Design and application of electronic drum circuit TH3670C

Abstract: HT3670C is a CMOS VLSI chip designed by HOLTEK for electronic drum response applications. This paper introduces its internal structure, characteristics, functions and typical applications, and describes in detail its rhythm table and drum key switch functions.

1 Overview

Electronic drum is a phonograph instrument, and its chip is not like general audio IC. Its design and production are difficult and demanding. HT3670C launched by HOLTEK is a high-quality CMOS VLSI designed for electronic drum audio applications.

The HT3670C has a wide range of 18 instruments and 36 rhythms, which can provide a special amount of sound softness. In addition, there is a volume key for easy beat adjustment. In addition to the replay and demo key functions, this high-quality CMOS VLSI can also adjust the external keypad and control the internal sound processing circuit. The HT3670 is embedded with a full-featured 8-bit microcontroller, which can provide control for variable and multi-functional sound output. Its sound output is provided by a 4-channel Electronic Tone Synthesizer (ETS) and a 2-channel sound processing circuit.

2 Internal structure and packaging

The internal circuit of HT3670C mainly includes microcontroller, control register, distributor, 4-channel electronic tone synthesizer, 2-channel sound generator, multiplier and digital-to-analog converter (DAC) audio output/processing (OIP) circuit, etc. Its structural block diagram is shown in Figure 1.

The HT3670 uses a 40-pin DIP package, and its pinout is shown in Figure 2. Table 1 gives a description of its pin functions.

Table 1 Pin and solder joint function description

Table 2 Percussion instruments

3 Features and functions

3.1 Main features

The main features of the HT3670C are as follows:

●Low operating voltage (VDD): 3.3V～5.2V;

●High system frequency (fosc): 3.58MHz;

●Use RC type oscillator;

●Low standby current (ISTB): 2μA (typical);

●Three-channel 8-bit D/A audio output;

●Embedded "Holtek" 8-bit microcontroller;

● Capable of processing four-channel melody and two-channel sound;

●Eight-level master volume control;

● Use power on/off indicator music score;

●The alarm sound will be automatically cut off after 2 minutes;

●With 36 rhythms and 18 percussion effects;

●Capable of driving two 7-segment LEDs;

●The beat is adjustable.

3.2 Functionality

Compared to many drum instruments, the HT3670C electronic drum sound CMOS VLSI has the best flexibility and practicality in generating drum sounds and rhythm sounds. Each of the 13 percussion pads provided by the HT3670C can be selected from 18 percussion instruments. Using 6 selection keys, 36 fill-in sound rhythms can be selected to provide additional backing sound circuits. The embedded 8-bit microcontroller can be used to perform multi-channel input key control and internal electronic tone synthesizer control. After receiving the required action from the key, the microcontroller will generate and send the correct control code to enable the electronic tone synthesizer to generate the required drum signal. The sound output appears on two melody outputs and one sound output, and all drives are realized using current-type D/A converters. The internal hardware circuit also provides drive for two 7-segment LEDs connected to an external sound amplifier.

Table 2 lists the HT3670C and 18 percussion instruments.

Table 3 lists the rhythms of the HT3670C. These rhythms can be selected using the 6 tone selection keys and displayed by the LEDs. The numbers in Table 3 are discontinuous. There are actually 36 rhythms available (not 55). Numbers 6 to 9, 26 to 29, 36 to 39 and 46 to 49 do not exist.

4 Typical Applications

Figures 3 and 4 are typical application circuits of the HT3670C. In the circuits shown in Figures 3 and 4, if OPT1 is connected to VDD, the power supply will be automatically cut off, and if OPT2 is connected to VSS, the automatic bass chord will be turned on. Melody channels 0 to 1 are output from AUO1, and channels 2 to 3 are output from AUO2. In Figure 4, the buffer 74HC244 (74HC4050 can also be used) is used to increase the display brightness of the 7-segment LED. In order to have a better understanding of the working principles of these two application circuits, Table 4 lists the functional description of the electronic drum key pad switch.