Author Topic: 3 Dollar Precision Frequency Standard (Read 33207 times)

paulie · « **Reply #25 on:** April 24, 2015, 11:48:45 pm »

Quote from: Alex Eisenhut on April 20, 2015, 10:12:20 pm

Did someone say three dollars?

LOL, almost missed this one.

I am constantly amused at the expensive and complicated Rube Goldberg setups that some hobbyists and even professionals cook up. Partly a result of sino-phobia which is pandemic in these forums and partly a strange obligation to just throw money around (Lamborghini Syndrome). Sometimes reinventing the wheel makes sense. For example education or entertainment (building is fun) but unfortunately that is not always the case.

There's only one thing better than solving a problem with a $3 Ebay trinket and that's solving it with a $1 trinket.

paulie · « **Reply #26 on:** April 26, 2015, 12:49:10 pm »

A friend noticed couple entries in the page one table were off so I fixed that and uploaded the program used to generate divisions along with details on use. If there are any questions don't hesitate.

paulie · « **Reply #27 on:** May 12, 2015, 05:39:27 pm »

Exactly one month after last calibration I thought another checkup might be in order. This time only the frequency standard was tested against WWV and was about 2 Hz off. Interestingly 2 under whereas last time it was 1-2 over so this may be indication those Raltron TCXO are pretty good for long term drift. Room temperature is about 10C higher now but I don't know if that has much effect.

Other news... on request from a couple local pals I updated the code to run on Mega328 and button pushes are easier. Instead of dividing once per hit it skips directly through the table frequencies on page one. If anybody here wants to build this version let me know and I'll put up files. Wiring diagram is the same as for the Mega8.

netdudeuk · « **Reply #28 on:** May 12, 2015, 10:01:41 pm »

Great thanks. Please will you upload the 328 stuff.

I ordered an ATMEGA8 a while ago and am still waiting. I have several 328s.

I've also got a couple of these 10MHz Vectons so I'm raring to go.

Thanks

Flump · « **Reply #29 on:** May 12, 2015, 11:28:24 pm »

could this be done with an arduino ?as i have a spare uno and i have a 10mhz ocxo
would love to have 5mhz and 1mhz at the push of a button

netdudeuk · « **Reply #30 on:** May 13, 2015, 07:10:50 am »

The Uno uses a 328 so that's now supported but I expect that you'd need to lose the boot loader and then it wouldn't really be an Arduino any more. However, those chips are about a £1 from China and you could probably use the Arduino to program it.

paulie · « **Reply #31 on:** May 13, 2015, 11:39:35 pm »

No need to over-write the bootloader. Hex files can be downloaded with avrdude using serial interface just like any Arduino program. In fact one of the fellows here is using a Pro Mini board and he can still use it for loading Arduino programs when not being used as a frequency reference. It is only necessary to tell the compiler a 20mhz clock is used instead of the original 16mhz. This is done by way of a new entry in boards.txt file.

Hardware modifications to that tiny module were the only tricky part and that wasn't too difficult really. Just a little fine soldering work to reroute the clock to the TCXO which was HUGE compared to the original SMD ceramic resonator. The clock accuracy is like a million times more accurate and precise now. He tells me when running a calendar clock ino file it loses less than two seconds a week.

Modifying a Uno should be much easier with it's full size crystal. Too bad Arduino designers didn't think to bring out the B6/B7 pins which would eliminate the need for any modifications at all. One of the few gripes I have with using these boards whether it be Arduino or non-Arduino assembler, BASIC, or C.

Anyway I will dig up the m328 file and post when I get a minute. Putting out some work related fires ATM.

paulie · « **Reply #32 on:** May 14, 2015, 12:51:26 pm »

Mega328 file uploaded to first post along with implementation details. Dozens of individuals have worked with the Mega8 version but only a couple guys besides myself with the new one so not as well tested. If anybody finds bugs or even if it works OK it would be appreciated to post your experience.

paulie · « **Reply #33 on:** May 22, 2015, 01:24:16 pm »

Due to personal need for more convenient access to useful frequencies I modified the original program to include several additional "quick skip" entries. Details in first post.

netdudeuk · « **Reply #34 on:** June 28, 2015, 10:00:47 am »

Paulie, I've come to build this project today and notice from the first post that I recently bought the same frequency counter as you.

I'm really pleased with it (although did get caught out by the fact that the red and black are the wrong way round on the keyed source connector) but the display is far too bright.

Do you (or anyone else) know which of the three variable pots is used to control the display brightness ?

I'm guessing the one in the diagram but would prefer not to just give it a go.

jdraughn · « **Reply #35 on:** June 30, 2015, 01:12:03 pm »

It would increase the cost drastically, but a rotary encoder with push button switch could make a awesome little upgrade.

netdudeuk · « **Reply #36 on:** June 30, 2015, 03:18:36 pm »

Well, 99p posted for the encoder isn't too bad and even less for the switch.

Let him know when you've written the extra code

mtdoc · « **Reply #37 on:** July 01, 2015, 03:27:51 am »

I bought a set of these today. This looks like a fun project and it will give me an excuse to learn how to use AVRdude which I've been meaning to do for a while.

netdudeuk · « **Reply #38 on:** July 05, 2015, 05:49:07 pm »

I finally got round to building one of these today using an M8, the Vectron 10MHz TCXO and the frqpb806.hex firmware.

I connected it to my DS1054Z and a frequency counter like that used by the OP.

Starting off at 5 MHz, the scope shows that and so does the frequency counter, fluctuating by only 1 Hz.

Stepping down, when I get to 625 KHz on the scope, the frequency counter actually shows the second harmonic (1.875 MHz). Stepping down again and again continues to show the second harmonics on the frequency counter.

Why do I start to see the second harmonics on the frequency counter ?

Any way round this ?

Thanks

mtdoc · « **Reply #39 on:** July 10, 2015, 05:35:34 pm »

Got this working on the breadboard last night. Had to remove the crystal on the Arduino Pro Mini and solder a wire to access the XTAL1 pin which is not broken out on the Pro Mini. Now I just need to put it in a box. I'm still considering whether to use a battery or a power jack. One nice thing about the Pro Mini is it will take unregulated power input.

Thanks to the OP for a fun project

mtdoc · « **Reply #40 on:** July 14, 2015, 06:20:25 pm »

Put this in a box last night. Now I have a cheap sanity check frequency standard. Yeah! Thanks Paulie for the idea.

neslekkim · « **Reply #41 on:** July 27, 2015, 05:57:03 pm »

Quote from: mtdoc on July 01, 2015, 03:27:51 am

I bought a set of these today. This looks like a fun project and it will give me an excuse to learn how to use AVRdude which I've been meaning to do for a while.

Hm, those tcxo's seems cheap, but the seller uses GSP

, $29.34 for shipping..

neslekkim · « **Reply #42 on:** July 27, 2015, 06:03:22 pm »

Do anyone have a link to this frequency counter?, found some on ebay, but most are pic based?

netdudeuk · « **Reply #43 on:** July 27, 2015, 08:23:28 pm »

There are loads of them on eBay. However, there seems to be a problem with my 2.4GHz version where once the output of the TCXO gets down to a certain frequency, the counter always shows the second harmonic and not the actual frequency, even though my scope shows the correct value.

I've posted about this earlier in this thread but no one has suggested possible causes or solutions for this. I'd still welcome input from those more experienced, please.

neslekkim · « **Reply #44 on:** July 27, 2015, 10:01:06 pm »

yes, there are loads, mostly pic based, and I wonder if the claims are unrealistic, for instance:

up to 1.1ghz:
http://www.ebay.com/itm/181662710870
up to 2.4ghz:
http://www.ebay.com/itm/181806842808

etc..

netdudeuk · « **Reply #45 on:** July 28, 2015, 06:26:37 am »

That's the one that I have. Is there really no one on one on the EEVBLOG forum who can answer the harmonics question?

netdudeuk · « **Reply #46 on:** August 09, 2015, 11:22:56 am »

Hi guys

Still not having much joy with this project.

I have this TCXO -

http://www.ebay.co.uk/itm/Vectron-10MHz-TCXO-SMD-5V-2-5ppm-30C-75C-T1115-10M000000-Qty-2-/160999666268?pt=LH_DefaultDomain_0&hash=item257c53f25c

It is running from a DP832 at 5v with the output going only to my 1054Z.

According to the scope, the frequency constantly fluctuates and is always somewhere between 9.61 MHz and 10.1 MHz.

Any idea why the output signal seems to be so far out of spec ?

Thanks

TerminalJack505 · « **Reply #47 on:** August 09, 2015, 03:15:26 pm »

Quote from: netdudeuk on August 09, 2015, 11:22:56 am

Hi guys

Still not having much joy with this project.

I have this TCXO -

http://www.ebay.co.uk/itm/Vectron-10MHz-TCXO-SMD-5V-2-5ppm-30C-75C-T1115-10M000000-Qty-2-/160999666268?pt=LH_DefaultDomain_0&hash=item257c53f25c

It is running from a DP832 at 5v with the output going only to my 1054Z.

According to the scope, the frequency constantly fluctuates and is always somewhere between 9.61 MHz and 10.1 MHz.

Any idea why the output signal seems to be so far out of spec ?

Thanks

Are you using the scope's hardware counter? Or the software counter?

Sounds like you might be using the software counter.

netdudeuk · « **Reply #48 on:** August 09, 2015, 05:58:11 pm »

Ah ha ! So I was thanks.

Enabling the counter in Measure > Counter gives me a very steady 10.0000MHz.

Why would the frequency counter at the bottom of the screen be so flaky though ?

Also, as you're on a winning streak so far, maybe you would also be able to answer my questions up above regarding me using a frequency counter with this circuit and only seeing the 2nd harmonic frequency ?

Thanks

TerminalJack505 · « **Reply #49 on:** August 09, 2015, 06:41:45 pm »

From what I understand, the frequency measurement at the bottom of the screen bases its measurement on the captured waveforms. This is done in software so, as a tradeoff between speed and accuracy, they cut some corners in their calculation. (They likely don't account for partial cycles.)

So far as your other problem goes, I can't say. It might be helpful if you posted the waveform. Maybe there's something about the waveform that is confusing the frequency counter.


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Author Topic: 3 Dollar Precision Frequency Standard (Read 33207 times)

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