Counters

To measure a high-frequency signal using an 8-bit µC, the time period of the measured frequency must be relatively close to the internal clock of the µC. For example, if the internal clock period is 1 µsec, then the maximum frequency that you can measure is 1 MHz in most µC applications.

This simple counter is useful for frequency measurements of various wireless equipments, especially transmitters, receivers and signal generators in VHF/UHF band.

The High Speed Function Generator was published in the professional electronics section of the Aug 1996 issue of Electronics Australia, and has proven to be extremely popular. The kit is no longer available from any of the kit suppliers.

This little circuit will help you to scan the line of a 220V live wire in the wall. The FET gate is connected to a capacitive metal sensor (which is usually a simple metal plate). When you hold the sensor close to the wall, the LED will indicate the current flow around where it detects the wire. Works on 9VDC.

To generate high voltages with proper insulation between the "hot node" and the rest of the circuitry, a car ignition coil can function in place of a high-voltage transformer. These coils have voltage ratings of approximately 20 kV, so you can use them to produce voltages around this value. Because you know the turns ratio of the coil, you can make a stable high-voltage source using a well-controlled voltage at the primary side (Figure 1).

This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a car.

This circuit is intended to indicate the power output level of any audio amplifier. It is simple, portable, and displays three power levels that can be set to any desired value. For a standard HiFi stereo power amplifier like the 25W MosFet Audio Amplifier described in these pages, the power output values suggested are as follows:

Use this circuit to test if the light coming from your 40khz IR emitter is really emitting the right frequency. The schematic says to use a GP1U5X ir module, but probably any 40khz detector module will work.. I used a GP1U26X module.

The two timers determine the allowable accuracy for the timer IC under test. Potentiometers P1 and P2 permit ready adjustment for the desired range. With power applied, all timers switch to the high state and begin their cycles. The output of IC1 inhibits the flip-flop for the interval T1. At T2, the output of IC2 goes low and inhibits any signal from the timer under test. The period between T1 and T2 is the time alloted for IC3, the timer under test, to complete its cycle and produce a low output.

The two timers determine the allowable accuracy for the timer IC under test. Potentiometers P1 and P2 permit ready adjustment for the desired range. With power applied, all timers switch to the high state and begin their cycles. The output of IC1 inhibits the flip-flop for the interval T1. At T2, the output of IC2 goes low and inhibits any signal from the timer under test. The period between T1 and T2 is the time alloted for IC3, the timer under test, to complete its cycle and produce a low output.

The 555-tester above is basically a led flasher circuit but with the 555 removed. Imagen the output being a square-wave pulse with a high and low pulse, and is so indicated by the two leds, one 'Hi' and the other one 'Lo'. When you have a good 555 under test, the hi and lo leds are flashing steadily. If you have a defective 555 you may get both leds off, one or both on steady, or one or both on faintly.

The standard circuit will display directly in Hz (1MHz max), and there is a seperate on board divider that will allow you to display directly in KHz (approx 40MHz max). Becuase the display reads directly in Hz or KHz there is no need for decimal point switching and the associated complexity. There are no switches or controls, simply feed the signal into one of two inputs and you have a direct readout in Hz or KHz.

You may have experiment with the values of R3 and R4 to get an accurate reading from the meter. Every meter is different, so a little bit of playing with the resistor values is required.

The latest versions of European CE-Marking standards include magnetic-immunity requirements for residential, commercial, industrial and audio/visual electrical and electronic equipment. Your product must be immune to magnetic fields from transformers or other sources. These fields can produce character “jitter” on CRT displays, distortion in audio equipment, or false readings in equipment containing Hall-effect devices or other electromagnetic field sensors.

I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees. The circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A different circuit would be needed to count the number of bees only going out or only coming into the hive.

This circuit uses a simple 4060 IC oscillator/timer that is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state. The time can easily be set from seconds to hours.

The circuit in Figure 1 includes all the necessary components to build a simple, low-power frequency comparator. The circuit centers around the operation of IC1, which integrates an amplifier, a comparator, and a voltage reference. The circuit feeds a digital signal to a bandpass filter comprising R1 through R4, C1, C2, and IC1's internal op amp. D1 rectifies the op amp's output signal, and the output of D1 charges C4.

The original application for the circuit in Figure 1 was to check the number of revolutions of an engine with only one LED as an indicator. The measurement of the number of revolutions usually involves sensors with a frequency output proportional to the number of revolutions. The circuit compares the frequency output of such a sensor with a lower and upper limit and gives a visual result, using one LED. If the frequency is below the lower limit, the LED remains unlit.

Here is a simple technique for measuring frequencies over quite a wide frequency range and with acceptable accuracy limits using a PC. It follows the basic technique of measuring low frequencies, i.e. at low frequency, period is measured for a complete wave and frequency is calculated from the measured time-period.

Plumbing a laboratory with a standard frequency makes a lot of sense if the lab uses multiple frequency counters, spectrum analyzers, and other frequency-dependent test equipment. Rather than spending time keeping all of the instruments' oscillators in calibration or buying expensive, high-precision oscillators, you can use the circuit in Figure 1 to distribute a single calibrated frequency source to the external-reference input of each instrument.