7400 frequency counter

This frequency counter is [Miguel Pedroso’s] entry in the 7400 Logic contest. After looking at the design we think this is a perfect project for those who have not worked with logic ICs before. The concept is simple and [Miguel] does a great job of explaining his implementation.

At its heart the device simply counts the oscillations of an input signal for one second, then latches the total to the 7-segment displays before zeroing the counter block and starting over. Six 4029 decade counters give the device a range of 1MHz. A set of 4511 BCD to 7-segment decoders translate the count to the display. A 4521 frequency divider chip uses an on-board 4.194304 MHz crystal oscillator to time both the display latching and the counter clearing. [Miguel] mentions that tuning the load capacitors is a bit tricky. Since breadboards have their own capacitance issues it may be necessary to change the load capacitor values when moved to protoboard or the crystal won’t start oscillating. You can see those caps are not the same value, but the tests in the video after the break show that this is pretty much spot-on.

If you’d rather give this a try in HDL here’s an FPGA-based frequency counter from which you can draw some inspiration.

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Building a 100 MHz frequency counter

The great thing about building with gates is the crazy speeds you can achieve by using hardware directly (as opposed to working with simple microcontrollers). This 100 MHz frequency counter is a great example. [Michael] just finished building it using a Papilio board.

Of course we’re not talking about discreet chips here. The Papilio is an FPGA development board which means he is building with hardware gates, but that is still done by writing code. Above, the rig is measuring a 25 MHz being generated by a second FPGA board. Using the Papilio’s on board 32 MHz clock the device is capable of counting a frequency up to 100 MHz. You can see it measuring a 96.875  MHz signal in the video after the break. One interesting thing about that clip is that near the end he touches the crystal’s case with his finger and the Hertz really jump for a moment.

If the 8-digit display looks familiar that’s because [Michael] recently published a library to use it with an FPGA.

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Adding USB connectivity to old benchtop tools

frequency_counter_hacked_for_usb_connectivity

[Scott] was recently given a frequency counter, and once he brought it home, he started contemplating how he could possibly make it better. While the counter worked well as-is, he wanted to find a way to record data readings over a reasonably long period of time. He figured that interfacing it with his computer would be the best way to do this, but he had to find a way to connect the devices first.

He started poking around inside the frequency counter and stumbled upon a possible data source when taking a closer look at the display board. He found that he could read the frequency data as it was being written to the display, and send that data to his computer. He used an ATMega48 to intercept the data and code from the V-USB project to bit-bang the data to his PC over USB.

Now, anything he sees on the frequency counter can be easily collected and graphed on his computer with little fuss.

Stick around to see a quick video demonstration of his hack in action.

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Precision frequency measurement library for 8-bit microcontrollers

[Paul] has been working on porting over Arduino libraries for use with the Teensy microcontroller platform. This tends to be pretty simple since they both use the same Atmel chip architecture. But once in a while he finds the Arduino libraries are not what they’re cracked up to be. When looking to port over a frequency measurement library he ended up writing his own that works better and is much more portable.

He had two big beefs with the Arduino Frequency Counter Library. The first is that it required the compensation factor the be calibrated using an accurate frequency counter. That’s a chick-and-egg problem since many people who build a frequency counter with an Arduino are doing so because they don’t already have a standalone tool. The second problem is that the Arduino library was hardcoded for ATmega168 or ATmega328 chips.

This new library fixes both issues with just one trade-off. Your hardware setup must be using a crystal oscillator. You can see above in the image above that the frequency measurement is quite accurate with this method. The package also uses a thin abstraction layer which will make it easy to port to any 8-bit microcontroller which is programmed in C.

PIC based frequency counter

Here’s a PIC based frequency counter that outputs the count via an RS232 serial connection. [Oakkar7] tipped us off about it after seeing the AVR based counter we featured yesterday. This project is a bit older and a bit dirtier.

Inside the metal DB9 housing you’ll find just seven parts. The most important is a PIC 16F628 which handles both the counting and the serial communications. We’re not quite sure how it’s managing to talk to that USB-to-Serial converter without some type of level conversion. Since this microcontroller is not a dedicated counter chip a little bit of trimming must be done to bring the accuracy into spec. There’s also some physical trimming involved. In order to get everything to fit into the small enclosure the circuit was free-formed without a PCB or protoboard and the case of the DIP chip had to be ground down just a bit. As for the readout, a simple script can grab the data and display it in a terminal.

[via Piclist]

Frequency counter for $10 worth of parts

[Scott] built this frequency counter using less than $10 in parts. It’s set up to meter frequencies in megahertz which is fitting since he’s planning to use it with his radio hardware experimentation. But we would find it useful too because our cheap multimeter only reads up to around 4 MHz.

He’s using an ATmega16 that he had on hand but it has features way beyond the specs for the device. He speculates that an ATtiny2313 would easily work in its place. The microcontroller is mostly used to drive the multiplexed 7-segment display after reading the frequency values from the 74LV8154 counter chip that he is using. He doesn’t have a full schematic for the device, but there is a hand drawn diagram for using the frequency counter; the rest should be easy to piece together. Looking at that circuit we don’t think it would be too hard to make this a manual-ranging frequency counter to give you more use out of the dedicated device. Check out [Scott’s] demonstration video which is embedded below the fold.

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Nixie frequency counter gone timepiece

nixie clock hack

[Windell] of Evil Mad Scientist Laboratories took an ancient Nixie tube based frequency counter and converted it into a clock. The unit he got his hands on is an HP model that was still in great shape. He’s using an internally generated one second pulse as the clock signal, but some modifications are necessary to display time. That’s because the frequency counter is base 10 and clocks use a quirky combination of base 60 and base 12.

It wasn’t too much of a problem to rig up a system to track minutes and seconds. The tens digit for each is monitored by a couple of AND gates that he added to the mix. When they detect a ‘6’ the digit is reset and a pulse increments the next digit as the carry. This is more difficult to accomplish with the hours though. Minutes and seconds count from 0 to 59 but hours don’t start at 0. Instead of over-complicating the logic [Windell] used a bit of slight-of-hand. The Nixie tubes for the hours have been rewired so that when the counter is at 0, the filament in the shape of a 1 lights up. No difference in logic, just a translation that makes them display one digit higher than the actual count.