Showing posts with label channel. Show all posts
Showing posts with label channel. Show all posts
Wednesday, July 10, 2013
Simple 8 Channel DTMF Link Encoder
Generated millions of times every day by our telephone keypads, the eight DTMF frequencies were chosen so that the harmonics and intermodulation do not generate significant in-band signal levels. The signal is encoded as a pair of sine waves, ensuring that no frequency is a multiple of the other and the sum and difference between two frequencies does not match any single tone and that’s why DTMF sounds so ugly!T he DTMF encoder circuit show n here is based on the HT9200B tone generator device produced by Holtek and distributed by Futurlec among others. The encoder is complemented by a decoder elsew her e in this publication.
8-Channel DTMF Link: Encoder Schematic
The HT2900B is supplied as a nice old fashioned 14-pin device. It can be instructed by a microcontroller to generate 16 dual tones and (in serial mode only) 8 single tones from the DTMF pin output . It s 8 - pin ‘ younger brother’ the HT9200A provides a serial mode only whereas the HT9200B contains a select-able serial/parallel mode interface for various applications such as security systems, home automation, remote control through telephone lines, communication systems, etc.
A 74HC148 8-to-3 priority encoder is used to convert the ‘keypad’ information from S1–S8 into 3-bit tone selection words the HT9200B wants to see at its input. The ninth switch, S9, is connected to input D3 on the encoder chip. Pressing one of the switches S1–S8 generates a complementary 3-bit binary word at outputs A0, A1, A2 of IC1. IC2 then generates the dual tones accordingly to these binary codes.
Pressing S1–S8 generates the dual tones for DTMF digits C, B, A, #, *, 0, 9 and 8. By pressing and holding down S9 the DTMF digits 7, 6, 5, 4, 3, 2, 1 and D are generated.
To generate the eight single frequencies accurately a 3.58 MHz crystal quartz is connected to pin 2 and 3 of IC2. Pin 13 of the HT9200B supplies a DTMF signal of about 150 mV at a 5 KO load.
Pull-up resistor array R2 may be omitted if you substitute the 74HC148 with a 74LS148. R1 must be present in that case, otherwise it can be omitted.
The circuit consumes about 2 mA from a regulated 5 V supply. It should be easy to build on a small piece of prototyping board. link
Monday, April 1, 2013
Simple 3 Channel Audio Splitter
Simple circuitry, Passive high-quality amplification and distribution
This circuit is suitable to amplify and distribute the audio signals. The input audio signal is applied to the J1 and after passing through the P1, It is buffered and amplified by the IC1 prepared to redistribute. It has 3 outputs to drive 3 audio lines with 300 ohms impedance.
J1 = RCA Socket (See Notes)
P1 = 100K-Potentiometre
R* = 10K-100K
R1 = 560K
R2 = 1K
R3 = 2.2K
R4 = 2.7K
R5 = 2.7K
R6 = 330R
R7 = 330R
R8 = 330R
C1 = 100uF-25V
C2 = 100uF-25V
C3 = 100uF-25V
D1 = BZX79C18
D2 = BZX79C18
Q1 = BC337
Q2 = BC327
IC1 = NE5532-34
Notes:
- J1 will be RCA Audio input female socket.
- R* is on your choice it can be choose between 10K to 100K resistor.
- Output capacitor’s value is between 100uf to 470uf and power handling is 25V to 50V.
- You can power up this circuit via +12V/-12V regulated supply but you have to remove following parts Q1-Q2-C2-C3-D1-D2.
- Maximum power ratings +35V/-35V
Source : www.ecircuitslab.com/2011/05/three-channel-audio-splitter.html
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