
How to Read a Schematic - iuguy
https://rawhex.com/blogs/news/how-to-read-a-schematic
======
Animats
That's a breakout board - mostly connectors, little functionality. Not too
interesting to study. A simple blinky board with a 555 timer would be a better
place to start.

Here's one of my schematics[1] with a detailed explanation of how it works [2]
This is a small board which is used to power old Teletype machines. It's a
mixed analog/digital board, with a custom switching power supply onboard to
provide the high output voltage needed using only power from the USB port.

This gives some insight into why modern power supplies have so many parts.
They work by creating big spikes, and they're always a few microseconds from a
short circuit. So they need bypass capacitors and ferrite beads in the right
places, and protection circuitry in case something fails. (MOSFETs tend to
fail into the ON state.)

If you really want to learn this stuff, get "The Art of Electronics", by
Horowitz and Hill.

[1] [https://raw.githubusercontent.com/John-
Nagle/ttyloopdriver/m...](https://raw.githubusercontent.com/John-
Nagle/ttyloopdriver/master/board/ttydriver01.png)

[2] [https://github.com/John-
Nagle/ttyloopdriver/blob/master/READ...](https://github.com/John-
Nagle/ttyloopdriver/blob/master/README.md)

~~~
sleavey
+1 for using KiCad to draw the schematic - it's important to use open source
software when you're developing open source hardware. The licences for Altium,
Eagle and co can cost many hundreds or thousands of dollars/euros/pounds a
year, which bars entry to a lot of hobbyists. Improving what is already a
fantastic piece of software (KiCad) is a big priority in my view. It's good
that places like CERN are getting behind it.

~~~
Nanite
Eagle has a free licence version, If you're ok with 2 layer pcb's and fairly
small boards, which would suit quite a lot of hobbyists. KiCad was in need of
some UX love back when I looked at it 2 years ago, the feature set is
definitely impressive though, maybe time to revisit it in the near future.

~~~
sleavey
The software is still in a strange transition between the old layout engine
and the new OpenGL one developed by CERN. I believe the old interface is being
killed, but not immediately - you can switch between them as you use Pcbnew
(KiCad's board editor). I initially found the old interface to be more
intuitive, coming from Eagle. I used the new one for my most recent boards
(primarily due to its support for differential pair routing), and once I
learned the interface I now much prefer it.

There are still a few quirks, like, for instance, if I want to delete a whole
track, I find it quickest to switch to the old interface and press "Del", then
switch back. The new interface only deletes segments of tracks with that key.
Saying that, despite the rough edges it's pretty solid and functions
effectively in the professional and research environments I've worked in. It's
only going to get better, too, as the community grows and the new interface
fully replaces the old one.

~~~
Kliment
I use Kicad these days but am an Eagle refugee too. The only thing I use the
old interface for is the spread and place all components function, which I
can't find in the new one. For deleting tracks I use i and u to select either
the local segment or the whole track, and then press delete. One thing I'd
really like to have is have the shove router do its thing when moving
components that already have traces connected.

------
netvarun
One trick I learned at university while analyzing a circuit is to identify the
various 'design patterns' in it - just like software engineering, circuit
design also features a lot of recurring common patterns.

Here is a fantastic post on it:
[http://www.arachnidlabs.com/blog/2013/10/17/electronics-
patt...](http://www.arachnidlabs.com/blog/2013/10/17/electronics-patterns/)

~~~
cjsuk
Exactly this. The first step for me is usually to redraw out the messed up
crap the last person drafted as things that look like the design patterns.

Even Tektronix and HP can produce some dire schematics so when you've got your
head in some old kit I'd probably spend more time deciphering the service
manual schematics than actually fixing it (something I do as a leisure
activity)

------
metaphor
A few pro-tips on _drawing_ schematics:

1\. ASME Y14.100 and its references, in particular, Y14.1, Y14.2, and Y14.44.

2\. IEEE Std 315 for symbols and reference designators.

3\. Zen feng shui a la Tufte.

4\. For multi-sheet schematics, provide a list of every reference designator
and applicable sheet(s). Use sheet/zone references for all labels that span
multiple sheets.

5\. In general, functional left-to-right flow tends to be optimal for
interpretation. Keep the application intent in mind.

6\. Sideways text is _never_ acceptable.

7\. Q0O5S2Z1IX...if these characters aren't distinct, your typeface is busted.

8\. Minimize net crossings. If you feel cross-eyed looking at any sheet, your
schematics are likely busted.

9\. Assume black/white printing. If you need colors to disambiguate, your
schematics are certainly busted.

10\. Electrical schematics convey _eletrical intent_ , mechanical drawings
convey _mechanical intent_. Sometimes it's useful to convey elements of the
latter in the former.

