Author Archives: DP

7400 competition entry: AM radio transmitter

Andrew entered an AM radio transmitter into the Open 7400 Logic Competition: My 7400 contest entry is an AM Radio Transmitter, which nicely complements another entry. The TX frequency is digitally tunable from 520kHz – 1.6MHz, although this part of the circuit is open loop, so tuning to a specific frequency may require a slight […]

7400 competition entry: Beeping down counter

Chris decided to enter another project into the Open 7400 Logic Competition. The beeping down counter, as it’s name suggests, is a pre-settable timer which beeps and uses a display to show the seconds left on the timer. The goal of this project is to duplicate the down counting circuit used by the character Ivan […]

7400 competition entry: FM modulation and demodulation system

Alifred and his friend entered a FM modulation, demodulation and transmission system into the Open 7400 Logic Competition. An input waveform enters the Voltage Controlled Oscillator (VCO), resulting in a FM modulated waveform. This is then sent to an IR LED (through a buffering MOSFET) and is received by a photo-transistor at the other end. […]

7400 competition entry: Discrete logic amplifier

Haley0918 added another entry to the Open 7400 Logic competition:  Discrete logic amplifier: This is my second entry for the 7400 logic competition. It’s a discrete logic amplifier made of mostly discrete logic chips. This amplifier is a continuation of my previous discrete logic preamp. The main objective here is to amplify the input signal […]

7400 competition entry: Digital die (74XX Family)

Sean Breen entered his Digital die (74XX Family) into the Open 7400 Logic Competition: Here is a rather simple but practical use for digital electronics…..dice! (or in the case a single die) Unlike many of the kits found online this one does not use a micro controller. The entire circuit is based around 74LSxx logic […]

7400 competition entry: TTL based range finder

Udif entered the TTL based range finder into the Open 7400 Logic Competition. It uses an ultrasonic sensor to determine the distance to an object. The sensor outputs a pulse, the width of the pulse is proportionate to the distance measured. The sensor signal drives a clock which in return increments a counter. The clock […]

7400 competition entry: TimeBonder 275

Sigitronic built the TimeBonder 275 and entered it into the Open 7400 Logic Competition. It is a versatile timer that uses the mains frequency as the clock signal, both 50Hz and 60Hz are supported.  It can time events ranging from 100ms to 99.9s with a resolution of 100ms, or up to 999s with a resolution […]

7400 competition entry: Discrete logic preamp

Haley0918 entered his Discrete logic preamplifier into the Open 7400 Logic Competition. Through some experimentation he figured out that a XOR gate shows some analog properties. By modulating the input between 0.8v and 1.2v the output was swinging between 1v-4v, making the logic IC a preamplifier with a gain of 7.5. You can check out […]

7400 Competition deadline has passed

The Open 7400 Competition deadline (October 21, 6am GMT) has passed. Today we will dedicate the blog to the numerous last minute entries.  Normal posting will resume tomorrow. On behalf of the 7400 Competition sponsors, and the Dangerous Prototypes crew, we thank you for taking the time to enter the competition. Sponsors of the Open […]

7400 competition entry: Police lights and siren for a toy car

Nathan entered his Police lights and siren for toy car into the Open 7400 Logic Competition: A Little Tikes Patrol Police Car was retrofitted with a battery-powered emergency police lights and siren system as an entry to the Dangerous Prototypes Open 7400 Logic Competition. The circuit design focuses on simplicity and efficiency of part utilization […]

7400 competition entry: 7400 Logic E-reader

Snorre built a Logic E-reader for the Open 7400 Logic Competition. It is a e-reader build completely from logic chips and 2 eproms. The e-books are displayed on a old analog oscilloscope. The front page says EEPROM instead of EPROM. I don’t have access to a burner right now, so i can’t fix it (ironically, […]

7400 competition entry: Illogical Dickson Doubler

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 […]