Re: Microprocessor and RAM for a 40 MSPS data logger?


Claus, when you say that "I plan to do this by measuring and logging the
voltage across a shunt resistor, 0.01 ohms or similar" do you mean that
you plan to place the 0.01 ohm resistor directly in parallel with the
1.5 ohm resistor?

If so, you might as well throw the 1.5 ohm out as the total resistance
of resistors in parallel is less than the lowest resistance, in your
case less than 0.01 ohms (1/Rt = 1/R1 + 1/R2 + 1/R3 + etc. where Rt is
the total resistance of a parallel network consisting of resistor R1,
R2, R3, etc..)

No, my plan was to place the 0.01 ohm resistor in series with the 1.5
ohm resistor, and then measure the voltage across the 0.01 ohm
resistor. This would enable me to measure the current through the
resistors.

If you are doing 40 megasamples per second, 1024 samples would be
roughly one tenth of a millisecond of sampling, so transfer to your
computer would have to occur very very fast i.e. serially transfer 1024
samples each of twelve bits before the next sample is taken 0.025
microseconds later.

My idea was actually to save the measurements in memory and then
transfer the data to computer at a later time. By doing it this way,
the link to the computer can be very slow. It doesn't matter.

What I was hoping to find out is what type of microcontroller (and
external memory, if the microprocessor doesn't have enough built-in
memory to store the samples) that would be suitable for the job (if
any)?

Sorry I'm so negative, but I think you will have to spent quiet a few
bucks to do what you want...maybe the storage CRO would end up cheaper.


I was hoping that it could be done with simple and cheap methods.
Basically what I want is just to sample a voltage and save it to
memory. But it might not be that simple after all. There's probably a
reson as to why digitizers and storage oscilloscopes are so expensive.

Regards, Claus
.

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