This is a PCB for simple DDS generator, wich based on development the author under the nickname Integrator. The digital part is implemented on an Atmega8-16AU microcontroller operating at a frequency of 16MHz and a resistive R2R DAC. From the DAC output, the signal goes to the buffer amplifier. Then it passes through an active low-pass Butterworth filter of the 4th order. Switch SW1 allows you to turn off the filter and remove the signal directly from the output of the buffer amplifier.

Signal form:

• sine
• triangle
• sawtooh wave
• rsawtooh wave
• ECG
• noise
• squarewave
• high speed squarewave
• PWM (rectangle with adjustable duty cycle)
• pulse (special shaped pulses)
• TV signal (stripes)

Frequency:

• Sine, triangle, sawtooh, rsawtooh, ECG: 1Hz - 111.1KHz
• Squarewave: 1Hz - 500.0KHz
• Squarewave (high frequency): 1MHz, 2MHz, 4MHz, 8MHz

PWM:

• 1Hz-99KHz
• fill factor 1% - 99%
• possibility of external synchronization

Special shaped pulses:

• Tmin. = Trise + Ton + Tfall + Toff = 8us
• Tmax. = Trise + Ton + Tfall + Toff = 4000000us
• number of pulses 1 - 65535
• possibility of triggering by external impulse

Supply voltage 12V

Signal amplitude 0 - 5V

Offset -3 - +3V

DAC bit depth 8bit

Sampling rate 1.78MHz

To reset the settings in the turned off generator, the encoder button is clamped, then power is supplied and without releasing the button, wait 5 seconds. After that, the settings in the EEPROM are overwritten to the default.

PCB was designed for the available me WH1602A-TML-CT# Winstar display. If other 1602 displays are used, the connector PBS-16 does not need to be installed, display can be connected to PCB with wires.

A properly assembled generator does not need tuning. The only adjustment needed is to set the output offset voltage to 0V at the middle position of the knob "Shift". To do this, in the "Sine" mode, the regulator R15 "Level" is set to the left position, the regulator R26 "Shift" to the middle position and through trimmer resistor R27 set to 0V at the generator output.

It is desirable to use resistors for DAC with 1% accuracy. The resistor value is not critical, it is important that all DAC resistors are the same.

Project Links:

DDS Schematics

DDS BOM

DDS component placement

DDS firmware

Project forum (russian)