Mark Neil - Microprocessor Course 1 Digital to Analog Converters

Example Product: Signal Generator Mark Neil - Microprocessor Course 2 A Signal Generator should be programmable. A user can use the the LCD display and the keyboard to change the:  Frequency scale  Amplitude scale  Offset on/off etc.  Waveform shape (Square, Sinusoidal, Triangle..) Analog control given by potentiometer Analog signal output by using a Digital to Analog Converter (DAC)

Digital to Analog Conversion Digital data representing an analog signal (for instance an MP3 file) sampled at a (usually) fixed time interval is fed to a Digital to Analog Converter The output is an analog waveform which is an approximation to the original analog signal Input Digital Data Digital to Analog Conversion (DAC) Output “Sampled” Analog Waveform 3 Mark Neil - Microprocessor Course

The 741 Op.Amp Mark Neil - Microprocessor Course 4 Summing Amplifier V out = - (V1+V2+V3)

The 741 Op.Amp Mark Neil - Microprocessor Course 5 R-2R Network to convert digital to analog

Operation II The basic operational idea of the DAC we will be using is simply to have a series of switches which control a resistor network Depending on which bits are set, the output voltage changes 6 Mark Neil - Microprocessor Course

The TLC7524 DAC For your analog signal generator you will be using an 8-bit DAC to convert an 8-bit data stream, from the ATmega128 ports, to analog signals of given frequency, amplitude and offset 7 Mark Neil - Microprocessor Course

Write Cycles of the TLC7524 The DAC has internal registers to store the input Data (1 Byte) and signals which control the write operation (CS*, WR*): 8 Mark Neil - Microprocessor Course

DAC Operation The output signal will need to be fed into an external op-amp Data should be put on the data bus using one of the ATMEL PORTs CS* can be held low 9 Mark Neil - Microprocessor Course

Schematic You can write numbers to the DAC in a similar way as with the 3-byte memory module using the ATmega128 Ports 10 Mark Neil - Microprocessor Course CS* : keep it enabled

Task Plan Mark Neil - Microprocessor Course 11 Design and construct a Signal Generator: The signals should be produced using a DAC and an Operational Amplifier driven by one of the ATmega128 ports. Verify operation by copying the input voltage read from the potentiometer to the DAC output