Square wave

This is a very simple 5 watt CW TX based upon a TTL logic chip. There is just one "tricky" component and this is Cx. This component should have an impedance of about 10 - 50 ohms at the frequency of interest. If you wish to reduce the transmitter power, increase the value of Cx. It is Cx which causes the square wave from the output transistor to approximate a sine waveform. The value of Cx is the price of simplicity in this TX.

Using this circuit you can convert the 12V dc in to the 220V Ac. In this circuit 4047 is use to generate the square wave of 50hz and amplify the current and then amplify the voltage by using the step transformer.

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. 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.

This is a good and fairly efficient flyback driver circuit. All parts can be obtained easily from Radio Shack, including the MOSFET. This circuit uses a 555 timer IC to pulse a 2N2222 with square wave at a frequency that is set by the capacitor and the potentiometers. The 2N2222 then drives the gate of the MOSFET and the MOSFET delivers the pulse to the ten turn winding on the flyback. If you build this circuit you will have to adjust the potentiometers until you get the longest arc possible. The circuit will run from +12VDC to +15VDC at about 3A.

Here is a very simple circuit that will provide high voltage (15-40kV) sparks using a common ignition coil. The input is 12VDC at around 5 to 6 amps. Mine produces sparks that are about 3/4" to 1" in length. A 2N3055 NPN power transistor is pulsed with a square wave signal that comes from the 555 timer IC. The frequency of the pulses depends on the resistors between pins 7 and 8 and between pins 7 and 6. The pulse is also dependent on the capacitor. You can experiment with these values.

This circuit provides up to 20V output from a regular 13.2V automotive battery, to enable constant current charging of nicad battery packs up to 15 cells at 1.2V (18V total). IC1 is a Linear, Audio Power Amp (10W) and was orginally designed for car radios by Toshiba. Several replacement types can be used, like the ECG1288, NTE1288 and other substitutes will work fine. In this circuit, with S1 set in the 'boost' position, IC1 is used to form a squarewave oscillator, and by coupling this square wave to the 13.2V battery supply via D1 and D2 to obtain over 20 vdc. If this is not needed, S1 is left open (normal).

Infrared remote controls are using a 32-56 kHz modulated square wave for communication. These circuits are used to transmit a 1-4 kHz digital signal (OOK modulation) through infra light (this is the maximum attainable speed, 1000-4000 bits per sec). The transmitter oscillator runs with adjustable frequency in the 32-56kHz range, and is being turned ON/OFF with the modulating signal, a TTL voltage on the MOD input. On the receiver side a photodiode takes up the signal.

The 74AC240 stepper driver works by alternately enabling each half of the buffer. Only one half can be enabled at a time. Let's assume that the top half of the driver is enabled. U1A & U1B along with R8, C1, and the input protection resistor R7 form a square wave oscillator. The outputs of U1A & U1B directly drive one coil of a bipolar stepper motor.

Taking advantage of some new voltage comparators, this circuit can produce a nice square wave signal while drawing only 1.6 microamps. With the inclusion of a diode, the circuit can also produce short pulses instead of a square wave signal.

If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency.

Yes you can turn flip/flop ICs into low current oscillators. This schematic shows you how.

This circuit uses a single CMOS inverter to form a series resonant LD oscillator. The values shown set the oscillation at about 125KHz buth other frequencies are possible by changing the main LC values.

I have used this parallel resonant LC oscillator circuit countless times. The oscillator frequency is determined by the inductor and capacitor values. I have shown an adjustable inductor to make it easy to set the frequency to a specific value. Once set the frequency is fairly stable over supply voltage variations and temperature changes. The values shown are for 125KHz but the frequency can range from tens of kilohertz to tens of megahertz. With a 74HCU04 type inverter, it will oscillate down to about 1.5 volts.

By changing the supply voltage fed to a classic 4584 Schmitt trigger type oscillator, the oscillator frequency can be changed over a range of 50:1. A 74HCU04 inverter is used at the output of the 4584 to maintain a constant TTL logic level signal.

This circuit is similar to CMOS INVERTERS FORM 125KHZ OSCILLATOR but adds more invertors in parallel to deliver more power. The values shown are for 125KHz.

This circuit is similar to CMOS INVERTER 125KHz LC OSCILLATOR but adds even more inverters in parallel to deliver yet more power. The values shown are for 125KHz

If truly low power oscillators interest you, this circuit draws a mere 2 microwatts (500nA) from a 6v battery. It uses a very inexpensive C-MOS IC to produce a frequency of 2Hz. However, by changing the component values you can push it to 300Hz.

This circuit works much like the classic 555 timer, but draws only about 1.5 microamps from a 3 volt battery. It is highly stable under varying temperature and supply voltages.

This classic circuit draws only 200 nanoamps from a 1.5v supply.

The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed. The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed. The method keeps the standby power consumption to a very low 1uA when used with a 3v supply.