Fast ADC simultaneous readings

Hi Gabriel,

The Tiva fastest ADC can only measure at 2Mhz, and in the setup you want, its only 1Mhz. 15 Mhz is a hell of a speed for analog readings with a MCU.
The Tiva you refer can only reach 1Mhz max, and in your setup the maximum is 500kHz - the ADC itself works at 16Mhz!

I would go to a dedicated ADC for that. But you really have to be careful with 15Mhz readings - it needs lots of hardware considerations (impedances, so the capacitance, resistance and inductance of the components and board). Noise will also be a problem meaning you can lose a lot of precision.
You have this one, the ADC1173, which has 8 bit resolution, with 7 or 6 (or 7.6?) effective bits (at least promised) and can go up to 15MSPS. It uses parallel communication so you can use it with bit-banging (others I've seen at those speeds were parallel too so higher resolution is more tricky). You would need 2 since each has only 1 ch.

If you really need the 15Mhz double sample readings I advise you to get help from a electrical engineer in your zone. It will be tricky getting everything right. Anyone here more experienced in the matter correct me if I am wrong.
If you want to just use the dual 500Khz maximum of the Tiva then you of course need to check inductance and noise.

Hi Luís
Thank you on a reply.
If i would like to use 500 kHz inputs how can I do that?
I am not so good with writing a code as you can see, so I could really use your help.
Regards

Some way/how I recall either this same post (or one amazingly similar) having (past) landed here.    (months, maybe half year or so, ago)   

We must note the inconsistency in your writings:

• opening post specifies 15MHz sampling rate
• next post "relaxes" to 500KHz

That's a 30:1 change - can both (or any) be correct/proper?

Luis suggested your collaboration w/one skilled in this area (EE) - ideally w/in your locality (school, firm) so that he/she may supervise your implementation & be available for the inevitable technical: questions, changes, verifications...

Such project seems ideal for this/other vendor's Analog Eval boards (two) which may be "synchronized" so that the conversions have (some) chance of being (near) "simultaneous."

I need more likes for this!

For the OP I would, considering his environment, I would urge you to strongly consider a digital storage oscilloscope with USB storage. Let someone else do the electronics so you can concentrate on the data analysis. This is far from the leading edge for DSOs.

Robert

Robert Adsett72 said:

I need more likes for this! 

Monsieur - just "what" are we to "like?"   (note that Luis has (already) secured 3!  (you/I/o.p.))

Scope "shines" if the requirement is (not) on-going.    Persistent scope presence likely, "breaks poster's bank."

You can get 'scopes in this speed class for quite a bit less than $1000 now and good name brand ones for not much more than $1000. I realize 'grad students are free' but even still.

Reviewing the original post though I'm wondering if a lock-in amplifier might be a better solution. Cost is likely to be an issue for that though.

Robert

I still wonder about the (long disappeared) "real" o.p. - who made near identical forum request...

Different student?

Robert

AFAIIK, fluorophore is not really a common household chemical, so the OP might have access to a proper university lab. That suggests that he or his mentor can organize a proper scope.

And if not, even cheap scopes today come with a FFT feature. I have a 2-channel Rigol with 100MHz bandwidth for about 700 Euros (albeit this FFT feature is somehow arcane).

As an alternative, I know of several vendors for PC interface cards that support such sampling frequencies (>15MHz) for analogue signals. Even if not really cheap, a university is supposed to have something like this, most probably including LabView drivers ...

Maybe walk over to the physics department. It would be a more common piece of lab gear there and you might even find one in an upper level undergraduate lab.

If that's the same 'scope I'm thinking of it's even less expensive in North America.

Robert

If that's the same 'scope I'm thinking of it's even less expensive in North America.

Perhaps. I bought it more than 3 years ago, when I needed one. And like always, the price started to drop soon afterwards...

Well, no reason to be vexed. It still does the job. And, AFAIK, Rigol previously manufactured for Agilent, so I don't expect reliability issues.

f. m. said:

And like always, the price started to drop soon afterwards...

So true - one assumes your "Hot stock tips" fare better...   (to diversify - I've a "bridge in Brooklyn...")

With all due respect
I see a lot of replays but not single one helpful.
As i said I am an chemist, and I have a proper lab, and all needed equipment for mine research. I was simply wondering is it possible to measure two incoming signals with Tiva for reasons I don't want to repeat.
I possess the equipment to measure lifetime on 1ns scale, and it is very expensive.
I am new in electronics and this is mine first project.
As Luis Afonso so nicely explained it is not possible to obtain 15 MHz ( which I would need to cover all !! lifetimes of mine dyes/fluorophores),
but even 500kHz will suffice for few of them !! . and that is why I "relaxed" to 500KHz (as ch1 is said so ).
Mine goal is to make device (cheap and easy to use) capable of measuring lifetime of fluorophore (and for that even 500 kHz will do).
If there is someone who knows how to write code for tiva, so i can measure and collect data points simultaneously on both ADC with "speed" of 500 kHz (electronics including photodiode, amplifiers and everything is done), and is willing to help me please contact me, or post it in replay.
Thank you.