Archive for April, 2008
Infrared headphones transmitter
The transmitter offers a optical link (infrared) for headphones. Three infrared leds (ir) are polirised by T1 current, P1 is used to adjust the current level . Current consumption of this headphones infrared transmitter is about 60mA at 9V. Maintain separated adapter ground and audio signal ground to prevent current reactions thru LED.
The optical link [...]
27MHz Fm Narrow Band transmitter
NBFM or Narrow Band Frequncy Modulation is used in this 27 MHz fm transmitter circuit schematic. This circuit is an application by Motorola MC2833 - VHF transmitter with FM modulation and narrow band in a single chip.
The output power is 10mW (+10 dBm) and the coverage is 10 - 20m.
P1 is used to adjust microphone [...]
Microphone amplifier with low noise
This low noise microphone amplifier is build with MAT02 produced by PMI. This mic amplifier is very performant and has a very low noise level. The amplification can be 20dB or 23.5dB (10x or 15x ) selected by S1.
The output impedance is 70 Ω at 23.5 dB gain and with R3 = 220KΩ the input [...]
