# Schematics (understanding and drawing them) **URL:** \ **Category:** Uncategorized\ **Created:** [May 25, 2020, 3:08pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011 "2020-05-25T15:08:00Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [November 27, 2020, 9:53pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/41 "2020-11-27T21:53:29Z")
thank you guys ! (more carracters) ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [November 29, 2020, 6:36pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/42 "2020-11-29T18:36:17Z")
another noob question, the bypass cap on ic, it’s good for all ic or just with opamp ? ---
**Author:** ![eric](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@eric](https://lookmumnocomputer.discourse.group/u/eric)\ **Post date:** [November 29, 2020, 7:35pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/43 "2020-11-29T19:35:16Z")
For all ICs. They are small reservoirs of energy for when the IC needs it fast. Unless the datasheet says otherwise, use one 100nF between gnd and each power rail used by the IC. That means that cmos logic ICs for example just need one between +12V and gnd as they don’t use -12V (usually… I’m sure somebody comes up with cases where they are powered between +12V and -12V and not +12V and gnd…). They are a cent or two each and can’t hurt anyway… Power regulators need their own combination of decoupling caps… ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [November 29, 2020, 9:14pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/44 "2020-11-29T21:14:40Z")
> [@eric](#): > > They are small reservoirs of energy for when the IC needs it fast. and they short circuit HF signals on the power rail to GND which may have a positive effect on the stability of the IC’s workings. ---
**Author:** ![devicex](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/devicex/32/28_2.png) [@devicex](https://lookmumnocomputer.discourse.group/u/devicex)\ **Post date:** [November 30, 2020, 12:50am UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/45 "2020-11-30T00:50:49Z")
cool . thanks for posting these explanations , learning stuff today ! ---
**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\ **Post date:** [February 28, 2023, 1:27pm UTC](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011/46 "2023-02-28T13:27:29Z")
Regarding potentiometer pin numberings: In the KiCad footprints library, I believe all the horizontal board mount pots (ones with the shaft parallel to the PCB) have pin 1 counterclockwise and pin 3 clockwise: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/2/d/2dd26d6ac32700875aeb7279aa4a06d819230cba.png) ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/b/e/be18017375c2f60c95bbff833268c44c86ee933d.png) However, inexplicably, most of the vertical pots (shaft perpendicular to PCB) in the same library have pin 1 CW and pin 3 CCW. There are only a few exceptions including Potentiometer\_Alpha\_RD901F-40-00D\_Single\_Vertical: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/9/8/9845049135ebb47cad4677b08a42d727ec900bb3.png) ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/9/b/9b381bd77dbf71222681fe6b318ad8703229d805.png) ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/b/a/bac52e24ef18206474d8d99a50c5004e2d0f9b85.png) This is really bizarre especially since if you look at for instance the Bourns PTV09A datasheet it shows the pin numbering the other way around: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/3/0/303a45c23c20d943f049fcc04e343cd6ae0873dd.png) Maybe there’s some datasheet out there for some pot that has pin numbering with 1 clockwise but I don’t know of one. So I think this is _almost_ universally the accepted numbering, but it does _not_ agree with a significant number of KiCad footprints. To make my intentions clearer I use a custom pot symbol that has an arrow indicating clockwise rotation: ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/1/a/1aee06162ce406d07671f80007e930a316761b4e.png) and then for vertical pots I always use footprints similar to Potentiometer\_Alpha\_RD901F-40-00D\_Single\_Vertical. [Previous page](https://lookmumnocomputer.discourse.group/t/schematics-understanding-and-drawing-them/1011.md?page=2)