Jonathan entered his illogical Dickson doubler into the Open 7400 Logic Competition. My entry demonstrates how you can use the internal protection diodes and back powering to power a 74HC14 at a voltage “double” (minus diode drops) that of the primary power supply. This method was tested on a 74HC14 and a 74HC595, but it […]
Category Archives: 7400 contest
7400 competition entry: The Computer
John’s second entry into the Open 7400 Logic competition is a working computer with serial I/O and a lights ‘n switches front panel. He built a 8bit CPU with a single accumulator, basic arithmetic (+,-,&,~,<<,>>), conditional branching and subroutines, as well as 1KB of RAM. After building and testing that it works, he unfortunately had […]
7400 competition entry: 7400-based USB prank
Arup entered his USB device not recognized design into the Open 7400 Logic Competition. It uses a logic chip to stimulate a USB host just enough to get a “Device not recognized” response from Windows. Once the prank succeeds a “1” is displayed on a 7 segment display. Via the forum.
7400 Contest: 24 hours left
Reminder to all those interested in entering their projects into our Open 7400 Logic Competition: Entries must be received by October 21, 2011, 6AM GMT. You only have 24 hours left to send your entry in. Entering Entries can be posted on in our forum, on your personal blog, or even a handy how-to site like Instructables. When you’re […]
7400 competition entry: CMOS digital clock
Giuseppe built his CMOS digital clock two years ago and decided to enter it into the Open 7400 Logic Competition. By using a 2Mhz quartz crystal and a 21bit counter he managed to make a 1Hz clock signal which drives his design. Implementing 2 binary counters programed to count to 60 he managed to get […]
7400 competition entry: Four digit RPN calculator
John entered his four digit RPN calculator into the Open 7400 Logic Competition. This is the fist of two entries he made while attending “Digital Hardware Lab” courses at the University of Utah. It is a 4 digit RPN calculator that can add and subtract, designed entirely out of logic ICs. The first few weeks […]
7400 competition entry: TV pattern generator
Ajoy built a TV pattern generator for the Open 7400 Logic competition. Using 74C14 Shmitt inverters to generate various timing signals, he later combines them using a few NAND 74C00 gates to get a B&W TV video signal generator by CCIR-B standards. A full write up explaining the operation of his circuit, along with the […]
7400 competition entry: Lights out game
Bertho entered his Lights out game into the Open 7400 Logic Competition. After working out the math behind lights out, Bertho decided to make his own using only logic chips. The object of the game is to turn the lights off by using a + shaped mask.The board automatically generates random patterns over a 5×5 […]
Open 7400 Logic Competition: Only two days left to enter!
Reminder to all those interested in entering their projects into our Open 7400 Logic Competition: You only have two days left to send your entry in. Entering Entries can be posted on in our forum, on your personal blog, or even a handy how-to site like Instructables. When you’re ready, please submit a link to […]
7400 competition entry: TTL Tilt Sensor
Chris added another entry to the Open 7400 Logic competition: TTL Tilt Sensor. His device works by converting accelerometer analog outputs into digital signals via 3×4 comparators, 6 are used for the X-axis and 6 for the Y-axis. From then on discrete logic chips are used to convert the different signals into various positions on […]
7400 competition entry: Hex KeyPad
Adam submitted his Open 7400 Logic competition entry, a 16 button keypad that outputs the hexadecimal value in a 4 bit binary equivalent. Adam wrote This is a handy device for prototyping, etc… It’s a hexadecimal keypad (0..9, A..F) that outputs the hexadecimal value on 4 digital binary lines (one nibble). It has both active […]
7400 competition entry: SPI LCD backpack
Stephen added his entry in the Open 7400 Logic competition, he made a LCD backpack that uses the SPI interface. Using two 74LS595 serial to parallel shift registers connected in series, he successfully sends data to the 16×2 LCD and adjusts the backlight brightness, by sending 2 bytes over the SPI. The first byte to be sent is displayed on the LCD, and […]
7400 competition entry: Analog comparator
Joseph built an analog comparator for the Open 7400 Logic competition. Using two NAND 3-input gates and a D-type flip-flop, he build a clocked analog comparator. After reviewing the internal composition of a CMOS NAND 3 gate he noticed that two of them connected in the right way make up a comparator. To make his own version he used a D-type flip-flop to […]
7400 competition entry: Animated LED Christmas sign
Raj entered his Animated LED Christmas sign into the Open 7400 Logic Competition. Having already build a PIC controlled version, he wanted to try and control the sign using discrete logic only. The individual letters are build from red LEDs and run of a 32V power supply. Check out the video of this project below. Via […]
7400 competition entry: Masochist’s video card
Chris entered his Masochist’s video card into the Open 7400 Logic Competition. Using only discrete logic his circuit cycles through 8 presettable colors at a variable frequency. Using a simple resistor network he outputs it over the VGA output. It is well documented and all the design files are available. Check out the video below. Via […]
Open 7400 Competition sponsors
Logos Electromechanical LLC The Gadget factory Thanks to the sponsors who made the Open 7400 Contest possible!
7400 competition entry: Money counter
Here’s an entry in the Open 7400 Logic competition: Money counter It’s a money counter based on pure 7400 logic and a bunch of 555. It can count 5 different types of coins. And it will show the current amount in the 7 segment displays. There are 3 files, two IEE papers (one for spanish […]
7400 competition entry: Discrete logic POV clock
Matt’s entry in the Open 7400 Logic competition: Discrete logic POV clock. This persistence-of-vision clock was built entirely out of discrete logic chips. The design consists of three boards, a LED array and a drive motor. The digit board keeps the time while the display board controls the LEDs. The digit board Every second, a pulse increments the […]
Open 7400 Logic Competition update: 3 weeks left
There’s 3 weeks left to enter the Open 7400 Logic Competition. Check out the 40 entries posted so far. The list of prizes is amazing, get your project in by October 21st for a chance at this great swag: $100 cash, 3 “Hack Packs” with a Bus Pirate, LCD adapter, probe cable, and jumper wires, […]
7400 competition entry: Discrete servo driver
Here’s an entry in the Open 7400 Logic competition: Discrete servo driver. This entry is designed to control RC hobby servos. 8bit parallel BCD code input from a dip switch sets a pulse width between 0-25.6ms (180 degrees of motion). However on most servos the first 50 and the last 10 positions are unavailable so you have […]