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MIDI Drum Machine
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Power Supply Schematic

Note: the new board will use only a single 5 volt supply, from the more readily available 7805 regulator in the common TO-220 package, and it won't need the powerfail warning signal and battery backup, since configuration will be stored in a small EEPROM chip.

Power Supply Schematic:

schematic diagram

This funny power supply creates 5 volts for the CPU and digital logic and +/- 5.7 volts for the Analog input circuitry. It also provides a signal that indicates when the power has failed, so that the 8051 can enter its power-down mode and protect the user's configuration is the 8051's internal SRAM.

Several component values are unmarked. The capacitor after the bridge rectifier should be a large value, such as 1000 µF (larger values are ok or multiple smaller capacitors may be connected in parallel). It should be rated for at least 25 volts. The small capacitor attached to pin 2 of the comparator should be 0.1 µF. The comparator is a LM311. The eight diodes are general purpose rectifiers, so 1N4007 or similar diodes may be used. The zener diode is 5.6 volts. The 7905 voltage regulator must be attached to a heatsink.

or skip to the firmware.


The MIDI Drum Machine, Paul Stoffregen and Rod Seely.
Designed and constructed Fall, 1991. Project status: Complete.
http://www.pjrc.com/tech/midi-drums/sch-pwr.html
Last updated: February 24, 2005
-- These drum-machine web pages are still under construction --
Questions, Comments?? <paul@pjrc.com>