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MIDI Drum Machine Main Page Features Photos Schematic CPU Section Analog Input All Inputs Power Supply MIDI Port Front Panel Circuit Board Layout Firmware MIDI Protocol Details

Main Schematic, CPU Section

TODO: add some explaination about what these chips do, and hopefully that text will have links to the other schematics.

TODO: describe pinouts of the 23 conductor ribbon cable.

TODO: The EPROM is a 28C16 (27C16 will also work). The 27C64 is an error. The pin numbers shown should be correct for the 24 pin 28C16, not the 28 pin 27C64.

TODO: Does it really work with the simple R-C reset circuit. We had a lot of trobule with that, and went to a few different circuits. What was the reset circuit that finally ended up in the working unit.

TODO: The 82C55 chip select (pin 6) is actually connected to pin 10 on the 74HC138 chip, not pin 11 as shown. Need to fix the schematic image.

TODO: Create a page with a complete parts list

Other Schematics:

• Simplified Analog Input Schematic
• Complete Analog Input Schematic
• Power Supply Schematic
• MIDI Port Schematic
• Front Panel Schematic
• Wiring Schematic - not on-line yet

  Note: This schematic is where most of the changes are planned for a new board. The 82C55 and 7 segment decoders on the display board will be changed to a group of shift registers on the display board, so that the 82C55 and the large number of wires won't be needed. The ADC0804 will be replaced with a serial interface ADC chip, and the 8051 will be replaced with a 89C51, so that the 27C16, 74HC373 and 74HC138 won't be needed. The main idea is to greatly reduce the number of wires, so that people who attempt to build the design without a printed circuit board will have far fewer wires to interconnect, and most wiring errors will result in only a portion of the drum machine not working, instead of having the entire thing dead and no reasonable way to troubleshoot. The new board will also only require a single 5 volt supply and will use an inexpensive EEPROM chip instead of battery backup.

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