Author Topic: Switch pain  (Read 1912 times)

0 Members and 1 Guest are viewing this topic.

Offline PerranOakTopic starter

  • Frequent Contributor
  • **
  • Posts: 552
  • Country: gb
Switch pain
« on: June 10, 2019, 04:46:45 pm »
Switches and buttons give me more pain than any other component!

I have a microcontroller pin that has a pull-up resistor. All I need is a simple slide switch (PCB mounted, through-hole, about 8mm x 4mm ish) for the user to take this pin low while other things are selected then to return it to the pull-up situation.

So is this an SPDT, SPST, this, that or what!?!? Argh!  |O

Any help, gratefully received.
« Last Edit: June 10, 2019, 04:49:00 pm by PerranOak »
You can release yourself but the only way to go is down!
RJD
 

Offline Buriedcode

  • Super Contributor
  • ***
  • Posts: 1718
  • Country: gb
Re: Switch pain
« Reply #1 on: June 10, 2019, 04:56:26 pm »
The P is the number of poles - how many actual switches are inside the switch either a number of S for single, D for dual, and T is toggle - how many ways each individual switch can be switched.  Eg DP4T has two separate switch, each common can connect to 4 nodes.

If you just need to pull a pin low/high then you only need one toggle, and one pole - SPST.  But you can of course use SPDT as you just need the NC (normally closed) unconnected.  And you can use DPDT and just leave one whole switch unconnected.

In my experience, you narrow down the search first by type (slide, toggle, rocker etc..) then by termination (PCB, solder lug, tab, screw terminal).
 

Offline MarkF

  • Super Contributor
  • ***
  • Posts: 2762
  • Country: us
Re: Switch pain
« Reply #2 on: June 10, 2019, 05:07:56 pm »
Maybe this will help:

   
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Switch pain
« Reply #3 on: June 10, 2019, 05:16:23 pm »
I have a microcontroller pin that has a pull-up resistor. All I need is a simple slide switch (PCB mounted, through-hole, about 8mm x 4mm ish) for the user to take this pin low while other things are selected then to return it to the pull-up situation.

Not being American I always found the pole-throw nomenclature kind of silly.

If you are using the switch with a microcontroller you want to be very careful with debouncing.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 10172
  • Country: gb
Re: Switch pain
« Reply #4 on: June 10, 2019, 05:56:38 pm »
The P is the number of poles - how many actual switches are inside the switch either a number of S for single, D for dual, and T is toggle - how many ways each individual switch can be switched.  Eg DP4T has two separate switch, each common can connect to 4 nodes.

The T actually stands for throw, not toggle, as in 'throw the switch'.
Best Regards, Chris
 

Offline KL27x

  • Super Contributor
  • ***
  • Posts: 4108
  • Country: us
Re: Switch pain
« Reply #5 on: June 10, 2019, 08:02:18 pm »
Quote
Not being American I always found the pole-throw nomenclature kind of silly.
In my personal experience, being American doesn't help. I have never been able to remember pole from throw. It seems backwards, if anything. Do you want to throw 1 switch at a time or 2 or 3? How many poles do you want to connect with each throw? Totally backwards, if I try to make it sensible.

Quote
T actually stands for throw, not toggle
Well, I might actually remember it like that. I like toggle.

Humm. I like P for pins (like ribbon cables; 10P is 10 parallel "connections"), T for toggles.
« Last Edit: June 10, 2019, 08:11:23 pm by KL27x »
 

Offline ajb

  • Super Contributor
  • ***
  • Posts: 2785
  • Country: us
Re: Switch pain
« Reply #6 on: June 10, 2019, 08:27:18 pm »
I have a microcontroller pin that has a pull-up resistor. All I need is a simple slide switch (PCB mounted, through-hole, about 8mm x 4mm ish) for the user to take this pin low while other things are selected then to return it to the pull-up situation.

Not being American I always found the pole-throw nomenclature kind of silly.

As opposed to what, the Form A/B/C/D naming? 
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Switch pain
« Reply #7 on: June 10, 2019, 08:58:50 pm »
In Spanish:

SPST is just a breaker or interruptor

SPDT is a "conmutator" or switch

And the "poles" are "circuits".

A "3 circuit breaker" breaks 3 circuits, like for a three phase motor.

A 3 circuit switch would be a 3 pole double throw

If you have more than two "throws" then you talk about "positions".

A "one circuit 10 position" switch allows one input to be connected to any one of 10 outputs.

A "2 circuit, 10 position" is the same but duplicated, with two circuits.

In other words, "circuits" are the number of inputs and "positions" are the number of outputs for each input.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline ArthurDent

  • Super Contributor
  • ***
  • Posts: 1193
  • Country: us
Re: Switch pain
« Reply #8 on: June 10, 2019, 10:14:42 pm »
It helps if you know the evolution of switches. From around 1900 on, the ‘knife’ switch was very common and the name came from the moveable arm of the switch resembling a knife blade. To connect this contact to complete the circuit you had to move or ‘throw’ the blade so it slid between the two halves of the fixed contact. Anyone who has watched an old Frankenstein horror movie or a gangster movie from the 1930s where the villain gets the electric chair has seen them ‘throw the switch’. The photo below is an example of a knife switch. Some of the terms from these days carried over so that is why you when you activate a modern small switch it is still referred to as ‘throwing the switch’ or with switches getting smaller and smaller, ‘flipping’ the switch.
 
Each separate circuit is referred to as a ‘pole’ and SPST or 1P1T are used interchangeably but when you start talking about center off double throw switches it is easier to refer to them as ON-OFF-ON. As mentioned above, once you get to multi contact rotary switches they have a certain number of of decks, and poles, and a number of positions, not throws.

Conventional terms can be confusing as when you record a video and use terms like ‘film’ or ‘tape’, when neither is involved, or for that matter, there’s no record!
 
The following users thanked this post: soldar

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Switch pain
« Reply #9 on: June 10, 2019, 10:34:50 pm »
or for that matter, there’s no record!

To "record" means to register some information on any permanent media so it can be reproduced and consulted at a later time. Records of laws or other information were kept on clay tablets, papyrus, parchment, paper and now electronic media.

Etymology: from Old French record ‘remembrance’, from recorder ‘bring to remembrance’, from Latin recordari ‘remember’, based on cor, cord- ‘heart’. The noun was earliest used in law to denote the fact of being written down as evidence.

So yes, "record" is correct. :)
« Last Edit: June 10, 2019, 11:30:51 pm by soldar »
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline ArthurDent

  • Super Contributor
  • ***
  • Posts: 1193
  • Country: us
Re: Switch pain
« Reply #10 on: June 10, 2019, 11:34:53 pm »
Quote
"To "record" means to register some information on any permanent media so it can be reproduced and consulted at a later time. Records of laws or other information were kept on clay tablets, papyrus, parchment, paper and now electronic media.

So yes, "record" is correct. :) "

Sorry that my humor doesn't translate well. The verb 'record' is correct but my reference was to the noun, 'record', a physical disk with music or whatever recorded on the record.   8)
 

Offline PerranOakTopic starter

  • Frequent Contributor
  • **
  • Posts: 552
  • Country: gb
Re: Switch pain
« Reply #11 on: June 11, 2019, 03:34:44 pm »
Thank you all very much.

So, I need an SPST.

I've got the de-bouncing in software: I love doing that kind of programming.

Out of interest, in the diagram I get why SPST has "on-off" but why does the SPDT have "on-off-on" and "on-on"?
« Last Edit: June 11, 2019, 03:36:35 pm by PerranOak »
You can release yourself but the only way to go is down!
RJD
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Re: Switch pain
« Reply #12 on: June 11, 2019, 04:00:30 pm »
Out of interest, in the diagram I get why SPST has "on-off" but why does the SPDT have "on-off-on" and "on-on"?
Some do, some don't. Some have two positions, On-On, and other have three with a neutral stop in the center, On-Off-On.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf