Embodiments include methods and apparatus for determining whether a neurological event has occurred in a subject. The reference circuit comprises a first P-channel field effect transistor and a first N-channel field effect transistor. A silicon source is disposed in fluid communication with the gas path and is configured to be delivered to the gas path to maintain, in gas flowing in the gas path over the coating, a silicon mass concentration in the range from about 1. The light-focusing unit is to be disposed between the light-emitting components and the test object, receives the light emitted by the light-emitting components, and focuses the light on the test region of the test object. In one example, flyback transformers supply charge to lower capacity battery cells to extend battery output.