When looking at a schematic of an analog to digital converter, I see 14 digital outputs rather than just one, how do I connect this to an arduino or any board? How do I get this output word?
If you have to know the background story:
this is the ADC I'd like to use because of its high sampling rate you'll find this "output word" i'm talking about on page 24 in Fig. 36
and this is the "D flip flop" IC
the higher sampling rate the better, it will take voltmeter converted reading of ammeter reading of photomultiplier tube's circuit so that I can read the amount of secondary electrons on the sample as a beam sweeps across a specimen
The output word is spread across all the 14 D0..D13 pins. So connect each pin to 1 arduino input pin. On UNO etc that will use almost all the pins. Use a mega? When you want the voltage word the way to do it with the normal Arduino programming would be to read each with digitalRead (all 14!) and assemble the input word by 'or'ing the bits. It would work, but look clumsy, and might be too slow. Computers I've used in the past have methods of reading the whole word in 1 go. I don't have a Mega, maybe it has this. Try following the digitalRead code down into the libraries, see what it actually does underneath, and make your own call that reads all 14 pins.
If you read the data in parallel form then study the port assignments of the Mega. With proper pin connections, you can get all the data with two port reads. Find a pin assignment map for further details.
Also, you can connect the ADC pins to a pair of shift registers and get the data using only two pins into any Arduino.
Option #1 is a better choice but you will need to move to the Mega2560.
PS
Here is the pinmap for the Mega. You can use all of port C and part of port A.
Or a '1284P based board, has 4 complete 8-bit ports as well.
PortD has the serial interface, PortB has the SPI interface, so use A and C with control signals as needed from B or D:
upperByte = PORTA;
lowerByte = PORTC;
int combined = (upperByte <<8) + lowerByte;
That's the scheme I was thinking of for the 2560. Never looked at, or possessed, the 1284 so not familiar with the port arrangement. Many users are not aware of the direct port manipulation. The OP should have some good ideas to work with now.
The Teensy has two new functions, digital(Read or Write)Fast(). It appears to be doing something along the same lines. Are you familiar with the inner workings of these two functions?
Wow this is exactly what I needed, thanks guys. As far as teensy goes, Im not familiar with those functions but have a teensy LC. I have an UNO and a DUE and a latest raspberry pi 3B is on the way, I wonder if any of these boards can do it already
The direct port manipulation can be accomplished on any Arduino as long as you know their names, AFAIK. Look for an example on how to set high, set low, and read pins as the structure is a little different.
Only the Teensy 3.1 and 3.2 have dual ADCs. They can be triggered in sync using the special ADC library. My tests show a maximum sampling rate of about 62.5Ksps. I used a timer which generated an interrupt causing the ADCs to read and store. The routine worked correctly when the timer was set for 16usec or longer. At 15 and below, it tried to sample again before completion of the previous read. There are probably ways to make it faster but it will work OK in my project.
The Teensy data can be found here.
Not familiar with the Pi so can't comment on that one.
Your ADC chip could be used in mulitples and triggered with a common line. However, your sampling rate will depend on how fast you can read each and store. If there are not enough ports on the Arduino for all channels then you will have to access each ADC with data selector or tri-state buffer chip(s).
PS
Is this part of a scanning electron microscope project? I dealt with that kind of equipment for 28 years during part of my career in a nuclear weapons manufacturing plant.
Yes it is for a scanning electron microscope, fascinating machines arent they. Would love to to do some lithography and nanotechnology with it. I have another thread on here that discusses the beam deflection via an arduino DUE's DAC. I learned a lot from applied science's vids on youtube where the guy makes his own.
Are you saying that after the analog data is converted by my external ADC that an ADC inside the board has to do the writing of the values to my computer?
Only one conversion is needed in your external ADC. It presents the data on the 14 pins and the Arduino only has to read those pins using the port read feature. It will still take some amount of time to run a loop strobing the ADC, looking for data ready, and read it in to an array. You can test that time by using Robbin2's example for port read with indexed array storage inside of a for loop for maybe 10K times. Read micro() before and after the for loop and calculate the read/store per second time.
What photo multiplier are you using, Dumont perhaps? Are you familiar with the Channeltrons from Bendix? They are much smaller and have higher gain and lower operating voltge. We used them in a leak tester by counting atoms and got down to 1e-14 Torr.
Also, do you have the link to your other post? I operated and maintained an Electron Microprobe Analyzer for 13 years and constantly fought beam deflection problems. I also helped maintain an SEM across the hall in the Met Lab. You can send the info via PM as this is off topic.
Here is the link to the other thread,
please excuse my stupid questions as I'm currently learning the electronics of the system. I hadn't heard of channeltrons but have seen electron mulitpliers online if that's the same thing, my photomultiplier is an R1166-10, I didn't know which one to get but hamamatsu's catalog had this one listed under the same category as miscellaneous and electron microscopes
I have a varian starcell UHV pump that can start at 1e-2 torr so my varian diffusion pump is on ebay for sale, wish I had come across the UHV pump before it.