Water tank level meter prevents overflow

roof-water-tank-level-meter

Most of the homes in the area where [Raikut] lives have tanks on the roof to hold water. Each is filled from a well using a pump, with gravity serving as a way to pressurize the home’s water supply. The system isn’t automatic and requires the home owner to manually switch the pump on and off. [Raikut] made this process a lot easier by designing an LED bar indicator to monitor the water level.

The sensor is very simple. Each LED is basically its own circuit controlled by a transistor and a few resistors. A 5V signal is fed from 7805 linear regulator into the tank. The base of each transitor is connected to an insulated wire, each extending different depths in the tank. As the water rises it completes the circuit, illuminating the LED.

[Raikut] is conservation minded and built a buzzer circuit which is activated by the LED indicating the highest water level. If someone walks away from the pump switch while it’s filling the alarm will sound as it gets to the top and they can turn it off before it wastes water.

[via Reddit]

Bluetooth headset garage door opener update

bluetooth-headset-garagedoor-opener-update

[Lou Prado] sent in a link to his new video on using a Bluetooth headset as a garage door opener for your Android device. This isn’t a new hack, and we’ve actually seen him pull it off once before back in 2011. But we’re running this as an update for a couple of reasons. First off, we had forgotten about the hack and it’s worth revisiting. Secondly, the headset which he used with the initial hack has gone out of production. He chose a new model, and the assembly video (embedded after the break) which he made is a treasure trove of best practices to use when hacking consumer electronics.

Here’s how the hardware part of the hack goes. He removes the speaker from the headset and solders the base of a transistor in-line with a resistor to the red wire. The emitter connects to the grounded frame of the USB charging cable which is plugged into an outlet next to your garage door opener. The collector of the transistor is then connected to the garage door opener, along with a common ground connection, allowing audio from the headset to trigger the transistor to open the door.

The systems is secure based on Bluetooth pairing, which was done with his phone before starting the hardware hack.

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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]