Re: FS-4B (with frequency counter)
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Hi Garry
Why doesn't your solution use an external clock oscillator with a 16mHz OCXO like this
features are
Specification: Operating voltage: + 5V dc / +/- 5% Operating current: 20mA (MAX) Output waveform: TTL/CMOS Duty Cycle: 40/60% Frequency Stability Vs Temp: +/- 0.2ppm (-10~+60C) Size: 20.8x13.2x15mm Aging: +/- 0.1ppm/year. Input voltage: DC6V-10V
73 Gilles
 Gilles F1BFU since 1969GQRPClub 15889?QRP ARCI 16979
??Le vieux monde se meurt, le nouveau monde tarde ¨¤ appara?tre et dans ce clair-obscur surgissent les monstres¡??? Antonio Gramsci (1891-1937)
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I started a new thread based on a comment by Gilles on Doug's talking FS-4A thread.
YES, the frequency counter in my FS-4B is less than desirable.? This is due to the ceramic resonator that is the time base on the cheap Arduino Nano boards.
The resonator has quite a warm up drift but after its temperature is fully warmed, it is "pretty" stable.? Since a counter needs a stable gate signal, this is a problem.
I found that you can provide an external clock signal to the Nano board rather simply.? See attached photo.
If you lift the two ATMega pins on the corner and solder a fine jumper to the second pin, you can supply an external 16MHz clock without an changes to the fuses
or Arduino code.? 0-3.3V or 0-5V squarewave is what you want to apply.? To get accurate frequency counting, it needs to be exactly 16.0000MHz and stable.
I was able to find a small $3.50USD clock chip at Mouser with temp compensation AND a voltage controlled freq trim pin.? Unfortunately they don't have these anymore
and I haven't been able to find them anywhere else.? You could make your own with a crystal and a trimmer cap... maybe use a logic gate oscillator or a transistor?
Maybe you can bring out two jumpers and get the ATMega into crystal oscillator mode by itself?
My workaround was a "calibrate" mode in the FS-5B code.. not ideal but after warmup it works pretty well.
I have also been looking for? a substitute for the Nano.? I thought I found it in the STM32 boards which have a crystal, are very advanced over the ATMega but?
unfortunately their software includes the FreeRTOS real time operating system with random interrupts to look for task switching.? The frequency counter works
great most of the time until the random interrupt corrupts... bummer.? Nobody seems to know how to shut down the RTOS... especially me.
NOTE: the Nano did have a similar problem with the millisecond counter interrupting but I did figure out how to stop that during freq counts.
If anyone knows a good cheap little computer board like the Nano but with a crystal and available freq counter code, let me know.
My FS-5 in both my R-4B (frankenstein!) and T-4XB have great stable counters using Nanos, so it is possible.
73,
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