# Tag Archives: Frequency

### Electricity Frequency Meter

This project is about an accurate mains frequency meter that has a bar-graph displaying the relative deviation from nominal frequency. It can work with 50Hz and 60Hz systems.

An article by Dieter Laues in the February 2012 issue of Elektor inspired me to get my soldering iron out. The article described how by measuring the frequency of the mains electricity supply in any socket, the relative load across the entire electricity network could be determined

### Battery Powered Frequency Meter (0 to 20kHz)

The circuit is a simple digital frequency meter that is made of a frequency-to-voltage converter and an analog-to-digital display converter that can be operatedfrom a single 9-volt battery. The TC7126 ADC generates the voltage required by the TC9400 FVC with internal regulators. The TC7126 is designed to directly drive a 3-1/2 digit, non-multiplexed LCD display so no digital conversion is required.

The input circuit is made up of a current limiting resistor (33kΩ), a DC blocking capacitor (0.01µF), a clamping diode (1N914), and a biasing resistor (1MΩ). The diode acts as a soft clamp to prevent negative going transitions from latching the comparator input and the 33kΩ resistor limits the current during the positive transitions. The gain (VOUT vs. FREQIN) of the TC9400 is determined by the charge-balance capacitor and the integrator feedback resistor (620kΩ) that has been selected for an output of approximately +2V (referenced to ANALOG COMMON) with frequency input of 20kHz. The bias resistor (12kΩ) determined the input threshold of the comparator and has been selected for an input sensitivity range of 250mV to 10V peak-to-peak of a sine or square wave on the input of the FVC.

The TC7126 will have a maximum positive input of about 2V since the input is referenced to ANALOG COMMON that is only 3V below V+. The internal voltage swing of the integrator does not have the same limitation because a positive input results in a negative swing of the integration. A fully charged battery will give a range of about 6V. The integration components (1MΩ and 0.047µF) at pins VBUFF and VIN are selected, in conjunction with the oscillator frequency to have an integrator ramp amplitude of about –3V with a 2V input from the TC9400. The oscillator is set up to run at 48kHz (150kΩ and 50pF) for maximum rejection of stray power-line pickup. This will result in the TC7126 running at three conversions per second.

Battery Powered Frequency Meter (0 to 20kHz) – [Link]

### 100MHZ Frequency Counter with PIC16F628A

This project shows how to build a very simple yet very useful tool that every DIY enthusiast should have in his lab: a 100MHz+ frequency counter.

The schematic is fairly simple and straightforward and uses a PIC16F628A microcontroller for measuring frequency and a high speed comparator for signal amplification and conditioning.

The microcontroller uses its internal 4MHz oscillator for the CPU clock. Timer1 uses an external crystal resonator (watch crystal) with 32768Hz frequency for setting the 1 second time base.

Timer0 is used to count the input signal at pin RA4.

100MHZ Frequency Counter with PIC16F628A – [Link]

### Ovenized crystal oscillator frequency stability

E. Schrama @ ejo60.wordpress.com uses an Arduino and a DCF77 time signal receiver to test the stability of an ovenized crystal oscillator running at 1 MHz.

In this experiment I will use an Arduino and a DCF77 time signal radio receiver to measure the stability of an ovenized crystal oscillator running at 1 MHz. It demonstrates that 50ppb (or 50 milliHerz) can be achieved on the short term, whereby an aging effect of 0.1 ppb per day is demonstrated with a 18 month long dataset. The output of the 1MHz oscillator is fed into a 248 counter and six 74HC165 parallel in, serial out (piso) conversion ICs that are controlled by an ATMEGA 2560, the circuit is described here. With this setup running at 1 MHz you get a rollover every 10 years, the resolution is 1 microsecond. In principle you could do this also with an Arduino but I decided for this set-up since I already had most of the components left over from an earlier experiment.

Ovenized crystal oscillator frequency stability – [Link]

### Frequency counter using arduino

by praveen @ circuitstoday.com:

Many guys here were asking for a frequency counter and at last I got enough time to make one. This frequency counter using arduino is based on the UNO version and can count up to 40KHz. A 16×2 LCD display is used for displaying the frequency count. The circuit has minimum external components and directly counts the frequency. Any way the amplitude of the input frequency must not be greater than 5V. If you want to measure signals over than 5V, additional limiting circuits have to be added and i will show it some other time. Now just do it with 5V signals.

Frequency counter using arduino – [Link]

### Frequency and Phase Locked Loops (PLL)

by JIHAI ZHANG @ edn.com:

The purpose of a PLL is to generate a frequency and phase-locked output oscillation signal.

To achieve this goal, prior art essentially functioned by frequently changing the PLL output frequency according to the phase error (i.e. the faster/slower phase relationship) to generate a momentary, but not static, frequency and phase locked output oscillation signal. This frequent back-and-forth change in VCO frequency creates significant Jitter and a longer settling time because when phase is correct (locked), frequency is likely wrong (unlocked), or when frequency is correct (locked), phase is likely wrong (unlocked).

Frequency and Phase Locked Loops (PLL) – [Link]

### Low-Frequency Converter

Among the signals below 550 kHz are maritime mobile, distress, radio beacons, aircraft weather, European Longwave-AM broadcast, and point-to-point communications. The low-frequency converter converts the 10 to 500 kHz LW range to a 1010 to 1550 kHz MW range, by adding 1000 kHz to all received signals. Radio calibration is unnecessary because signals are received at the AM-radio’s dial setting, plus 1 MHz; a 100-kHz signal is received at 1100 kHz, a 335-kHz signal at 1335 kHz, etc. The low-frequency signals are fed to U1, a doubly-balanced mixer.

Transistors Q2 and associated circuitry form a Hartley 1000-kHz local oscillator, which is coupled from Q2’s drain, through C8, to U1 pin 8. Signals in the 10 – 550 kHz range are converted to 1010 – 1550 kHz. The mixer heterodynes the incoming low-frequency signal and local-oscillator signal. Transistor Q3 reduces U1’s high-output impedance to about 100 Ω to match most receiver inputs. Capacitor C15 couples the 1010 – 1550 kHz frequencies from Q3’s emitter to output jack J3, while blocking any dc bias.

Inductor L6 couples the dc voltage that’s carried in the rf signal cable from the receiver/dc adaptor. The dc voltage and rf signals don’t interfere with one another; that saves running a separate power-supply wire, which simplifies installation at a remote location. Capacitors C14 and C13 provide dc supply filtering.

### Freq Show: Raspberry Pi RTL-SDR Scanner

Freq Show: Raspberry Pi RTL-SDR Scanner is a new guide in the adafruit learning system:

Have you ever wondered what’s in the radio waves zipping invisibly around you every day? Software-defined radio (SDR) is a great tool to explore radio signals using a computer and inexpensive radio tuner. With SDR you can examime many radio signals such as FM radio,television, emergency & weather radio, citizen band (CB), and much more.

Although dedicated SDR hardware like the HackRF allow you to tune an immense range of the radio spectrum, you can easily get started with SDR using a Raspberry Pi and inexpensive RTL-SDR tuner. Inspired by the HackRF PortaPack, this project will show you how to build a small portable SDR scanner using a Raspberry Pi, PiTFT, and RTL-SDR radio dongle. With the Raspberry Pi Freq Show RTL-SDR scanner you can visualize the invisible world of radio!

Freq Show: Raspberry Pi RTL-SDR Scanner – [Link]

### Low Cost 10Mhz Frequency Reference

by Mark “hiddensoul

### DS3232 clock frequency calibration

Kerry Wong writes:

DS3232 is an extremely accurate RTC with a guaranteed accuracy of 2.5 ppm (0 °C to 40 °C), which translates into an error of just 80 seconds over the course of a year under the worst case scenario. I had done a few projects using this chip before (you can read about them here).
While by default DS3232 is already very accurate, we can push its accuracy even higher by adjusting its aging offset register (8bit). This adjustment works by adding or subtracting the corresponding capacitance to or from the oscillator capacitor array. The adjustable range is represented as 2′s complement (-128 to 127) and each LSB change corresponds to roughly 0.1 ppm of change in frequency. So the overall adjustment range can be achieved programmatically is roughly ±13 ppm.

[via]

DS3232 clock frequency calibration – [Link]