- Yamada's SAR ADC project on Hackaday (brought to my attention by G. Davidge) required the use of negative voltage (+/- 9V, in particular)
- Op Amps typically require this so an investigation was undertaken to develop a straightforward way to achieve this using components ACES have ready access to in the DES.
What Was Known
- Batteries in series can be used to increase voltage but, as the graphic to the right suggests, tying the negative terminal of the first to the positive terminal of the second creates a common reference voltage for the remaining terminals (one a positive potential difference and the other a negative PD)
- We're not a big fan of batteries in the DES for a number of reasons so a breadboard solution using 9V AC/DC wall adapters was constructed.
- A review of YouTube possibilities yielded this useful video introducing the Wien-Bridge Oscillator that uses an LM741 Op Amp to generate a sinusoidal wave form. Thos is another asset ACES engineers could exploit to advantage.
- The breadboard prototype above was put to the scope for confirmation. The result appears below.
- In designing V1 of the +/-9V PCB it was decided to add both a 5V reference and Wien-Bridge Oscillator onto the standalone PCB.
- A photo of the soldered V1 appears below right. A ganged pot was a device I had never used before and found interesting.
- After testing V1 appears to deliver the voltage reference results expected.
- Running the sine wave signal through the scope yielded a result below. With horizontal divisions at 100 μS the frequency appears to yield 1370 Hz which might be audible if I ever get around to adding a speaker to the signal.
C. D'Arcy, 2023.