Page 95 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

5089 is shown in Fig. 5.19. If you use a standard 3 4 (telephone)
keypad, you will lose the four functional DTMF codes associated
with the missing keys, therefore reducing the maximum number
of usable channels to 12.
Figure 5.20 is an encoder test circuit that uses an eight-position
dip switch. The dip switch takes the place of the matrix keypad;
with it you can test the operation of this encoder circuit and the
receiver (decoder) circuit. Notice when you turn a switch on, you
are grounding the pin it is connected to. Pins R1 through R4 and C1
through C4 are active low. Dip switches 1 through 4 are connected
to pins R1 through R4, and dip switches 5 through 8 to pins C1
through C4.

74

5.19 Pin out of 5089 DTMF encoder IC

VDD
1
15 9
5
XTAL
4
7
3
8
6 5089 14
13
12
11
16 TONE
OUT
4.7K
XTAL = 3.57 MHz
5.20 Schematic of encoder circuit using eight-position dip switch
Team LRN
Chapter five