Relay Computer Starts with an Adder that Makes a Racket

Computers built using discrete logic chips? Seen it. Computers from individual transistors? Impressive, but it’s been done. A computer built out of electromechanical relays? Bring on the ozone!

The aptly named [Clickity Clack]’s new YouTube channel promises to be very interesting if he can actually pull off a working computer using nothing but relays. But even if he doesn’t get beyond the three videos in the playlist already, the channel is definitely worth checking out. We’ve never seen a simpler, clearer explanation of binary logic, and [Clickity Clack]’s relay version of the basic logic gates is a great introduction to the concepts.

Using custom PCBs hosting banks of DPDT relays, he progresses from the basic AND and XOR gates to half adders and full adders, explaining how carry in and carry out works. Everything is modular, so four of his 4-bit adder cards eventually get together to form a 16-bit adder, which we assume will be used to build out a very noisy yet entertaining ALU. We’re looking forward to that and relay implementations of the flip-flops and other elements he’ll need for a full computer.

And pay no mind to our earlier dismissal of non-traditional computer projects. It’s worth checking out this discrete 7400 logic computer and this all-transistor build. They’re impressive too in their own way, if a bit quieter than [Clickety Clack]’s project.

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Remote-Operated Gate On A Budget

Sometimes, a simple fix is the best solution. Lacking extra funds for a proper remote-controlled gate-opener after the recent purchase of their farm, redditor [amaurer3210] built one as a birthday gift for his wife.

Supported on pillow block housings, a 10″ wheel is connected to the motor by via a 3D printed pulley and a timing belt turned inside-out to allow for slippage — in case of obstacles or manual opening of the gate. If you’ve ever worked with belts in your builds, [amaurer3210] adds that during sizing he uses a few layers of fiberglass tape as a stand-in for the belt to avoid frustration over final belt size and tension.
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A solar powered cattle crossing gate

solar-powered-cattle-crossing-gate

Anyone who’s traveled the grounds of a cattle ranch will tell you there’s a lot of stopping to open and close gates. But this project is aimed at letting you operate the gate from the comfort of your vehicle. It uses a spool of wire as the gate, lowering it for vehicle access with the use of a remote control.

The base station uses a solar panel to keep the battery topped off. But if you’re not frequently using the system it shouldn’t take much electricity at all. An Arduino board listens for the signal from the remote control. It then unspools the wire until it lays flat across the ground and can be driven over. Once the car has passed another click of the remote raises the gate back into position. There’s even a version that uses two gates which make up a cattle corridor.

We were thinking that it would be easy enough for the cows to push right through this. But after seeing the clip after the break it’s obvious they like to follow the rules.

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Arduino parking lot attendant

Here’s an automatic parking gate for toy cars. There’s no need to press a button, the electronics detect the presence of a vehicle on either side of the gate, raising it after verifying that the lot is not already full. It’s the same idea as counting how many people enter a room in order to switch the lights but the hardware is just a bit different.

The system is controlled by a pair of sensors in the paper which serves as the parking lot. There are three sheets of heavy stock, the top and bottom both have aluminum foil on them, with the center layer  as a separator. There are holes cut in the separator where the hash marks are seen above. By adding a little pressure to the car when you drive it up to the gate this completes a circuit instructing the Arduino that there’s a vehicle in position.

You can see a demonstration, as well as the guts of the build, in two videos after the break.

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Janus: The Gatekeeper

janus-001

[Piet] wrote in to tell us about his hack that allows for his front gate to be opened without a key. Unlike this hack that we featured in August, you don’t need a subway pass, just a good memory. As explained in his article (and the video after the break) if the proper sequence of doorbell rings is input, the gate unlocks itself.

For hardware a [mehduino] is used to take the doorbell input and decide whether or not the “secret knock” has been achieved. The door can be unlocked remotely via a button on the processor. Reprogramming the code is achieved by simply holding the program button while the code is entered on the “remote ringer” button.

Be sure to check out the video after the break to see this lock in action. The housing application may not be exactly what you expect. Also of interest, is that in true hacker fashion, the bare processor is hanging by a hook on his wall! Continue reading “Janus: The Gatekeeper”

Automatic speaker control via TV

[Jon] wanted his speakers to come on and off along with his TV. The speaker heats up if left on so he didn’t want to do that. But killing the power also resets the volume level (this is an old set of PC speakers and the remote is wired, not IR) so using one of those switched power strips was out as well. He thought a bit about trying to use the power LED on the TV to build his own circuit when it dawned on him. It’s possible to monitor the USB port on the TV and use it to switch on the speakers.

The circuit above uses a couple of opto-isolators to protect both the television and the speakers. The 5V line from the USB port on the back of the TV is monitored by an XNOR gate (which helps to filter out some of the toggling at power-on). When that gate latches it activates a 555 timer which in turn fires up the speakers. Presumable this happens when power is cut as well, but we’ll let you work through the circuit logic yourself.

Automated entry for a garden gate

[Dan McGrath] tipped us off about a solution for a problem that most people don’t have. He built a web-based entry system for his garden gate. This isn’t quite as original as that chain and sprocket dorm room system, but it does use a keypad for entry. [Dan’s] already got a web server and home automation box that is always running. He coded a webpage that presents a virtual keypad for code entry. If the right code is input the system unlocks the electronic strike on the other side of this gate. Since the interface is a web page you can load if from any web browser (an iPhone is used for demonstration purposes after the break). But if you don’t have internet access you’re in trouble; there’s no physical keypad. But we guess you could always just jump the fence.  Continue reading “Automated entry for a garden gate”