next up previous
Next: Source Code Up: DTMF Encoder(Generator) Previous: DTMF Encoder(Generator)

Hardware

The following is the connection of hardware:
system clock:
interal RC osc. 8MHz/1 = 8 MHz
(lfuse=0xe2)

My SC1602BS*B LCD :
HD44780 compatible

LCD-PIN	mega48(solderless board)
 2 VSS	 (GND)
 1 VDD	 (VTG)
 3 VO	GND(0v)~5v (Infact when V0 > 1.8v, nothing can be seen.)
 4 RS	PB0
 5 RW	PB6
 6 E	PB7
 7 B0	GND
 8 B1	GND
 9 B2	GND
10 B3	GND
11 B4	PC0
12 B5	PC1
13 B6	PC2
14 B7	PC3

4x4 Keypad:
column1 --> PD0
column2 --> PD1
column3 --> PD2
column4 --> PD3
row1 --> PD4
row2 --> PD5
row3 --> PD6
row4 --> PD7



DTMF output:

1) if connect like this:(NO RC lowpass filter)

(ATTENTION!
IF OC1A connect a speaker(without amplifier),
DTMF decoder cannot detect signal.)

PB1(OC1A)
|
|
v
DTMF DECODER
CIRCUIT
INPUT(LC7385)

the LC7385 seems decode well(without problem),
but the waveform  (by oszifox) is rect wave.

2) if connect like this:(with a RC lowpass filter)

(ATTENTION!
IF OC1A connect a speaker,
or a speaker connected through the RC fliter(the sound is very weak),
DTMF decoder cannot detect signal.)

PB1(OC1A)--->/\/\/\/\(R)----| |(C)--->GND
			|
			|
			|
			v
		   DTMF DECODER
		   CIRCUIT
		   INPUT(LC7385)
	
R= 1K ohm, 560 ohm or 470 ohm
C=100 nF (104)
will generate DTMF wave fine,
and can be decoded well by LC7385.

3) DON'T CONNECT like the following, just for test!
if connect like this:(without RC fliter but through a amplifier.)

this way can generate dtmf sounds (not strong, just can be heard) but
the dtmf decoder CAN NOT decode well, sometimes will fail to decode!!!

but the wave is rect.


                            SPEAKER+
                              |
                              |----------->DTMF DECODER
                             --            CIRCUIT
			     C=220uF       INPUT(LC7385)
                             --
			      |	     
                              |
		            /--/\/\/\/\(100)---VTG
PB1(OC1A)--->/\/\/\/\(1K)--|
			    \-->GND
			     


---
note:
RC lowpass calc:
F_cutoff=1/(2*pi*R*C)
---

Instead of schematics, source code also contains hardware informations and technical notes, please read it for details.



sun ge 2007-10-24