Building a combination lock with logic chips

The component gods must have smiled on [Darrell], because he recently ran into a cabinet full of 7400-series logic chips for sale at his local college surplus. All the regulars were there – flip-flops, logic gates, and SRAMs – in DIP packages. the 7400-series of logic chips gets very esoteric as the numbers increased, so when [Darrell] found a 74ALS679 address comparator, he didn’t quite realize what he had. After a quick review of the relevant datasheet he had a fairly good idea of the actual function of this chip and decided to make a combination lock.

From the datasheet, [Darrell] figured out how this small logic chip can compare two 12-bit addresses with only 20 pins: each of the 12 address pins are hardwired to match a single four-bit value. If the four-bit ‘key’ is set to 0110, the first six address pins are tied low, and pins 7-12 are tied high. After wiring up his address comparator to a trio of Hex dip switches, [Darrell] had a combination lock that used the word ‘FAB’ as a key.

In the 7400-series of logic chips, there are some oddballs; the 7447 seven-segment display driver is useful, but the 74881 ALU and 74361 bubble memory timing generator aren’t exactly something you would find in a random component stash. If you’ve got a weird logic chip build (there’s a 300-baud modem, you know), send it on in. You can check out an animated gif of [Darrell]’s lock after the break.

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Bending a printer control board to output POV messages

Confronted with the issue of finding a use for his mounting pile of junk electronics, [Rue] set out to build a persistence of vision device using a hardware state machine. We have a suspicion that his original link may go down if there’s too much traffic so here’s a cached link just in case.

Any board that is MSC-51 or MCS-48 based would have worked for his purposes. This is because the addressing scheme of the hardware makes it an easy hack. The image above shows him cutting off the processor from this board. It was chosen because of a 74HC373; it was a mistake at first but since it’s pin compatible with the 74HC374 that he needed a simple swap did the trick. From there a clock source was added, and the address information necessary to display the message was burned into an EEPROM.

Step twelve of his writeup shows a Morse Code message created by attaching the board to a broomstick and twirling it around in an arc. We took  just a minute to decode the message and believe it’s a shout-out to Hackaday. Nice, thanks for reading [Rue]!

Toy car fitted with lights and sirens is a children’s delight

police_car_lights_and_sirens

[Nathan], a member of the DangerousPrototypes forums, was looking for a project he could use to enter the 7400 logic competition they are holding. His kids had a small ride on police car, but the light bar on top contained no lights, and the car made no sounds when his children were in pursuit of baddies around the house. [Nathan] had all the inspiration he needed, and took to his workshop in order to fix this glaring oversight by the toys’ creators.

He designed a circuit based loosely around a Cylon-style light that he saw a while back at the Evil Mad Scientist Labs, which employed an oscillator and a 4107 decade counter to control the lights. His design uses a 74HC04 hex inverter as the oscillator, while the decade counter is used to modulate the siren’s frequency and control the rotating LED beacons.

The final result is great if you ask us. An “unnamed adult female” in the house was not nearly as impressed by the additions based upon how much time [Nathan] spent on the project, but his children were absolutely thrilled.

Continue reading to see a quick video of the revamped police car in action.

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7400 drum machine is a delight

[74hc595] just finished his entry in the 7400 logic contest. It’s a drum machine built entirely from 7400-series logic chips. He hasn’t quite reached full completion of the project yet. The hardware works just fine, and he’s built a foam core face plate with many more controls than you see here but much of the circuit is still on a breadboard at this point and only two of the channels have been complete thus far.

Jump to the video clip after the break to get the details of how the system works and to hear it in action. This demonstration is one of the best we’ve seen for a synthesizer project as he actually talks about what each control does, and how that is accomplished with the hardware. We’re not going to go into detail about the circuitry he’s designed. As we said before, it uses 7400 logic but also sources a 555 timer to keep the beat. The page linked above has a PDF of the schematic available and you could really lose a lot of time studying how he did this. We might even try to build it in a simulator to see what we can learn.

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Illogical voltage double uses logic

[Jonathan Thomson] just finished writing up his entry for the 7400 logic contest. It’s a voltage doubler that uses a 74HC14 logic chip. Because this is not at all what the chip was meant for–and he’s a sucker for puns–he’s calling it the Illogical Dickson Doubler.

What he’s got here is basically a charge pump built from a set of diodes and capacitors. On the breadboard you see two chips, one is used as a clock signal generator for the other which is acting as part of the charge pump. We’ve seen a string of hacks that misuse the protection diodes on the inputs of logic chips. In fact, [Jonathan’s] setup uses the same back power concept that barebones PIC RFID tag did. You may remember in that project the chip was being powered from one of the I/O pins, with the VCC pin not connected to anything.

We’ve embedded a video after the break with shows some voltage measurements, as well as an LED being powered from the doubling circuit.

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Rear window LED display gives other drivers a piece of your mind

rear_window_led_matrix

[Gagandeep] was sick and tired of discourteous drivers on the highway, so he decided that he would put together a display to let them know what he thought of their poor driving skills. He planned on putting the display up in the rear window of his car, so he had to ensure that it did not obstruct his view while driving.

He decided that an LED matrix would be the best way for displaying images and text while on the go, so he got busy constructing a 40×16 mesh grid for his rear window. Using a wooden template to get the spacing and positioning just right, he spent several days soldering the 600+ LEDs to one another. He used 74HC595 shift registers to manage the LEDs in groups of 5 columns, while an ATmega AT89C51 was tasked with generating the text and images to be displayed. All of the ICs were deadbugged in place, helping achieve [Gagandeep’s] desire of keeping his view unobstructed.

While we’re not well-versed on the legality of such a display, it looks great when animated. There are plenty of pictures of the grid in various stages of construction as well as videos of it in action in his Picasa album, so be sure to check them out. If you are looking for code or Eagle files, you can find those here.

Hackaday Links: October 16, 2011

Spinning DNA animation using sprites

[James Bowman] shows a way to use sprites to simulate parts of DNA moving in 3 dimensional space. The animations are driven by an Arduino board and Maple board, which allows a comparison of the processing differences between the two. [Thanks Andrew]

Tiny Pong

This Pong game is so small (translated), you’ll be fighting over who gets a closer view of the screen.

More CNC halftone pieces

[Christian] made a bunch of halftone pictures with a CNC mill. He took the concept from [Metalfusion’s] halftone projects and ran with it. He even posted some video of the machining process (turn down your sound before viewing this one).

Most useless machine

[Jumbleview’s] take on the most useless machine makes the entire lid shut off this rocker switch, instead of using a separate arm for the task.

7400 rectifier

[Noel] is using a couple of 7400 chips in an unorthodox way to form a full-wave rectifier. They’re not powered, but instead used for the internal diodes. It’s his entry in the 7400 contest.