3 Dollar Precision Frequency Standard

[Howardlong]

The counter is derived in hardware directly from the trigger input, whereas the other measurement is derived from the quantised information that's shown on the display, and all the inaccuracies that brings. If you stretch the waveform out while still running, it becomes more accurate, but it will never be anywhere near as good as the hardware counter.

[netdudeuk]

It might be helpful if you posted the waveform.  Maybe there's something about the waveform that is confusing the frequency counter.

As suggested.  The .TXT file cab be renamed to .CSV and then loads straight into Excel.

This is where 625KHz is shown on the scope and the frequency counter shows 1.87MHz.

Maybe someone can see the issue ?

Thanks

[uChip]

Hi,
This looked like a fun project, so I thought I would build one of these frequency standards for myself.  But I'm not very good at the dead bug style assembly shown in the thread.  Plus, I find laying out circuit boards to be sort of therapeutic.  I ordered up a few of the TCXOs and started a layout.

Never one to leave well enough alone, I thought I would add a small display so that you can see what frequency you have selected.  If you are going to hook this to a frequency counter the display is kind of superfluous, but I don't even have a separate frequency counter yet, so the display helps.

Also, someone asked for a rotary encoder for input instead of a button.  I thought that would be easier too so I added that as well.  It makes selecting the frequency a little easier.  The encoder also has a button, so I use that to switch between the table values and the numerical divisor.  Since the encoder makes selecting the frequencies a little easier, I added a few more common (even) values to the table.  And since in divisor mode spinning the knob all the way to 65000 is a pain, I made it so when you switch to divisor mode it jumps to whatever divisor the table mode was last pointing at.

A lot of times you will want to use this with a battery, but batteries have a habit of going dead, so I added a battery monitor that shows when the battery is getting low.

Finally, since there is a microcontroller in there anyway, I decided to make it remotely controllable as well.  There's an FTDI port that you can drive from a USB converter to send commands to set frequency and change modes.  The commands are all strings so you can drive it from any terminal emulator.

Here is a photo of the thing in operation,


a close up of the board,


and a screen shot of the output.


And since sharing is what the forum is all about, you can find all the design files, source files and documentation here: https://github.com/uChip/FrequencyReference .  I've shared out the board on OSH Park so you can purchase without resubmitting the design if you like.  Details are on github.

Did I get carried away?  Oh yeah, big time.  But it was fun and I learned a couple of things.  I totally blew the 3 USD budget, but it's still less than 22 USD total.

Thanks Paulie!
  - Chip

[fatboy77]

Hi paulie, I want to say to you many thanks for sharing this project!  My question is i saw somewhere you could build some boxes for sale and i am interested for one of them. Please let me know if it's possible.  Thank you, have a nice evening/day!

[splin]

With luck you'll get a helpful response - but note that you are posting to a 5 year old thread...

[WattsThat]

Paulie was banned...

Based on uChip’s design above, you could build you own. Two downsides that I see, one is that you’ve got to buy 3 boards minimum when you use oshPark and two, the 4 digit hp led bubble displays are now unobtainium.