cjones

Finding the right hardware for specific job

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I'm laying out a project for work. I want to get an idea for the most stable solution with respect to hardware.

The most important aspect is reliability. A lot of very expensive equipment might get damaged if things go south.

Nobody is going to be on the hook for any recommendations as I have to approve the final design and I will do my due diligence and be the sole architect.

The Project

RF control and tuning for a cyclotron.

I've already designed the RF system and it will have 3 three tuners which are each operated by linear actuators. It will also have three RF pick-ups for measuring the RF voltage for each tuned section.

Each of the tuned sections can have its own resonant frequency but I they have to match and it has to be at a particular frequency.

The Solution

Three SISO PID controllers which will read the pick-up voltage and adjust the linear actuator.

The set points and voltages will be controlled and displayed from a top level control system. So there will be communication, likely ethernet.

Above all I want to figure out what hardware will be the most reliable.

The tuning will not occur immediately as the RF system will need time to warm up the resonator and let the frequency settle, so I will make a state machine that can automatically go through the startup process of which the tuning state will be one of portion, the run state.

Conclusion

There's quite a lot to the project and many things are already in place, but there here are a couple things I'm hoping to learn about.

  1. I think an FPGA would be best for the state machine, is it best stand-alone or is there a microprocessor/FPGA combo that would be better?
  2. Messaging will have to be sent with error detecting / correcting codes so I would like to do this with an microprocessor but given the options in question 1, is that necessary?
  3. Any general comments will be greatly appreciated.
  4. If you have any more questions about the project which would help you, just let me know.

 

I've had a fair amount of experience with the MX4 and the NEXYS2 and a host of other Digilent products so I thought this would be a good place to solicit some advice. Also, it would be a good resource for me during the development process.

 

Thanks in advance!

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Some random thoughts:

- I don't see why you'd use an FPGA in the first place. From a marketing point-of-view, an industrial-grade Zynq may be the perfect platform, but the learning effort is much higher than for a run-of-the-mill microcontroller.

- if you have no or only superficial FPGA design experience, don't use an FPGA. If you can't decide, pick any rubber duck of your choice and explain it the concept of metastability in a few sentences. Is your explanation concise and rock-solid? If not, don't consider FPGA. If you have gaps in your understanding (e.g. the design is missing constraints), every synthesis round gives you a new roll of the dice for possible failures.

- taking a shot in the dark: The most likely point of failure of any board you pick from this site is USB connectivity (probably does not matter). The next one is the voltage regulators. You can probably manage this risk (your design is unlikely to need much power in the first place, confirm by measurement and check that the FPGA runs cool). Still, looking at (expensive) industrial FPGA modules, the regulators take a lot of board space, for a reason.

- if I had to pick a module from my own experience, I'd look at LPC1768 "MBED". It is very old still not exactly cheap, manufactured in large quantities and I'd guess they have ironed out the bugs by now (on-board Ethernet, just connect a socket with magnetics).

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