• ### Summary and maybe future work?

The portable generator was able to induce a sine wave on the secondary coil for frequency range of 55-194 kHz, which achieved the main goal of the project.

However, the circuit seem to get unstable due to kickback of the coils when Potentiometer2 (filter) became small, with voltage spikes as large as 21 V peak to peak! This would cause the circuit to ‘crash’ and need to be reset. Thus for safety reasons the ‘shaping’ potentiometer (filter) is hidden within the box, not for user control.

Future upgrades could increase the stability of the circuit with an op-amp buffer, or an added transistor to amplify the current to drive the coils. A second potentiometer can also be added to increase the range of lower frequencies of the oscillating circuit to achieve the conventional 60 Hz.

If possible, a step-up transformer to can also be added to raise the output to 120V or 240V, which will greatly expand the portable unit’s usability.

i think it'd also be interesting to figure out the output current, and maybe test it out on other small AC-needing devices (and watch them die hahahahah).

• ### Testing with a Stubborn Load (EM Coils)

The Make book suggested that for 555 oscillating circuits similar to this, the frequency can be calculated with

I attempted to achieve greater frequencies by reducing R1 and R2, but the high current caused the resistors and chip to be hot. The constant k depends on the other components in the circuit. If I define k = 1440 as given in the book’s example, my maximum frequency should be around 260 MHz. However, the measured range of oscillator was only 55-194 kHz. This big difference is probably due to the k value due to other component’s differences.

The variable RC filter was controlled by potentiometer2 (P2). The resistance on P2 was varied to suit the frequency and smooth out the square waves.

When the frequency is greatly varied, however, another capacitor will need to be used to filter out the ‘extra’ higher frequency waves. So that's a problem with varying frequencies hmmm.