Where is pin #1 for NE555P - Page 1
Forum section: electronics / beginners

author: fixit7
author_rank: Regular Contributor
timestamp: May 06, 2019, 08:10:14 pm
content: I looked at the data sheet for this ne 555p chip. I can not figure out where the pin locations are.?The picture shows a half circle on the chip which tells me nothing.https://www.dropbox.com/s/fitler9s3jt0i64/NE555P.jpg?dl=0As in where is pin #1 in my picture?Thanks,Andy

author: Howardlong
author_rank: Super Contributor
timestamp: May 06, 2019, 08:22:38 pm
content: The circular indent in the package points you towards pin 1, in the traditional orientation package diagram of DIP, SOIC and SSOP packages, pin 1 is almost always shown top left.Thus, the two traditional standards for DIP are a marker at the top or a marker at the top left. Irrespective, if the chip is oriented with its marker to the top (or top left), pin 1 is ALWAYS at the top left.To be clear in your picture’s orientation, which is at 90 degrees to a standard pinout diagram, the top row of pins is 8 7 6 5Bottom row is 1 2 3 4.If you turn your picture clockwise 90 degrees, the marker is at the top left, the same a standard DIP pinout diagram.Edit: this is an interesting noob question, because it’s one of those things “everyone knows”. Except they don’t.Edit 2: added some more details, I can’t help feeling my pudding is over egged now.(What’s more frustrating is that for some packages, manufacturers sometimes show you the view from the bottom, not the top. I have never seen this for DIP though, markings are always shown from the top.)

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2019, 08:41:19 pm
content: I remember having this specific problem when I was a kid. Even the otherwise excellent Forrest Mims book I had did not show this detail as I recall and the internet was not a thing then so it was not easy to find the answer. It's something that is very simple once you know it, but without knowing that pins count up counter-clockwise around the IC from the lower left corner it is not obvious.And I think the above answer has an error, looking down on the top of the IC pin one is the *bottom* left, not the top.

author: Howardlong
author_rank: Super Contributor
timestamp: May 06, 2019, 09:11:22 pm
content: Quote from: james_s on May 06, 2019, 08:41:19 pmI may be misunderstanding, are you referring to this?“in the traditional orientation package diagram of DIP, SOIC and SSOP packages, pin 1 is always shown top left.”Or this?“If you turn your picture clockwise 90 degrees, the marker is at the top left, the same a standard DIP pinout diagram.”Or something else?

author: 6PTsocket
author_rank: Regular Contributor
timestamp: May 06, 2019, 09:28:49 pm
content: With the notch up, looking at the top of the chip, pin 1 is to the left of the notch and the numbers go CCW around the chip. If it is an 8 pin chip, pin 8 is on the other side of the notch.Sent from my SM-G900V using Tapatalk

author: Howardlong
author_rank: Super Contributor
timestamp: May 06, 2019, 09:30:13 pm
content: Here you go. You can have either marker. Sometimes it’s not a physical indent, it can be a printed marking. Very occasionally there’s no explicit orientation marking at all, and you use the printed part details to determine the orientation. In that case the start of the text is the top marker.This seems to cover all basis far better that I have.https://www.evilmadscientist.com/2010/basics-finding-pin-1/

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 06, 2019, 09:50:01 pm
content: Quote from: fixit7 on May 06, 2019, 08:10:14 pmHere:

author: mariush
author_rank: Super Contributor
timestamp: May 06, 2019, 09:55:15 pm
content: Or you could just be smart about it and look into the datasheet.You know it's NE555P and it has the texas instruments logo so you googleNE555P datasheet filetype:pdfand you get the datasheet.Link :http://www.ti.com/lit/ds/symlink/ne555.pdfThird page tells you the pinout :

author: helius
author_rank: Super Contributor
timestamp: May 06, 2019, 10:08:25 pm
content: I agree that it seems to be one of the things "everybody knows". In the otherwise very nice pinout diagram from the datasheet, neither the correct orientation of the text nor the actual dot are depicted. It simply assumes that you have already worked out for yourself how to find pin 1.

author: fixit7
author_rank: Regular Contributor
timestamp: May 06, 2019, 10:43:56 pm
content: Thanks for all the replies.I think I realize that I will need at least 2 more things.This so I don't burn out my chiphttps://www.amazon.com/gp/product/B00OK9BKAG/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1andhttps://www.ebay.com/itm/2x-5-x-10-cm-DIY-PCB-Prototype-Circuit-Solder-BREADBOARD-Discrete-and-DIP/141677397222?hash=item20fca184e6:g:lUAAAOSwPcVVvnaf#shpCntId

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2019, 11:41:28 pm
content: Quote from: Howardlong on May 06, 2019, 09:11:22 pmApparently my reading comprehension suffers a bit on a Monday morning.I was thinking in terms of the IC being oriented so that the printing on it is right side up, so the dot is on the left and pin 1 is the bottom-left pin. If you rotate the IC "sideways" so the notch is at the top then pin 1 is going to be the top-left.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 07, 2019, 12:20:37 am
content: If Pin 1 is at top left, why is the printing on the IC always sideways?Wouldn't it make more sense to have the printing horizontal as is normal, and the Pin 1 be the bottom left?Now, what is really confusing is when the schematic has the pins all mixed up for routing purposes and they are labeled by their functions rather than their numbers. I think that must be done as a cruel joke by designers played on beginners.

author: Nerull
author_rank: Frequent Contributor
timestamp: May 07, 2019, 01:46:33 am
content: The dot should only be trusted if there is no notch and it is specifically called out in the datasheets. You will encounter ships that have that injection moldering dot on the complete opposite end of the chip from the pin 1 notch.

author: james_s
author_rank: Super Contributor
timestamp: May 07, 2019, 03:22:58 am
content: Quote from: alsetalokin4017 on May 07, 2019, 12:20:37 amThat's done for a very good reason, pins are grouped by function to enable clear, logically drawn schematics that are easy to read. I find it very annoying and cumbersome when schematics are drawn with the pins in actual physical locations, maybe it's ok for very early beginners but it would drive engineers nuts and result in ugly hard to follow schematics.