Serial asynchronous receiver


This is an RS-232 compatible receiver, implemented by using 74xx circuits.
Operation: the start bit switches the SR latch (74HC00) on, and the counters (74HC393) start counting up. The shift register samples each bit (from the Start bit until the 7th bit) just in the middle. At the end of the 7th bit (actually at the beginning of the Stop bit), the data of the shift register is loaded into the output latch. The circuit is reset just in the middle of the stop bit, so a new Start bit can be detected immediately.


---+       +-------+-------+-------+-------+-------+-------+-------+-------+-------+---
   | Start |   0   |   1   |   2   |   3   |   4   |   5   |   6   |   7   |  Stop 
   +-------+-------+-------+-------+-------+-------+-------+-------+-------+






2 x 30W HiFi stereo amplifier


The power amplifier is mostly based on the Videoton EA6383, though it contains some improvements. The biggest difference in my design is the use of Sziklai-pair instead of Darlington in the output stages, mainly because of better thermal stability. Other improvements include emitter degeneration and current mirror in the long-tailed pair section.



Assembled and mounted in its metal enclosure:



The preamplifier is a regular 2-stage opamp design. The first stage does the real voltage amplification and the second stage is the active tone control circuit, utilizing a Baxandall tone stack. Here is a very good source of audio related topics.






RF sweep generator


This simple sweep generator circuit can be used to align AM and FM receivers. It provides 455 kHz and 10.7 MHz frequencies and sweep output. The LFO is a simple schmitt-trigger relaxation oscillator, the depth of the sweep signal can be adjusted by varying its slew rate.






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