Simple Digital Theremin Circuit

Here’s a design circuit for theremin circuit uses digital component, so we can call it a digital Theremin. This circuit employs logic inverter 74C04 or CD4069 hex inverter and CD4046 phase-locked-loop (PLL) IC. The CD4069 logic inverter is operated as a fixed-frequency oscillator with frequency around 100kHz. The CD4046 is operated as a variable frequency oscillator which is adjustable around 100kHz. The exact center frequency of the on-chip oscillator is determined by R4, C2 and R3. This is the figure of the circuit;

The frequency of variable oscillator frequency circuit can be shifted several kilohertz by moving your hand approaching the antenna since the C2 and the antenna form an equivalent parallel capacitance. The frequency of the variable oscillator should be set to the same frequency of fixed oscillator when there is no hand or human body close to the antenna. This calibration is done by adjusting the zero control R4 pot with this simple rule: If both oscillators (the fixed and the variable) are set to the same frequency then the Theremin will produce no output (silent). This Theremin circuit will start producing audible tone if you move your hand approaching the antenna since it will shift the frequency of the variable oscillator. You can play this Theremin circuit by moving your right hand around the antenna and at the same time turning the volume knob R5 with your left hand. [Circuit diagram source: seekic.com]

Super Simple Inverter Circuit

This is a design circuit of a simple inverter that can be used to power fluorescent lamp and a small strobe. This circuit will produce over 400VDC from a 12 VDC, 2.5 A power supply or marine battery or an auto. This circuit is very simple because it does not require custom transformers or coils. Also all components are readily available. This is the figure of the circuit;

 

The output of this circuit depends on the input voltage. If we use the component values given, we will get offer 400 V from 12 V supply and charge a 200 uF capacitor to 300 V in under 5 seconds. We must use a good heat sink because Q1 does get quite hot. D1 is used to prevents significant reverse voltage on the B-E junction and provides a return path for the base drive. R2 is used to limits surge current through D2.

WARNING: Output is high voltage and dangerous even without large energy storage capacitor.  With one, it can be lethal.

Stabilized 3V Voltage Source/Reference

This LM10 circuit can be used as low voltage low current voltage source or reference. This circuit regulate the voltage from the power supply to give a very stable output. This is the figure of the simple circuit diagram;

The minimum voltage level for powering this circuit require only 0.2V above the output level, showing the low drop out (LDO) feature of this circuit. [Circuit diagram source: National Semiconductor Application Note]

Light Level Droplets Detector Circuit

Here’s a design circuit for Low-Light Level Drop Detector. This circuit utilize self-biasing configuration to detect small changes in light level. This circuit usually used in monitoring very low droplets rates. The collector of the transistor gives feedback that is used to stabilize the bias of the photo darlington. This is the figure of the circuit;

 

The effect on optical performance is reduced by a high base-source impedance that is produced by The 10-μF capacitor and 10-MΩ resistor. When there is a liquid drop is detected by the detector, the light that reach the chip is momentary decreased causing collector voltage to momentarily rise, then output signal is generated. Due to mechanical spacing system constraints and output power constraints on the LED, the initial light bias is small. A fraction of this  initial bias is the change in light level. This fraction is caused by stray light paths and drop translucence. When biased, the output signals level is still acceptable because the photodarlington  has high sensitivity. This compares with unacceptable bias point stability and signal levels when biased conventionally, like signal output across the collector bias resistor and base open. [Circuit diagram source: seekic.com]

Five Decade Dynamic Light Level Meter Circuit

Here’s design circuit for a Portable light-level meter circuit with five-decade dynamic range. This uses a single cell battery as the power supply. To calibrate this circuit, use an appropriate illumination, then adjust R2 so that the output equals the reference. This is the figure of the circuit;

To make this circuit give output meter follows standard light meter, adjust R2 and R6. Maybe there is an error at the scale extremes because the log slope is not temperature compensated. An infrared-stop filter is recommended for this circuit because silicon photo-diodes (D1) are sensitive to near-infrared light. This circuit will give a excellent results if an appropriate correction filter is applied and a blue-enhanced photodiode for D1 is used. [Circuit diagram source: National Semiconductor Application Note]

Burglar Alarm Works for Both N.O and N.C Contacts

Unlike other alarm circuit that provide normally-open only or normally-closed only configuration, this alarm circuit work for both configurations. The mechanism of this alarm circuit is very simple, that the output will be active (Q1 transistor will be conducting) if IC1 or IC2 “high”. This is the figure of the circuit;

If R2 is open, then IC1 output will be high since the non-inverting input voltage will be tied to V++. At this condition, IC2 will be low but it’s fine since the output of IC2 is connected through a diode to prevent ground short.  If R2 is shorted then the voltage at pin 3 IC2 will go higher than the voltage at pin 2, so the output of IC2 will be high. At this time the output of IC1 will be low, but again, a diode (D1) will prevent the output to get shorted.

12V to 120V Power Inverter Circuit

Ever needed a low power 120volt AC power source for your car, van or truck? Well this circuit should do the trick for you. It will supply 15 watts of AC power to a device. It should power lamps, shavers, small stereos and small appliances. If you draw to much power the circuit will shut down all by itself. This is the figure of the circuit;

The output of this circuit is a square wave so there may be some noticeable hum on audio units plugged into it. To reduce some of the hum increase the value of the output capacitor which is at .47uf now. That transistor in the circuit are high power PNP transistors. Radio Shack part number 276-2025 are good ones to use or TIP32. The transformer is a 24 volt 2 amp center tapped secondary Radio Shack part number 273-1512 or equivalent.