When I was first learning electrical engineering one of the terms I struggled with was negative voltage. How could a voltage be negative? There was ground and there was + voltage. To me, voltage was always a higher potential than zero.
I understand this is something most people don’t wake up in the morning and wonder about. Yet, it’s probably worth a short story.
My first encounter with this mysterious property of electricity came from working on audio synthesizers. In the early 70s I was intent on building musical synthesizers. I hadn’t yet moved to audio. One of the key components in a synthesizer is called the Voltage Controlled Oscillator (VCO). An oscillator is the sound source of musical notes in a synth. It generates the tones we hear when a keyboard note is pressed. In synths of old, differing voltages were used to set the frequency of the oscillator (hence the term VCO). Higher control voltages produced higher audio frequencies.
VCOs are not nuthin’ to design, so I searched for an integrated circuit instead. In those early years, there wasn’t much to find other than the Intersil 8038. This ancient IC did everything I needed. It took weeks to get a block of ICs mailed to me but finally, they came. I soldered up the chip according to the schematic and applied voltage. Nothing worked. In fact, the chip got hot and died. On the datasheet had been a reference for the control pin that required negative voltage. Having never heard of negative voltage, I figured it must have been a mistake and applied positive voltage instead.
Electrical engineering is quite unforgiving of wrong moves.
I had to crack open the books to learn what it all meant. Eventually, the IC became the basis of my musical synthesizer, but it forced me to learn about the idea of negative volts.
Here’s a simple way to think about negative voltage. If we take a battery and attach its + terminal to a loudspeaker’s red binding post, and its – terminal to the loudspeaker’s black binding post, we will cause the woofer to jump forward, towards the listener. That’s positive voltage. If we flip the battery around so the + terminal goes to the black binding post on the speaker, the opposite will happen. The woofer will move away from the listener. That’s applying a negative voltage.
If you’ve made it this far in the story you’ll have figured out it’s all relative.