Digital oscilloscope is number one toll that should be standing on workbench. Depending on level of engineering you are doing scopes can be different. If you deal with simple problems that do not involve high frequencies or complex monitoring, then simple PC based scope can be you best choice. If you buy one, you can get cheap. Another way is to build one. Tomeko has build pretty handy tool that may be interesting to many enthusiasts.
His scope functionality didn’t end up with scope only. He also made an arbitrary waveform generator that is capable to output your desired signal shape. The base microcontroller for this miniscope is STM32f303CBT6 which features 128kB Flash, 32kB ram. It has full speed USB interface which is used to connect to PC. 4 fast ADC and two DACs. ADCs samples signals with 8-bit resolution at 7.2MSPS speed. PC demonstration software allows to see signals on both channels. Few parameters can be changed like time base or trigger. If you need signal generator, you can start waveform generator window, where standard signals can be generated like square. With arbitrary feature you can simply draw signal shape and generate it periodically at desired frequency. There is support for JSON export and import. Scope hardware is build on home-brew PCB which seems to be rare these days.
Embedds highly recommends EasyEDA for circuit and PCB design