Abstract: An electronic circuit for generating a trapezoidal excitation waveform includes a controllable frequency source and a trapezoidal waveform generator. The controllable frequency source generates a source waveform that, upon energization thereof, has an initial frequency value, and decreases in frequency to a substantially constant frequency value a time period after energization. The trapezoidal waveform generator receives the source waveform and, in response, generates a trapezoidal waveform at least when the source waveform frequency attains the substantially constant frequency value.

Abstract: A window guard assembly having a first stationary frame rigidly attached to a window opening having a second frame hingedly attached thereto and sized to closely fit within the first frame. A grate is rigidly attached to the second frame. To prevent unauthorized entry, a channel attached to the second frame has a pair of locking bars slidably mounted in the channel and movable into engagement with apertures in both frames to lock the second frame in its closed position. A lever handle and extension arm are pivotally attached to the locking bars to cause movement between their locking and release positions.