The amount of light (e.g., controlled by the shadow of your hand) falling on the light-dependent resistor (LDR) in this project will determine the tone produced by the circuit. Extending your hand and keeping it over the LDR, you can control the tone produced by this circuit by letting more or less light fall on it. This is one of the applications for using this circuit as a feedback device.
Kirlian photography or bio electrography is the name of the process involving the registration and observation of star-like patterns produced by high-voltage electrical discharge in living beings and objects. The patterns are associated with the "aura" of living beings.
This is the most powerful generator of the three circuits described in this book. Voltages to 40,000 V, and even higher, can be produced and applied to the electrodes described in the previous projects. You may need to use thicker glass or plastic pieces to avoid being shocked by the higher voltages produced by this circuit. Although this is a high-power circuit, the current is very low, which reduces the danger of mortal shocks if any part of the circuit is touched. Of course, extreme care must be taken when working with high-voltage circuits, as there is al-ways a risk of shock.
The first circuit of the series is very simple (See note below) and can be built from a few cheap, easy-to-find parts. This simple temperature change monitor can detect variations of temperature in any small part of your body (your fingers, for instance) or other objects, allowing you to use this information to control some physiological function or simply monitor temperature changes in experiments. The circuit is powered from two AA cells, and the current drain is very low, providing battery life of several weeks.
Watching the movement of a needle to control physiological functions is one form of visual feedback, as shown. In this project, we provide an auditory project wherein information about temperature changes in our body is provided by alterations in an audio tone.
This circuit generates a number between 0 and 15 in a binary form. The numbers will appear with values between 0000 and 1111, given by the combination of four LEDs according to the table below.