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This add-on board is designed to provide a pair of balanced audio outputs for the High-Quality Stereo DAC (Digital to Analog Converter). Two 3-pin male XLR connectors are used for the new outputs and they can either replace or augment the existing unbalanced outputs without affecting their performance. Balanced audio is used in recording studios and on stage because of its improved noise immunity. Picture of the project:      This is due to the fact that the signal is sent differentially (ie, as two signals 180° out of phase) and then converted to a single-ended voltage signal at the far end. If any noise is picked up in the cable, it affects the two out-of-phase signals equally so that when the signals are subsequently subtracted, most of the noise is eliminated. Parts layout: In addition, the DAC’s performance at the balanced outputs generally exceeds that of the unbalanced outputs, although only by a small margin. The signal-to-noise ratio, frequency response and chann...

This little circuit indicates the basic integrity of a printed board, detecting 0V, positive supply voltage from less than 3V to 30V and floating parts. If the probe is floating, as it would be in a broken track, then both LEDs barely light up, since there is no current to drive the transistors, but if the probe touches 0V or a positive voltage one or other lights. A digital signal should light them in proportion to the mark-space ratio whereas the output of a circuit oscillating at a frequency rate below about 20Hz will cause the LEDs to flicker alternatively. The LEDs will illuminate always at a constant intensity, no matter the voltage supply used, because they are fed by a very simple FET constant-current generator (Q1). Circuit diagram: Circuit Board Checker Circuit Diagram   Parts: R1 = 22K R2 = 22K D1 = Red LED D2 = Green LED Q1 = BF245 Q2 = BC547 Q3 = BC557 Notes: The Black clip must be connected to the negative ground of the board under test. The Red clip should be connect...

Maybe we are more familiar with the term Minimum System AT89C2051 circuit, but this time I present a circuit which is not only a series of Minimum System AT89C2051 but more than that. The circuit is more deserves to be called Evaluation Board AT89C2051 and AT89C4051. Some of the advantages of circuit Minimum System AT89C2051 / AT89C2051 and AT89C4051 Evaluation Board which I was present this time, hardware-hardware support below: RS-232 interface, DB-9 Header for LCD display I2C, PCF8574 I / O extender AT24C04, I2C EEPROM