Suggestions for improving PCB board Design  - Page 1
Forum section: electronics / projects

author: GeorgeJr
author_rank: Newbie
timestamp: July 12, 2022, 04:42:31 am
content: I have made a total of one PCB Board design and while I'm handy at many things circuit design always has me scratching my head as it is like solving math problems. Many ways to do it and I don't know enough to say which way is a better design. I have a PCB Board today that I manually solder up and looking to have it assembled for the next years builds. I haven't had many issue, but the more robust the design the less I need to support issues which is worth a cost to me and the customer.Todays design:Buck Converter to take Automotive 12v (10-14.4v normal) down to 5v (12 V side has a Diode to prevent reverse hookup flowing current)I have a 470 uF capacitor (Helps if the servo is being stressed more then expected to buffer that draw from the LCD/Nano)Nano Clone Microcontroller5V output (To Servo)Signal output (for servo)Button inputsLCD displayReally simple design which I like, but also would like suggestions to improve.I've had really good luck with the buck converters. The highest Amp draw on the 12V side is under 0.7 amps. I see many other designs using linear voltage regulator Any reason to switch? Another idea I had was because the servo can take higher voltage than the microprocessor any advantage to using a linear regulator to drop 12V input to say 7.5 volts for the servo and another to drop from 7.5v to say 5v for the microcontroller?Today I'm using a Nano clone. With buying say 500 at a time would it make sense to just add the needed components onto the PCB board. I haven't priced this out yet but I see advantages both ways. One advantage I like with the Nano is being socket based I can swap them out quickly if any problem and the board stays the same. If the cost is low enough might be just as easy to swap out the full PCB board going forward.Voltage/current protection for the 5V microprocessor (Nano clone or chip feeding the 5V input) I've had a few fail and I can't pinpoint why I'm not using the regulator on the Nano today just feeding the 5v input. Replace the parts damaged and no other changes and works no problem. LCD, Nano have a burnt smell so guessing they are getting too high of voltage hooked up wrong or? The buck converter is never an issue after I swap parts and voltage is right on at 5v as it set it and glue it to stay at 5v.For the servo signal should I look to use OptiCoupler or a diode to avoid any chance of reverse voltage.To protect the microprocessor is a Zener diode 5.1v a good protection idea with resistor? Would this also be a good idea for the signal output instead of OptiCoupler or other method?Thanks for any suggestions as I look to redesign with as many surface mounted components for this new design. I will be happy not soldering boards and move onto other tasks. ;-) While it is fun it take way more time then the cost to have it done at this point. Thanks for your help.

author: RogerThat
author_rank: Regular Contributor
timestamp: July 13, 2022, 08:36:35 am
content: Some quick feedback and questions.I would skip the Nano and go directly to using just the MCU(MCU+LDO+caps) on the board. 1/5 the cost. If you are not using the MCU to keep time or external communication(UART/USB), no external crystal/clock is needed. The Atmega328 is also a bit hard to get these days...I would recommend looking at modern AVRs with UPID interface.For revers current I would recommend using a Pch MOSFET, less power loss. If you choose a small size it can also act like a fuse.Linear regulators are used for their low noise and simple/robust implementation, but they are inefficent and becomes hot when power goes up. If it is OK for your product to consume 20% more power and it can handle the heat, I would use a linear regulator. The waste heat from a linear regulator is: Amps x Voltage drop. Using a double drop (12->7.5 and then 7.5->5) can be used to spread the wasted heat over two components.There are monolithic switching supplies for PCB mount also, RECOM for example, costly but works out of the box. Zeners are not the best for circuit protection, look at ESD/TVS diodes. Every input/output that the final user of the product can poke their finger at should have ESD protection.If something smells burnt, it is running way too hot, find the issue!. Lifetime of electronic components goes down drastically when running hot, not to mention fire/smoke risk etc. Do you power the servo from the Nano 5V?RC servo with PWM control? No need for optocouplers if they run from the same ground and power. It can be useful to put series resistor(200R-10k...depending on use) from the MCU pins as a sort of protection, to limit current from/to the MCU. When using button inputs, don't forget to implement de-bounce circuit (74hc14 with RC filter on input). You write automotive so I guess you'r aiming for a car product? Search for components with AEQ-XXXX certification, they are built to higher standard and in some cases include flexible terminals to withstand vibrations better. Design wise, keep components away from the mounting holes on the PCB and mount them so that board flex affects them to a minimum. Aim to have everything on one board.

author: devinatkin
author_rank: Contributor
timestamp: July 13, 2022, 02:34:38 pm
content: So you mention you want to make 500 units. That sets a bit of context to your design. It makes using things like the Arduino clones less than desirable (Questionable quality control on them, plus they tend to cost more than putting the components directly when you get up in units). I'd recommend potentially switching to the RP2040 (Not sure about qualifications given the mention of Automotive certifications is a valid concern for being able to sell your products, that may very well limit you to different micros which I'm not familiar with) they are super easy to set up on a board, giving lots of IO and powerful peripherals to slot into existing designs pretty easily.Linear regulators are nice from a robustness standard as mentioned by the other commenter. But if you already have a functioning buck then I likely wouldn't switch. If I were you I'd go with a fixed voltage variety as opposed to an adjustable as it ends up saving components and beyond that means knocking it out of voltage is impossible (you glue it, but that just makes it hard not impossible).You mention a 470uF capacitor, if that's all. It'd be substantially better to split that into several smaller capacitors (a couple 10uF, 1uF, and 100uF) to get the best protection and ripple rejection. You don't want 1 capacitor cause if something goes wrong with it the board suddenly is busted for want of a good capacitor.Things like a zener clamp are not really necessary and they'll increase your power consumption as they'll start to conduct below that Zener voltage. Same with Optocouplers, they shouldn't be needed or useful in this case.An RC to debounce your switches would be good, although I'll admit I typically forget that and end up doing it in software.For assembly I recommend JLCPCBA which will help with doing a surface mount redesign.