Please say everything you can to critique my design - Page 1
Forum section: electronics / projects

author: smashedProton
author_rank: Frequent Contributor
timestamp: January 18, 2013, 12:44:06 am
content: Hello all, I have been working on my first official project now. I am learning the ins and outs of schematic and pcb design. This is a room controller for my room where it uses a switch on my door, pir sensor, and an RTC. The lights in my room are controlled by the bjt near the pin header. I made this because i would rather be woken up by lights rather than sound. Bootstrapping my wake up process. Please tell me what I am doing wrong before i manufacture it. Thanks

author: svofski
author_rank: Regular Contributor
timestamp: January 18, 2013, 01:01:37 am
content: I can see overlapping traces on the top layer. Run DRC check.

author: smashedProton
author_rank: Frequent Contributor
timestamp: January 18, 2013, 02:39:48 am
content: Sorry, I did not explain that. They are jumper wires. It is a single layer design

author: kaindub
author_rank: Regular Contributor
timestamp: January 18, 2013, 03:59:43 am
content: Good design takes practiceI can look at this board and tell, but I don't know why, that I could make it a lot better. But that's because I have designed hundreds of boardsThe first thing I can see is that you should place IC1 and your controller parallel to the header. You'll then end up with parallel tracks between the header and the chips. the tracks will be shorther and as a bonus your board will be smaller.I also think you have too many jumpers. On a board of this size I would have may 5 or 6 jumpers max.Why don't you sleep on it and try again.Save the current layout. Then save it again as a new file. Then start rearranging parts. I always save interim versions (in case I cause create a real disaster I have something to go back to)Make it beautiful. I find that if it looks like a work of art, then it probably will be a good design (Work of art - chips running in same direction; compoenents running in same direction; tracks short and parallel to each other; polarised caps all in the same directio; diodes in the same direction)

author: Harvs
author_rank: Super Contributor
timestamp: January 18, 2013, 08:26:05 am
content: QuoteJust reading that makes my skin crawl! I can't think of anything worse than having the lights come on a 530 - 6 in the morning, you must be a real sucker for punishment!If you're going to use jumpers (which you almost certainly will with a single sided board), I really like the old skool way of tinned, non-insulated wire. They just look neat, easy to install, and look like they aren't a bodge job. To that end, crossing jumpers are a no-no, and jumper should be spaced at reasonable intervals (like you would place a 1/4W resistor.)So is the choice for a single sided board driven by home manufacture? If not, it's very cheap to get double sided boards done these days up to 10x10cm and dispense with the jumpers all together.

author: c4757p
author_rank: Super Contributor
timestamp: January 18, 2013, 02:39:11 pm
content: Above C5, you have a ground jumper going across a power trace. I don't think grounding istoocritical in this circuit, but given the choice I'd keep ground uniform and unbroken and put the jumper on the power trace instead.Also,decoupling! Again, probably not critical, but you've got both analog and digital in that circuit sharing a power rail. I'd throw in a few capacitors on both the analog and digital ICs. The 555s are especially bad, they take pretty big current spikes and should probably have large capacitors.

author: svofski
author_rank: Regular Contributor
timestamp: January 18, 2013, 03:59:30 pm
content: I would listen to kaindub's advice and try to rearrange all parts in a more elegant manner. Probably there is going to be less jumper wire, too.

author: smashedProton
author_rank: Frequent Contributor
timestamp: January 18, 2013, 06:40:06 pm
content: Quote from: Harvs on January 18, 2013, 08:26:05 amHa! My problem is that I hate waking up to alarms that make me run across the room to turn off. And if i have the alarm next to my bed, i turn it off anyway. This just automates the first thing i do every day anyway. I'm a teenager. what the hell

author: SeanB
author_rank: Super Contributor
timestamp: January 18, 2013, 06:46:38 pm
content: I did that with an old clock radio and it turns on the bedside lamp, which is older than anybody here on this forum ( I do not think anybody here was born before 1939) and has been working this way for years, though I have had one SSR fail after 10 years, but it was a used one anyway from a 1970's Xerox copier I got parts from, from the technicians who used to work for AM International.

author: LEECH666
author_rank: Frequent Contributor
timestamp: January 21, 2013, 12:37:47 pm
content: I am not a professional but there are a lot of odd things in your design.- Weird angles of traces all over the place, try either to stick to 90° only or 45° angles. (45° is more common, it just looks neat.)- Why is there a pad under pin 8 of IC5?- Track too close to the jumper wire pad (the track that's passing through pin 6/7 of IC5)- Jumper wire connected to pad of T1 (?)The list goes on and on ...You should probably read this Tutorial written by Dave and try again.http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdfCheers,Florian

author: ptricks
author_rank: Frequent Contributor
timestamp: January 21, 2013, 01:03:15 pm
content: Add decoupling caps to all the chips.Don't leave any processor pins floating, if not used tie them to ground through a resistor. Stray voltages on the board and from the unused pins can cause problems.When drawing out the schematic avoid drawing lines that cross each other, don't rely on the little dot to show when something is connected or not, it makes for difficult reading.Mark the pins on the schematic as either input or output or bidirectional using arrows followed by the word of the location the part connects to , using the words input and output on the schematic can get confusing as to whether you mean the parts connecting to an input or is it the input coming from a part.

author: dr_p
author_rank: Frequent Contributor
timestamp: January 21, 2013, 03:01:54 pm
content: Quote from: smashedProton on January 18, 2013, 06:40:06 pmI'm not a teenager and still have lots of trouble waking up.My girlfriend and I start hearing alarms going off from 6:00. That's 11 alarms, 15min spaced out, all snoozed 10x3min. On top of that,music starts playing through from the PC, on 50% volume on 30W RMS speakers. We touch the ground at 7:30, and trust me, it's an unbearable wrack. There's a backup desk clock set at 8:00 just in case we miss them;)On-topic: have you considered mounting holes?

author: smashedProton
author_rank: Frequent Contributor
timestamp: January 23, 2013, 04:12:36 am
content: On-topic: have you considered mounting holes?I have considered. I made the educated decision to tape it to the wall.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 23, 2013, 04:27:50 am
content: Since you have a microcontroller, the 555s are not necessary. Also take out D2 as it is not necessary.

author: lgbeno
author_rank: Frequent Contributor
timestamp: January 23, 2013, 12:43:32 pm
content: Do you plan to etch this at home or send it out to be made? If you are sending out to be made, I would suggest not over constraining yourself and doing a dual layer board. I didn't measure the design but if it is 5cm x 5cm or less, that would only cost you $13 with shipping from iTead or Seeed. Well worth the money in my opinion. Also did you consider an enclosure since this is going to be an installation in your room? That might drive requirements for mounting holes or a certain shape/size.

author: Kremmen
author_rank: Super Contributor
timestamp: January 23, 2013, 04:59:00 pm
content: Since this is a Mega168 it supports debugWire protocol. But that requires you to connect the reset line of the ISP header to the chip reset pin . And then you need to make sure that R17 is at least 10k or more. I always use a 22k pull-up and that has never given any trouble.