Mains frequency is pretty stable and it is unlikely that you have to measure it but if you have an emergency generator you might find this circuit useful as it will give an indication whether the generator is running too fast or too slow. Actually you can use the mains frequency to calibrate it by adjusting the 25K multiturn trimmer until it reads 0. The odd looking components values are easily obtained using standard values: 3777 is 3900 in parallel with 120K?, 4020 is 3900 and 120 in series, 570nF is 470nF with 100nF in parallel and 400nF is 4 x 100nF capacitors in parallel. Components should be chosen for their stability and precision. 1% tolerance would be ideal but 5% is acceptable so long as you measure them with a good meter.
Click here to download the full size of the above Circuit.
Click here to download the full size of the above Image.
Capacitors should be properly rated for direct connection to the mains and resistors should have a low temperature coefficient as it will adversely affect the zero setting and change the filters response. The 100?F capacitor could be occasionally reverse biased with a voltage of 0.1-0.2 V. There is no problem for the capacitor which is generously rated. Operation is quite simple: connect it first to the mains, wait about 4-5 minutes until all resistors reach their working temperature, calibrate, and then connect to the generator. Variation in the mains voltage will not change the zero setting but will make the meter more or less sensitive: for example, a reading of 51 Hz will show as 51.1 with a 10% supply voltage increase. Full scale deflection is around +/- 2 Hz. If you wish to accommodate a wider range of +/- 3.5 Hz, typical for a petrol driven generator, you have to change the 2.2K? resistor to 12K?.
WARNING! This circuit is directly connected to the mains and should be assembled in a box which will avoid access to any of its part and care must be exercised when calibrating the unit. If you live in the States or you have a 110 VAC, 60 Hz mains, you may try the second circuit: the reported values are calculated values, I did not actually test the unit. The odd capacitors values are easily obtained with the combination of standard values: 0.94 is 2 x 0.47 in parallel, 1.056 is 1?F + 56nF in parallel and 1.1 is 1 +...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: