Dummy Check/Will this work? - Page 1
Forum section: electronics / projects

author: GhostDog
author_rank: Newbie
timestamp: July 31, 2021, 02:17:19 am
content: Hi All,First post on the forum, although I've been doing electronics for about 9 years at this point.I've just finished a project using the ATTINY85 micro-controller, and (hopefully) transported it to a PCB design.This is my first ever time designing a PCB, and will also be my first time soldering SMD components (although I do have a rework gun, as well as about 20 different tips for my iron).I wanted to check that I've gotten my PCB design correct (and if there's any best practices i should be following), and that it will also work as it has on the breadboard I've been using.And my breadboard layout: (excuse the terrible Fritzing drawing, couldn't get KiCad to do a breadboard drawing for some reason)

author: sleemanj
author_rank: Super Contributor
timestamp: July 31, 2021, 02:45:36 am
content: C1206 is incorrectYour input ground is not connectedI assume there is a good reason you are using different sized resistorsAesthetically the 4-way intersection under the switch is ugly, and aesthetically the right angle connection just below C1206 could be pushed into a nice 45 degree.Equivalence to the breadboard or functional correctness not examined other than above.

author: GhostDog
author_rank: Newbie
timestamp: July 31, 2021, 03:04:58 am
content: Knew something felt a bit offI can see a few more mistakes now too, Any tips for fixing the ugly-ness of the intersection beneath the switch?(P.S. the only reason I'm using different sized resistors is they act as convenient jumpers in some spots, and I'd need them anyway)I've also added a filtering cap between VIN and GND on the regulator as per the datasheet.

author: sleemanj
author_rank: Super Contributor
timestamp: July 31, 2021, 05:11:48 am
content: I would probably have done like this...rather than a single 4 way intersection 2x 3way ones. Of course, its purely aesthetic.If you are fabbing the PCB yourself (hence using resistors to jump rather than double sided) then you migh as well make the traces fatter too, make it much easier to etch reliably.

author: Bassman59
author_rank: Super Contributor
timestamp: July 31, 2021, 05:33:18 am
content: Oh, where to start.The tab of the regulator must connect to its pin 2, and you really want to connect it to a large copper area so it can act as a heat sink. I know the circuit probably doesn't draw much power at all, but still if your input voltage is at the 6V max there's a decent voltage drop across the regulator.Whatisyour input voltage, anyway? If you're clever and you know the current draw you can dial it down to 3.6 V. The regulator will still work and you don't drop much in it.The regulator output on Pin 3 goes nowhere.Corollary to that, you need to put the 1uF cap between regulator output Pin 3 and ground, which is regulator Pin 2. Regulator Pin 3 needs to go to the micro's VCC pin 8 and that other stuff.The Fritzing drawing is terrible. Why not screen-shot the Kicad schematic? That would help us a bunch.

author: sleemanj
author_rank: Super Contributor
timestamp: July 31, 2021, 06:15:22 am
content: Quote from: Bassman59 on July 31, 2021, 05:33:18 amIt would be a strange regulator if pin 2 and the tab were not connected internally, there should be no need electrically to connect them externally, you can draw current from either.For heatsinking, yeah you want some more copper on the tab if it's going to be passing any significant current.

author: magic
author_rank: Super Contributor
timestamp: July 31, 2021, 07:23:33 am
content: Quote from: GhostDog on July 31, 2021, 02:17:19 amIt may have a schematic drawing function, though

author: TomS_
author_rank: Frequent Contributor
timestamp: July 31, 2021, 07:50:28 am
content: My 2¢The center pin on each side of the switch is common, so will be connected internally, and thus you don't have to connect the two externally. So pick one side and connect to it, and that will help alleviate the aesthetic blemish people are moaning about.220 ohm pull down resistors are overkill. Increase them to 10k and save quite a few mA depending on the position of the switch.3.3V / 220ohm = 15mA3.3V / 10Kohm = 330uA

author: GhostDog
author_rank: Newbie
timestamp: August 01, 2021, 06:13:39 am
content: I've made a bunch of "improvements" (from what i can judge, so probably mistakes at this point lmao), and have tried to make sure everything atleast work...I've also used a different BCD switch as it is easier to get.Thanks a heap again for everyone's help.