Raspberry-Pi Based WAVEFORM GENERATOR

A waveform generator is a commonly used test and measurement instrument in electronics laboratories.

- PRASANNA WAICHAL, ARPITA WAICHAL, NIKITA THORAT, PRAGATI TODKAR

Waveforms of different functions, frequencies, and amplitude levels are often required to test the functionality of electronic circuits. Although the circuit presented is not a complete substitute for a laboratory-grade signal generator, it serves as a waveform/signal generator with widely used standard waveforms, such as sinusoidal, square, triangular, and linear forward and reverse ramps under software control.

Moreover, since it is completely software-driven, it provides the added advantage of an ‘arbitrary waveform generator’ allowing users to design and generate custom signal waveforms with adjustable rates (frequencies) or wave shapes. The device uses the popular Raspberry Pi SBC as the main host controller, along with a few easily available, low-cost components that both hobbyists and professionals can assemble quickly. The software is written in Python for the Raspberry Pi. Fig. 1 shows the block diagram of the Raspberry Pi-based waveform generator. The components needed for this device are listed in Table 1.

Circuit and working

Fig. 2 illustrates the circuit diagram of this waveform generator. It is built around a Raspberry Pi, an 8-bit serial shift IC (74HC595), and a few other components.

The working of the circuit is straightforward. As shown in Fig. 2, the core of this waveform generator is the voltage-output R-2R DAC, comprising resistors R2 to R17. This 8-bit DAC accepts digital input and converts it directly into a voltage output. Unlike a currentoutput DAC, there is no need for an external voltage-to-current circuit using an op-amp. Thus, this is a very compact circuit that requires no additional power. Further details about the working and operation of this R-2R DAC can be found in the October 2000 issue of EFY, in the article ‘R-2R DAC Based Waveform Generator Using PIC16C84 Microcontroller’. The output of this DAC is available at connector J1, which is labelled ‘DAC Output’.