The versatile IC timer 555 has yet another application as an analog frequency meter. By making use of a 556 integrated circuit, which has two 555 timers in a single package, an over-range indicator can be economically added to the meter.
Circuit Description of Analogue Frequency Meter with Over-range Indicator
When this meter is switched to the 50Hz range, any input frequency from near DC to 50 Hz produces a correct panel meter reading, i.e. a frequency of 42 Hz produces a meter reading of 42 microamperes. However, the analog frequency meter reading is correct when the input frequency exceeds 50 Hz, and therefore an LED over-range indicator flashes. If the range switch is then moved to a setting higher than the frequency, the LED stops flashing and the analog frequency meter again indicates correctly. For example, a 300 Hz signal could be measured on the 500Hz range, where the meter, would show 30 microamperes.
Here the input signal in the analog frequency meter is a rectangular pulse train; the pulses are differentiated to produce the negative spikes that are needed to trigger the timer. For a sine wave or sawtooth input signal, a Schmitt trigger might be used to generate the negative impulses for the input signal in an analog frequency meter.
PARTS LIST OF ANALOGUE FREQUENCY METER
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Resistor (all ¼-watt, ± 5% Carbon) |
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R1, R4, R12 = 1 KΩ R2, R6, R11 = 10 KΩ R3 = 4.7 KΩ R5 = 1.5 KΩ R7 = 47 KΩ R8 = 180 KΩ R9, R14 = 1 MΩ R10 = 100 KΩ R13 = 220 Ω |
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Capacitors |
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C1 = 15 pF (ceramic capacitor) C2, C3, C5, C6 = 0.01 µF (ceramic capacitor) C4 = 10 µF (electrolytic capacitor) |
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Semiconductors |
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IC1 (A + B) = NE556 T1 = 2N2222 T2 = 2N2955 D1 = 1N4148 LED1 = RED LED (over range indicator) |
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Miscellaneous |
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SW1 = Rotary switch Meter = 50 µA Panel Meter |
cant you build the above circuit with ic 741 and ic 555 timer please
if any one has it email the circuit diagram
You can just remove IC1A from the circuit and use single NE555 instead of IC1B, no over-range indication in this case. Or you can use two NE555 instead of one NE556. Just read datasheets and you will understand what you want.
I want to make this device with single NE555 adding 500kHz range and with DVM or DAM as indicator.
Is there any alternative for T2 ?
I can’t find it in my region and its odd to use such “heavy” transistor in this “light” circuit.
is you found any alternative for T2………?