The relative motion between a satellite and an observer causes a frequency shift known as the Doppler effect. Doppler is well-understood and can be corrected automatically by satellite tracking software...

This simple circuit will energize and de-energize a relay at the push of a button. Any type of momentary action push-to-make switch can be used. Pushing the button once - will energize the relay. And pushing it a second time - will de-energize the relay..

This circuit will give you a good, Accurate Watt Meter that can measure various power levels. In the Origional Article the Shunt was a .001 Ohm Copper Shunt giving a 1000 Watt Scale. However, because Most Circuit Breakers in homes are 15 Amps, I made my unit to have a range of Zero to 1500 Watts...

Static charge-electricity detector

The detector will sense static charges and free ions in the air. It can be used to indicate the presence of ion emission, high voltage, static electricity, and electrostatic fields. The ground can be an earth ground or a touching metal by your hand. the meter is 100uA range. and R3 potentiometer is by controlling the sensitivity of the detector...

The author described assembling this circuit on a 1"*1" perf board, I actually laid out a small PC board with excellent results. In this era of surface mount components, I think a much smaller version can be laid out on a PC board, allowing this circuit to be put inside even the smallest radios, such as Walkmans. If I do such a board, I will put the PC board artwork here...

The circuit is easy to use. When you press "E" - current through D2 & R9 switches Q5 on - and the transistor energizes the relay. The 12-volt output moves from the "off" to the "set" terminal - and the green LED lights. At the same time - R10 takes over the job of supplying base current to Q5. This means that - when you release "E" - the relay will remain energized...

This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc. The circuit is designed to use an electronic Siren drawing 300 to 400mA. It`s not usually a good idea to use the bike`s own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the "Siren" output. This can then be used to sound the Horn, flash the lights etc...

Please operate caution when building this power supply. It is run on, I believe, 120v ac current (standard US wall outlet) - and under the right circumstances 120 ac can kill you. Use a plastic enclosure if possible to decrease chances of short-circuiting...

Car Alarm Arming Beep Canceller

It's a great convenience that most modern cars come with a built in alarm, however it is nothing but noise pollution that the horn sounds when the alarm is armed. Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm. This circuit serves to silence the arming beep yet maintain the alarm by introducing a small delay into the signal. It sits between the alarm and horn relay. The alarm must provide a constant horn signal for at least 3 seconds before the horn relay is activated. That way the quick "beep" will never activate the horn relay, while the constant alarm signal will. ..

antenna tuner for better DX

Almost any receiver covering 540 kHz to 1600 kHz is suitable for broadcast band DX`ing, and there are a lot of them. But the antenna is another matter. If you are new to the hobby, or if you have been having trouble DX`ing those really difficult stations, you may find the answer to your reception problems in a properly constructed long-wire antenna - and the "Pi-section Coupler"...

Lead-Acid Battery Charger

The circuit is actually a half-wave rectifier. It only charges the battery on every half cycle. The plug pack doesn't like this as it leaves residual flux in the core of the transformer and causes it to overheat. But that's the only drawback with the circuit. The SCR turns on during each half cycle and current flows into the battery. A voltage is developed across the two 1R8 resistors (in parallel) and this voltage is fed into the 47u electrolytic. It charges and turns on the BC547 transistor. The transistor robs the SCR of gate voltage and the SCR turns off. The energy in the 47u feeds into the transistor but after a short time it cannot keep the transistor turned on. ..

Intelligently modifying the motor-drive commands to a robot can give you control finesse during competitions. Moving a joystick hard right, for example, might have different effects, depending on the robot`s speed and direction. Software running on an inexpensive microcontroller (in this case, an NEC (www.nec.com) PD78F9814) manages this control by calculating separate drive and adjust vectors and then combining the vectors and calculating the appropriate power ratio for two tread motors (Figure 1). This demonstration system uses a simple treaded toy vehicle to show how the ratio-drive concept works and requires no sensors in the vehicle...

As shown in the schematic diagram here, the astable multivibrator simply extends the modification that converted the bistable multivibrator to a monostable version of the circuit. Now, both transistors are coupled to each other through capacitors. Whichever transistor is off at any moment cannot remain off indefinitely; its base will become forward biased as that capacitor charges towards +5 volts. Once that happens, that transistor will turn on, thereby turning the other one off...

Figure 1 shows complete hardware schematic of the Night Light Saver V6.0. The AC line was protected F1, a 1A fuse. Any short circuit caused by saver`s components will blow the fuse. R1 and C1 limit current to the +5V zener diode, D3. R2 discharges capacitor C1 when power terminal of the circuit was opened. The super capacitor C2,+5V 0.01F filters DC supply. D4 acts as unidirectional switch for current supplied to MCU...

This is not a "do everything" mixer but it is ideal for what I need it for and it handles a line input just fine. I made it so all the jacks are in the front for easy access like a patch bay. The components I used were from things I just had at hand. For example the 10K pots are linear pots but I would of preferred to use log pots if I had them. I`m sure that the design could be a little different but I just kind of stumbled through it from scratch and it works really good. With the volume controls on full the output is about 3-6 db louder then the input which gives a little leeway for whatever the need...