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68HC11 Based Function Generator
by Michael Ellis

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This site contains complete schematics and code for a 68HC11 based frequency counter, square wave synthesizer, sine wave synthesizer, programmable filter, capacitance and inductance meter, with a digitalker speech synthesizer output. Project specifications are given below.

External Picture
Expanded Block Diagram
Keypad Configuration
Operating Instructions
Circuit Board Descriptions
SPI Example Program


Digitalker List (Prebyte 00)
Digitalker List (Prebyte 01)
Program Flowchart
Memory Map
Measuring Capacitance
Measuring Inductance
The Function Generator Code

Frequency Counter 1 Hz to 9.999MHz, 1M ohm input impedance, 0.25 v rms to 50 v rms input
Square Wave Synthesizer 1Hz to 1 MHz, 3 digit PLL accuracy, 5 volts, or 12 volts digital output
Speech Synthesizer The 68HC11 uses a speech synthesizer chip (instead of a display) for verbal output
Sine Wave Generator 1Hz to 100 KHz, 0.02% distortion, 10, 1, or 0.1 volts peak-to-peak output with 3 digit PLL accuracy
EEPROM Programmer Changes to the 68HC11 EEPROM can be programmed directly from the keypad on this instrument without a terminal or computer. Minor software patches can therefore be done directly from the keypad.
Programmable Filter The 68HC11 controls an analog state variable active filter that can be set for lowpass, bandpass, or highpass (2-pole) function with the cutoff frequency controlled by the 68HC11 from 1 Hz to 100 KHz. Shifts in the analog components due to temperature are automatically compensated for by the 68HC11.
Capacitance Testor The 68HC11 controls circuitry that will measure capacitance from 1 pf to 0.1 uf with 1 pf resolution.
Inductance Testor The 68HC11 controls circuitry that will measure inductance from 1 microhenry to 0.1 Henries with 1 microhenry accuracy.
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