5000 of these transistors wired up to turn on a compact fluorescent light bulb. A small calculator has a much lower power requirement, so after opening up five transistors he was able to make a solar-powered calculator with a handful of transistors.

[Sarang] was studying solar cells and realized a standard silicon diode is very similar; both are p-n junctions and the only real difference is the surface area. He connected a 1N4148 to a multimeter and to his surprise it worked. [Sarang] is able to get about 150 millivolts out of his diode with the help of a magnifying glass. While he doubts his diode is more efficient than a normal solar cell, he thinks it could be useful in low-cost, low power applications. We’re thinking this might be useful as a high-intensity light detector for a solar cooker or similar.

After the break, you can check out the videos [Steven] and [Sarang] put up demonstrating their solar cells.

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