FPGA circuit design prerequisites

[foTONICS]

Hey all,

Just wondering. I've always been interested in FPGA design, VHDL, and programming microcontrollers with C.

I'm wondering if I have the right background to possibly do freelance FPGA work in the future. I went to school for electronics engineering technologist (3 year program). I work with microcontrollers as a hobby and have recently started to re-read through my intro VHDL textbook from school. I did pretty well in that class but wanted to know if FPGA circuit design was a computer science path or if someone with a more hands-on/hardware/electronics engineering background would have the right knowledge to pursue something like this, is it more software than hardware or a nice mix between the two?

Any thoughts, insights, or just tips on how to proceed are GREATLY appreciated.

 

[BGB]

Hey all,

Just wondering. I've always been interested in FPGA design, VHDL, and programming microcontrollers with C.

I'm wondering if I have the right background to possibly do freelance FPGA work in the future. I went to school for electronics engineering technologist (3 year program). I work with microcontrollers as a hobby and have recently started to re-read through my intro VHDL textbook from school. I did pretty well in that class but wanted to know if FPGA circuit design was a computer science path or if someone with a more hands-on/hardware/electronics engineering background would have the right knowledge to pursue something like this, is it more software than hardware or a nice mix between the two?

Any thoughts, insights, or just tips on how to proceed are GREATLY appreciated.

can't say for certain, but I think this is more in the HW/EE path.

CS tends to be a lot more concerned either with pure software, or alternatively mostly with business computing.

depending on the college, CS may focus on either things like programming languages / compilers, operating systems, ..., or alternatively things like business systems (ex: IBM System i), database administration (SQL, ...), web-programming, ..., with a side emphasis on things like finance and accounting, ...

but, yeah, the sad state of "CS" and the near absence of computing jobs I "actually find interesting" (stuff that is *not* business computing and web development) has basically caused me to largely leave computing in favor of focusing a lot more on electronics and robotics (which I personally a lot more interesting).

however, I am left a bit out of place in electronics, having not as much interest in analog signal processing nor discrete logic ICs, as this is stuff I can generally do faster/easier/cheaper using a microcontroller or microprocessor (it is more about getting signals to/from the internal control software, rather than trying to build the behavior into the electronics per-se).

most of what I have been left doing on the electronics side then has mostly been (essentially) power electronics and motor controls.

I don't really have any real experience with FPGAs, but they seem interesting at least.


and, much of what I have been building (boards-wise) has been things which could (in a conceptual sense) be trivially done using an L293 or L298... except... that these ICs pretty much explode trying to run nearly *any* of the motors I am using (generally requiring use of discrete BJTs or MOSFETs instead). but, you can do a lot with a dual H-bridge.

the size of circuits isn't so much about packing more things in a small space, so much as being able to effectively supply power, able to have enough space for adequate cooling and for the wiring.

but, yeah, there are things in electronics besides spinning motors.


but, at the same time, I would really like it if there were small-yet-powerful electric motors, say, if a 50W or 100W 3-phase motor and controller could be fit into a space similar to that of a small PMDC motor. where you connect up power, and maybe a twisted pair of wires for running control data, say, probably using a kind of serial-based star-network for controlling everything (you have a big hub that the wire pairs can connect to, maybe using spring-loaded connectors or a punch-down tool or similar, which is in turn linked up to the main controller).

for example, it isn't so easy to do a human-like robot arm (with human-like levels of grip and lifting capacity), as the motors and electronics will tend to be a bit bulky and expensive (and pneumatics starts looking a little more attractive in comparison, say, with most of the articulation being controlled with solenoid valves and air-cylinders).

 

[foTONICS]

Thanks for your response, I took a motors class in school too and found it pretty interesting. What you said about motors exploding those IC's, I have a friend in space engineering and he's constantly frying his beaglebones trying to use them to drive motors. I don't think I can count the amount of times I have lectured him about buffering his microcontroller from his motors.

 

[BGB]

Thanks for your response, I took a motors class in school too and found it pretty interesting. What you said about motors exploding those IC's, I have a friend in space engineering and he's constantly frying his beaglebones trying to use them to drive motors. I don't think I can count the amount of times I have lectured him about buffering his microcontroller from his motors.

yes. luckily, I have not fried any of my controllers (generally I am using Raspberry Pi's).
but, have blown enough transistors in my boards built to drive motors though.

tried using an L298 to run a stepper, but even the small stepper was too much for it apparently (and I was like, "screw it, going to buy some more TIP120 and TIP127 transistors and similar and just use these"...). (the continuous rating for the stepper was just below the "absolute maximum" rating for the L298, me not realizing until later that there was a bit of a problem with this...).

I have some L293 ICs, but currently can't really use them, as pretty much all my motors pull more than their maximum rated current.


recently blew up a board which had been using some 30-amp MOSFETs (about $1 each), I suspect because power got loose and inductive flyback fried everything (by raising the positive voltage rail to a high voltage, the board was seemingly self-powering briefly running everything solely off flyback current). clue that something has gone terribly wrong when transistors start turning red hot and spewing smoke and fire... (a situation apparently termed FET or "Fire Emitting Transistors").

I had built this board for spinning an alternator I had converted into a motor, but didn't proceed to high-power tests (unregulated use with lead-acid batteries) as I was having serious doubts about the ability of the board to drive said alternator and not blow up (I was using flyback diodes that were severely under-powered for the observed amperage values, stuff was getting very hot even limited to a low amperage value).


it blew up when trying to run another motor which was a split-phase AC motor I had rewired into a lower-voltage dual-phase motor. it probably wont be a (particularly) powerful motor (probably at most about 1/2 HP. I had more been hoping to be able to make a 3/4 or 1 HP 3-phase motor, but I would need a large spool of 20, 22, or 24AWG magnet wire for this).

I had it running previously when it was still a split-phase motor, but things blew up when I tried running it post-conversion (though, I have noted that after rewiring it, it seems to have a fair bit more inductive kick, shooting off much bigger and longer sparks after it was rewired, but this could just be due to it pulling a lot more amps).


I am considering making another cheaper board, probably just using some TIP120's and TIP127's, because while it wont put out much current (only about 5 amps), it is enough for a lot of the low-power testing I am doing (and they are cheaper then the MOSFETs in case they blow up).

this board would probably be a generic dual H-bridge, and would be used to generate 2 or 3 phase power (the prior board was 3-phase only, but could run a split-phase motor by connecting its coils between the 3-phase legs as kind of an ugly hack).


though, there is one obscure advantage of inverting dual-phase over triple-phase:
it can generate a higher peak-to-peak voltage, where 24 volt DC input can give a 48 volt peak-to-peak, as opposed to the 24v peak-to-peak of 3-phase.

so this works out to around 17 VAC dual-phase, and only 9 VAC for 3 phase (though 17 VAC is still possible by going between legs, and 10 VAC is possible if the common can "wobble" slightly).

this is mostly because in dual-phase, the "virtual common" can float rail-to-rail, whereas for 3 phase, it is basically anchored in place (at right around 12 volts).

in practice, the output voltage may be a little higher, since if one is running off of a few lead-acid batteries, the battery voltage (for charged up batteries) may be closer to 28 volts (so, maybe 19v and 11v for the AC output).

admittedly, I am still not entirely sure how direction control in dual-phase motors works and behaves (my ability to visualize it doesn't really show how/why an induction motor would prefer to spin in one direction or another if given straight dual-phase input, at least absent a phase-offset, say using a 60 or 75 degree phase offset rather than a 90 degrees).