Total newb, seeking advice on circuit design - Page 1
Forum section: electronics / beginners

author: STCC
author_rank: Contributor
timestamp: May 04, 2012, 06:14:38 am
content: Hi,I am moving into a new job that will involve PCB design of communication devices for industrial field equipment to interface with PLCs.This is probably only a smaller part of the job as most customers will be happy with off the shelf equipment but they have made a point that this will be part of the job.Problem is that i know very little about electronics and nothing about circuit design. I know that they want me to use a program called Altium for the circuit design and that i would need to make CAD files as well.I have acquired a copy of Altium and CAD Electrical, and also purchased an Arudino Uno some other equipment with the intention of making some simple projects and drawing them in Altium and CAD.I am not sure if i am going about this the right way and thought i'd ask this forum what you would think is the best way for me to learn circuit design and Altium/CAD and perhaps recommend a project or tutorial to do.

author: Psi
author_rank: Super Contributor
timestamp: May 04, 2012, 06:47:13 am
content: Sounds like a plan. Just be aware that an Arduino/microcontrollers programming is different to PLC programming.IMHO, they can't really expect someone with very little electronic knowledge to do professional PCB and circuit design without training.But if they're going to pay lots and the designs needed are simple then

author: slateraptor
author_rank: Frequent Contributor
timestamp: May 04, 2012, 03:14:26 pm
content: I can't help but feel a bit disturbed by the OP's predicament. Wouldn't that make you...how to put this nicely...unqualified for the position?

author: STCC
author_rank: Contributor
timestamp: May 04, 2012, 10:30:32 pm
content: Yeah, i would be, but at some point you have to bite the bullet and get out of your comfort zone if you want to progress.The majority or the work i'm perfectly qualified for otherwise they wouldn't have wanted to employ me over all the others that applied.

author: vxp036000
author_rank: Regular Contributor
timestamp: May 05, 2012, 01:39:07 am
content: Do yourself a favor and don't take the job. You'll only make yourself look bad in the eyes of your customer when something goes wrong. There's a lot more to this design than you think, and your customer should not be the guinea pig for an electronics designer that doesn't know what he is doing. Take another contract in an area that you're familiar with, and practice your own electronics designs in free time. That way you're better prepared and don't piss off your customer.

author: STCC
author_rank: Contributor
timestamp: May 05, 2012, 03:47:23 am
content: I can understand where you're coming from but to say that i need this job would be a big understatement. I will make sure the employer fully understands my my level of knowledge next interview.

author: Kremmen
author_rank: Super Contributor
timestamp: May 05, 2012, 06:01:18 am
content: A man has to do what a man has to do.Still, reading your original post i, like the others i guess, got the impression that you in fact know zip about electronic design. If you get the post i am not sure you will keep it if your future employer has any real expectations in that area. With minimal knowledge and no experience you will be able to do nothing, nada. Like try winning a match of chess against a grand master when you never played before, have no idea how the pieces move and never studied a guide of tactics. A winner? not likely... Would you enter a chess tournament? Same thing here.In my opinion your only option is to somehow delete that part from the job description. Or get your future employer to enroll you on a crash training course, if such exist. Or take another job. What you are now suggesting is just not realistic.

author: deephaven
author_rank: Frequent Contributor
timestamp: May 05, 2012, 09:44:02 am
content: The best policy is always tell the truth. Tell your employer exactly what your strengths are and also what areas you are not familiar with. Tell them that you are very willing to learn these new skills but point out that you're starting from scratch. There is no substitute for experience and that can only come with time. Don't try to 'blag' it, it just won't work.

author: STCC
author_rank: Contributor
timestamp: May 05, 2012, 10:54:24 am
content: Thanks a lot for the advice. I had already told them the last time i done any sort of electronics was a long time ago and it wasn't something i had even though about seriously since. But it seemed like all they heard was "i did electronics subjects at uni". I have an interview with them coming up and i will lay the cards on the table so to speak in relation to my current skill/knowledge with circuit design. If they still want want me great, if not too bad. Maybe i've been kidding myself about learning this so fast.Regardless i'm hooked on electronics now, and everything will work out in the end

author: whitneyrm
author_rank: Newbie
timestamp: May 06, 2012, 12:02:45 am
content: Sometimes the best policy may be to lie a little.In 1963 I got a degree in Electrical Engineering, the electronic content being zilch. Around 1968 I was working at a computer manufacturer, with some exposure to linear power supply design. I understood how a transistor worked but other than that my knowledge of electronics was pathetic. Bored with a job that was going nowhere I replied to an advert from an Aerospace company looking for an engineer to design Satellite Power Supply systems.Why not?I expected the interview to be a very short one. After the usual pleasantries the interviewer spread out a schematic the size of a dinner table.Interviewer: "Tell me what you think of this".All I could see was a baffling collection of components. The choices were either to start crying, or bluff it out.Me: "This is really interesting, I see you are using JFet's". (I recognized the JFet symbol, but had no idea how they worked).Interviewer: "Do you understand all this"Me: "Of course"Interviewer: "Good, because I don't"I got the job and managed to stay two steps ahead of being fired. I designed the sunlight power systems for two satellites.http://heasarc.nasa.gov/docs/heasarc/missions/td-1a.htmlhttp://en.wikipedia.org/wiki/Orbital_Test_SatelliteEverything worked out in the end.

author: Rerouter
author_rank: Super Contributor
timestamp: May 06, 2012, 12:15:43 am
content: whitney, you just confirmed oh so many of my thoughts :/ that there are people floating around with only the slightest understanding,while i'm sure you got better, still helps me to understand the quality of design that goes into some things, (things that werent cost cutting, but inefficient design)

author: baljemmett
author_rank: Unknown
timestamp: May 06, 2012, 12:20:42 am
content: Quote from: whitneyrm on May 06, 2012, 12:02:45 amThat reminds me ofan anecdote fromSurely You're Joking, Mr. Feynman!... So you're in good company there!

author: sonicj
author_rank: Frequent Contributor
timestamp: May 06, 2012, 05:47:55 am
content: IMO, you are going about it the right way... I think the Arduino is a lot like PLC, just minus a layer of abstraction. Interfacing the physical world with your Arduino based projects should be very similar to what a customer might require in a custom PLC interface. It doesn't sound like they are expecting you to design & layout highspeed data busses, PFC power supplies or complicated analog circuits... More like the occasional interface from a unique piece of hardware or a sensor to the PLC that may not already exist. I'm not a EE so i could be wrong, but thats my 2¢ fwiw.-sj

author: STCC
author_rank: Contributor
timestamp: May 07, 2012, 10:31:56 am
content: Whitneyrm that's pure gold!sonicj that's exactly my reasoning. Next interview is Wednesday and all will be revealed. I'll ask them about previous projects he's had to do and make everything clear, and just hope for the best.

author: Rerouter
author_rank: Super Contributor
timestamp: May 22, 2012, 08:51:35 am
content: Still, did they give you any indication as to what type interface, (arduinos arent that far from plc's) basic models tend to come with only digital in and digital out, and usually some bus connector, commonly HART, PROFIBUS, SCADA, and a few others of that genre,aftermarket interfaces are more commonly- A/D: Current 4-20mA commonly, but some 7-15mA stuff is still flaoting around though rare, if so allow for 3-21mA, but present some way of limiting it to 4-20 (some plc's go into alarm): Voltage 1-5V commonly, with 2-10 and 7-15V stuff floating around, if 1-5, allow for 0.75 to 5.125, and like current build in the option of a limit,: Milli-volt, depending on the type of thermocouple, it can be from about -100mV to +100mV, and these values i have not confirmed,- D/A: same as above, but there are some more fancy things like Variable speed drives that can be included under these,- A/A: is almost non existant, as a 250 ohm resistor can usually convert between the 2 common types, though thermocoule to current or voltage is somewhat common- D/D: this is where i suspect you may be playing with, as its not to uncommon for plants to want to control a few different types of units that may use different protocols off the one control system,also be aware, most plc gear is rated for 48V on any input and sometimes output, with alarm options in software for nearly anything,