Measuring the Flashing Time Interval of LED Lights in Toys

Abstract

Abstract:We have developed two methods to measure the light flashing time interval in toys. One method uses high speed video recording and a synchronous counter. The method starts by taking a short video clip of the flashing Light Emitting Diodes (LEDs) under test, together with the reading of an in-house designed synchronous counter which is phase locked to a cesium frequency standard. The flashing time interval is obtained by viewing the recorded video to search frame-by-frame for the time interval between two successive LED state changes. This method has a measurement uncertainty (k = 2) of less than 2 ms. The second method is a direct measurement with a time interval counter. A circuit with a photo-transistor converts the light signal to an electrical signal. A variable resistor is connected in series with the photo-transistor to tune the detection sensitivity such that it can work well in low illuminance conditions. The output signal is then amplified and fed to a time interval counter that is phase ...