This circuit is an universal frequency generator which you can use in numerous frequency and time period testing applications. It is primarily well suited for a gate pulse generator in frequency counters.
The circuit is capable of generating an entire range of reference frequencies such as 1 Hz, 5 Hz, 10 Hz, 50 Hz, 100 Hz, 500 Hz, 1 kHz, 5 kHz, 10 kHz, 50 kHz, 100 kHz, 500 kHz, 1 MHz
The center of the circuit design is a 1 MHz crystal oscillator configured using a couple of NAND gates.
A 3rd NAND gate acts like a buffer at the output of this oscillator output of this oscillator, dividing down by a number of 7490 decade counters.
These incorporate a divide-by-2 stage accompanied by a divide-by-5 stage, that suggests that along with dividing the reference frequency down to 1 Hz in decades, signals of 500 kHz and lower values up to 5 Hz are likewise obtainable.
All these signals are specifically useful where gate pulses for counting frequency become necessary. For instance, the 5 Hz output will give you positive pulses of 100 ms width, thus when the frequency of a 10 MHz signal is tested, a gate pulse of this length might allow through 11500,000 cycles of the signal to the counter, presenting a display of 10,00000.
Alternatively, for time calculations the 1 Hz to 1 MHz outputs tend to be more beneficial. As an example, while computing a single second interval, 1,000,000 cycles of the 1 MHz output could be measured, offering a display of 10001300.
PCB Design
The PCB design and structure is very stream-lined and effectively presented. The outputs are obtainable across the lower edge of the board layout diagram. There exists one extra NAND-gate in the bundle intended for the oscillator, which can be employed as the gate in frequency counter applications.
The wiring contacts to this are introduced at the top right corner of the board. The oscillator frequency could be tweaked to precisely 1 MHz through the trimmer capacitor.
The ideal way of accomplishing this is by using an oscilloscope to examine the 100 kHz output with the 200 kHz Droitwich reception, and applying Lissajous figure. The trimmer must, naturally, be fine-tuned until the Lissajous number stops rotating.
Crystal Controlled Time base Generator
This precision crystal controlled time base circuit is constructed utilizing common easily available CMOS ICs and a inexpensive crystal. This circuit provides the user the configurations for obtaining 50 Hz, 100 Hz or 200 Hz. The 50 Hz reference frequency can be normally applied as a time base for calibrating electronic clocks, frequency meters and many others. IC1 is made up of an oscillator and a 20 divider.
Assuming that the oscillator loop is accurately calibrated through C2, the output at pin 3 (Q14) will generate a 200 Hz square wave. By using the two flip-flops from IC2 rge resulting square wave voltage is subsequently divided by 2 and after that by 4 contributing to a couple of additional outputs of 100 Hz and 50 Hz.
How to Calibrate
The 50 Hz being generated from pin 1. Hobbyists possessing a frequency meter can easily calibrate this crystal controlled time base generator circuit by merely hooking up the meter to pin 7 of IC1 (Q4) and fine-tuning C2 until a display of 204.800 Hz is seen on the meter.
As a topic of curiosity, any user not having a frequency meter probably should not lose heart, because adjusting the trimmer C2 to around at the center point, might be just enough to get adequate precision for the majority of applications.
The 100 Hz output is advantageous for the designing of digital counters.For this particular application we recommend that a 1 : 10 divider IC (like the IC 4518) is attached to the 100 Hz output pin. The power supply specifications are: between 5 .. . 15 V and 0.5… 2.5 mA.
