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Second-hand Rubidium Frequency Standard:

Cost: $80 on eBay.

Measured:

As described by Dave Jones:

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Oh yes, and this came in the parcel, strangely enough:

A small bear and a 7805 voltage regulator.

your frequency meter looks pretty accurate too
so how do you tell if the frequency meter or the frequency standard is off?
or do you assume the standard is good and adjust the meter?

mmcp42:
your frequency meter looks pretty accurate too
so how do you tell if the frequency meter or the frequency standard is off?
or do you assume the standard is good and adjust the meter?

Yes, any calibration/validation procedure is based on some 'standard' or 'reference' you have avalible to you. The better the standard the more accurate your procedure will be. The old rule of thumb is that your standards or references need to be 10 times the accuracy specification of the thing you are attempting to calibrate.

Of all the electrical measurements possible, frequency is the one that has the best standards and accuracy avalible. That Rubidium Frequency Standard requires no adjustment, it's based on a fixed property of the wavelength of Rubidium, thus making it a very desirable frequency standard.

Lefty

Offering alternatives on ways to cope with unregulated power?

mmcp42:
your frequency meter looks pretty accurate too
so how do you tell if the frequency meter or the frequency standard is off?

Well this was interesting. I put the output from my signal generator (also nominally 10 MHz if required) into the same counter, and it gave the same results (10000.046). That's nice, I thought, my signal generator is correct. But putting both signals into the scope it was obvious they weren't the same frequency at all. In fact, compared to the Rubidium standard the signal generator kept changing (speeding up, I think), no doubt as it warmed up.

That's nice, I thought, my signal generator is correct ...

I was impressed by your frequency meter with three decimals precision. Putting it to test and finding it is less precise than expected kind of ruins your day. :relaxed:

The saying, "A man with one clock knows what time it is. A man with two clocks is never sure." seems to apply here as well.

Well that clearly demonstrate the difference between precision and accuracy.

I spent a career with instrumentation. Accuracy is one of the most misunderstood, misused, and abused word in the world of electronics. Never trust a salesman or his spec sheets. Never accept an accuracy figure or specification without knowing and asking a whole lot of questions about how they are arriving at their specification and under what conditions.

It's a very interesting field, measurements and standards, but far from as simple as one might first think.

Lefty

I got a 1m blue led strip for 1$ free shipping off ebay, buyitnow price 10$ XD
Waiting g for the day I get that 5m rgb strip with ir control for 1$ instead of 20

Was it a chinese supplier? They almost always seem to throw in wacky "extras"... :wink:

cr0sh:
Was it a chinese supplier?

Yes.

My order from Futurlec (California) arrived from China, 12 days transit not the 7-10 quoted. Somehow I got the 256k-bit serial rams as surface mount chips though the 64k-bitters are DIPs.

It's time for me to play with SPI so expect maybe some stupid questions.

100 ATMEGA328P-PU from mouser.com These will hopefully last through the summer :)Their 25 point break has got about 1% increase from my last purchase. Digi-key ran out of them.

do tell what do you do with 100 328's that will only last you through the summer? Since 2009 I have only used 2 hehe (and 3 168's and a handful of tinys)

oh and I hope you enjoy your 5 inch thick mouser catalog(s) soon to come ... they make good monitor stands

nothing really against mouser, but when you pay 1% more for 100 and you get a freaking phone book a week later you start to wonder if that 1% could have been shaved by not mailing a brick that has a 98% chance of instantly ending up in the dumpster (and its much more insulting when you buy a 1.50$ + shipping that really should have cost 2 dollars shipped sans doorstop)

edit:
against mouser I hate their search

Osgeld,

I have designed a family of serial LCD panels and backpacks with ATMEGA328P. I'm flashing them with my code and selling them in kits. My first 25 ATMEGA328P lasted 3 months, next 25 lasted 3 months. Not to use linear regression but just common sense, this 100 will last 8 months or less, the end of summer.

I wouldn't mind a catalog though. I find catalogs very useful in getting a feeling of what each part looks like. I can also take notes on the catalog. One is enough.

2x Nema17 stepper motors with 26:1 planetary gearbox on

2x N.O. temperature switches, closes at 35c

Just over four hundred one half watt .4 ohm resistors -- a dollar including shipping (no, I don't have an actual plan for em)
Twenty TIP41C and a hundred 5.1v zeners -- four dollars shipped
five three-watt warm white LED's, including constant current drivers -- Four bucks and change
USB ASP Programmer -- a dollar shipped
Twenty LM317T and ten ULN2003A -- Ten bucks shipped.

I hit a scratch ticket for twenty bucks and decided to do a bit of ebay bottom-feeding... :slight_smile:

Crimp tool...

finally had enough of using pliers that never really worked anyways