Author Topic: spdt switch  (Read 4707 times)

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Offline fixit7Topic starter

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spdt switch
« on: May 21, 2019, 01:01:54 am »
I have  working circuit using my breadboard.

I used a full size spdt switch to turn the circuit on.

I ordered a switch to plug into the board to replace it, but it will not work.

Are there more than one type?

Andy
 

Offline MarkF

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Re: spdt switch
« Reply #1 on: May 21, 2019, 01:07:12 am »
Without any details of what the requirements are...
I have used these to switch signals and low current and voltage power lines.
   https://www.digikey.com/products/en?keywords=EG2459-ND


Edit -  These have gold contacts if that is a concern.
« Last Edit: May 21, 2019, 01:17:54 am by MarkF »
 

Offline Audioguru

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Re: spdt switch
« Reply #2 on: May 21, 2019, 01:13:36 am »
Most switches are made for high currents at the mains voltage so they have silver contacts. But for low voltage and low currents it fails when it becomes corroded.
Therefore I use switches with gold plated  contacts for low levels, these switches do not cost more.
 

Offline SL4P

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Re: spdt switch
« Reply #3 on: May 21, 2019, 01:57:14 am »
The pinout May be different.
Some have the wiper in the middle, some to one side.
Don't ask a question if you aren't willing to listen to the answer.
 

Offline Brumby

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Re: spdt switch
« Reply #4 on: May 21, 2019, 04:57:40 am »
Are there more than one type?
There are thousands of different types of switches, but for any given style, there can be a variety of configurations.

But, in all honesty, you haven't really given us enough information to provide a clear answer to your question.
 
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Offline fixit7Topic starter

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Re: spdt switch
« Reply #5 on: May 21, 2019, 11:25:20 am »
3-Pin SPDT Slide Switch
Number of pins: 3
Contact form: SPDT
Switch function: ON-ON
Contact rating: 0.3A @ 125VAC
Dimensions: 0.45"L x 0.16"W x 0.24"D
Lead spacing: 0.1" (2.54mm) - Breadboard friendly
Housing material: Plastic
Lead length: 0.24"
Actuator height: 0.12"
Actuator travel: 0.1"
PCB mount

https://www.dropbox.com/s/m3hq985tsujucsm/20190521_062111.jpg?dl=0
 

Offline Ruaeh123

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Re: spdt switch
« Reply #6 on: May 21, 2019, 12:51:56 pm »
The situation puts three main possibilities on the table:

1. The switch is faulty
2. You have connected your circuit between the two throws
3. Your circuit is non-functonal for whatever reason

The first thing I would do is, as SL4P said, check the pins with a multimeter in continuity mode to figure out the pinout and check if the swhitch is good or faulty.
There should be a combination of two pins that doesn't have continuity in any of the two positions of the switch(since these ate the two throws) and any other combination would have continuity in one of the two positions of the switch.
This will check the veracity of the first two possibilities, and if that's the case, the switch it's not the colprit

I hope I have been helpful :)
 
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Offline Brumby

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Re: spdt switch
« Reply #7 on: May 21, 2019, 04:05:29 pm »
That's terrific info!  (A bit more than needed - but too much is better than not enough!)

The classic operation of such a switch is there should be continuity between the centre connection and either of the two end connections, depending on which end the actuator is placed.

In the photo you provided (  :-+ ) with the switch actuator at the left (as shown) you should have continuity between the centre connection and the left connection.  With the switch actuator moved to the right, you should have continuity between the centre connection and the right connection.  If this is not the case, then it would seem you have a faulty switch.
 
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Offline exe

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Re: spdt switch
« Reply #8 on: May 21, 2019, 04:23:57 pm »
Just use multimeter to troubleshoot it.
 
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Online ebastler

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Re: spdt switch
« Reply #9 on: May 21, 2019, 04:29:40 pm »
I assume you are using a solder-less breadboard, where you just plug your components in from the top. Having looked at the picture of the switch which you provided via Dropbox -- do these contacts really fit into the breadboard sockets? They look like rather wide metal tabs, meant to solder wires to them.

How did you fit the switch to your breadboard? Are you sure it is making proper contact with the breadboard? Again, a multimeter will help you to diagnose this.
 
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Offline MarkF

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Re: spdt switch
« Reply #10 on: May 21, 2019, 04:38:35 pm »
Is the switch not working?
      OR
Are you looking for a replacement switch for a breadboard?
If so, what kind of breadboard?  Solderless or a prototype-board?
 
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Offline fixit7Topic starter

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Re: spdt switch
« Reply #11 on: May 21, 2019, 06:05:58 pm »
Is the switch not working?
      OR
Are you looking for a replacement switch for a breadboard?
If so, what kind of breadboard?  Solderless or a prototype-board?

With the larger switch, I soldered to the pins and ran the ends to my breadboard.

 

Offline fixit7Topic starter

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Re: spdt switch
« Reply #12 on: May 21, 2019, 06:17:45 pm »
The situation puts three main possibilities on the table:

1. The switch is faulty
2. You have connected your circuit between the two throws
3. Your circuit is non-functonal for whatever reason

The first thing I would do is, as SL4P said, check the pins with a multimeter in continuity mode to figure out the pinout and check if the swhitch is good or faulty.
There should be a combination of two pins that doesn't have continuity in any of the two positions of the switch(since these ate the two throws) and any other combination would have continuity in one of the two positions of the switch.
This will check the veracity of the first two possibilities, and if that's the case, the switch it's not the colprit

I hope I have been helpful :)

It was no. 1.

Switch was faulty.
 

Offline fixit7Topic starter

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Re: spdt switch
« Reply #13 on: May 21, 2019, 07:09:59 pm »
Not sure now.

The switch sometimes works, but most often does not.

Here is where it is used in.

When a laser is shined on the cadmium photocell, the alarm does not sound.

When the beam is interrupted, it sounds.



When I use the larger 3 amp switch, the circuit always works?
« Last Edit: May 22, 2019, 05:41:28 pm by fixit7 »
 

Offline Audioguru

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Re: spdt switch
« Reply #14 on: May 21, 2019, 07:28:42 pm »
The switch is faulty because its contacts are made for up to 300mA at 125VAC (peak voltages are 177V). But again, your schematic does not show the resistance value of R1 which probably has a current that is 1 millionth what the switch needs and your pin 2 voltage is 60 times too low for that high power switch. Use a switch with gold contacts made for low power.

Is the function of the switch to turn off the beeper when you want after it has been triggered?
 

Offline fixit7Topic starter

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Re: spdt switch
« Reply #15 on: May 21, 2019, 08:06:23 pm »
The switch is faulty because its contacts are made for up to 300mA at 125VAC (peak voltages are 177V). But again, your schematic does not show the resistance value of R1 which probably has a current that is 1 millionth what the switch needs and your pin 2 voltage is 60 times too low for that high power switch. Use a switch with gold contacts made for low power.

Is the function of the switch to turn off the beeper when you want after it has been triggered?

Resistor is 220 ohms.

Switch does turn off beeper when it is triggered.
 

Online Zero999

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Re: spdt switch
« Reply #16 on: May 21, 2019, 08:42:58 pm »
Why not put the switch in series with the entire circuit, rather than just the beeper?

Audioguru is mistaken about switches corroding, when the current and volt are too low. Using a switch at too lower voltage and current will not break it, but he does have a point that it might be unreliable. Switches with copper or solver contacts need to have a high enough voltage and current to ensure the oxide layer is broken, when the contacts make. This is known as the wetting current. If the current is too low, then the switch might not operate reliably. The solution is to use a switch with gold plated contacts, which doesn't suffer from this issue because gold doesn't oxidise.
 

Offline Brumby

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Re: spdt switch
« Reply #17 on: May 22, 2019, 01:51:59 am »
It's a slide switch.  The mechanical action of contacts sliding should be more than enough to break any oxide layer unless it is excessive.  Long term storage in less than ideal conditions could cause that.  Then there is the possibility of other contaminants getting onto the contact surfaces.

Both of the above conditions can sometimes be rectified by operating the switch several times, possibly in conjunction with a switch/contact cleaner.

If this doesn't fix things, then the switch would seem to have a more severe mechanical fault.



The other thing you can do (if you haven't already) is to try the two combinations available (centre and left -or- centre and right) and see if one is reliable.
 

Offline fixit7Topic starter

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Re: spdt switch
« Reply #18 on: May 22, 2019, 02:15:02 am »
Why not put the switch in series with the entire circuit, rather than just the beeper?

Audioguru is mistaken about switches corroding, when the current and volt are too low. Using a switch at too lower voltage and current will not break it, but he does have a point that it might be unreliable. Switches with copper or solver contacts need to have a high enough voltage and current to ensure the oxide layer is broken, when the contacts make. This is known as the wetting current. If the current is too low, then the switch might not operate reliably. The solution is to use a switch with gold plated contacts, which doesn't suffer from this issue because gold doesn't oxidise.

I am not sure how to put the switch in series with the circuit.

The switches connects with pins 2 and 3 of the 555 chip.
 

Offline Brumby

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Re: spdt switch
« Reply #19 on: May 22, 2019, 02:33:14 am »
The suggestion means joining pins 2 and 3 of the 555 and putting the switch in the power to the circuit so that the whole circuit is turned on or off.
 
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Offline fixit7Topic starter

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Re: spdt switch
« Reply #20 on: May 22, 2019, 11:32:36 am »
I should have shown this earlier.

https://www.dropbox.com/s/0dyg6wogy341lhd/KEEP_circuit.jpg?dl=0

I have a 3rd wire going from switch to the negative of the buzzer.
 

Offline Richard Crowley

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Re: spdt switch
« Reply #21 on: May 22, 2019, 11:44:18 am »
Your photo shows a DOUBLE pole, double throw (DPDT) switch.  But your circuit is using only one "pole".  It is common to see double pole switches connected with the poles in parallel. That provides a rather more reliable action for small-signal applications like yours. I would strap the sections in parallel if you don't need double-pole operation.  Old-school open slide switch designs like that are not necessarily reliable for very low power applications.
 

Online ebastler

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Re: spdt switch
« Reply #22 on: May 22, 2019, 12:16:53 pm »
Your photo shows a DOUBLE pole, double throw (DPDT) switch.

I see a SPDT switch, and a shadow.
 

Offline fixit7Topic starter

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Re: spdt switch
« Reply #23 on: May 22, 2019, 03:12:03 pm »
Your photo shows a DOUBLE pole, double throw (DPDT) switch.  But your circuit is using only one "pole".  It is common to see double pole switches connected with the poles in parallel. That provides a rather more reliable action for small-signal applications like yours. I would strap the sections in parallel if you don't need double-pole operation.  Old-school open slide switch designs like that are not necessarily reliable for very low power applications.

I must need a double pole switch because when I substituted a spdt switch, the circuit stopped working correctly.

 

Offline Richard Crowley

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Re: spdt switch
« Reply #24 on: May 22, 2019, 03:13:12 pm »
I must need a double pole switch because when I substituted a spdt switch, the circuit stopped working correctly.
That makes no sense at all.  Your circuit clearly shows a SINGLE pole, double throw switch.
 


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