question about G2R2 relay

On 24/09/14 01:00, AJ Weiner wrote:

I am trying to design a small board (my first) that incorporates three

G2R2 relays.  I found the component in the "add" section but it appears

that the schematic and the board drawings are different, specifically

the N.O. and N.C. contacts.  The actual part has the N.C. contact as the

one closest to the coil (as shown in the board image).  I am

miss-reading the two images or is it as simple as rotating the

N.O-Com-N.C. connection in the schematic?  I attached a screenshot of

the G2R2 part images.  Thanks.

 

There is no reason to think anything is wrong based on this screenshot.

Never assume that the schematic symbol has any geometric similarity to

the physical part. THIS IS NOT WHAT SCHEMATICS ARE FOR! How many

transistors do you know that physically look like their schematic

symbol? How many NAND gates in D-shaped packages?

Schematics represent function, not layout. That is precisely why the

contact part(s) of a relay are separate from the coil - you may want to

represent the function in different parts of the sheet (or even on

different sheets).

If it bugs you, you can rotate the contact parts. You can even make a

net connection between the NC pins and confirm that the board has the

airwire between the pins you expect.

HTH Rob

On 24/09/14 01:00, AJ Weiner wrote:

I am trying to design a small board (my first) that incorporates three

G2R2 relays.  I found the component in the "add" section but it appears

that the schematic and the board drawings are different, specifically

the N.O. and N.C. contacts.  The actual part has the N.C. contact as the

one closest to the coil (as shown in the board image).  I am

miss-reading the two images or is it as simple as rotating the

N.O-Com-N.C. connection in the schematic?  I attached a screenshot of

the G2R2 part images.  Thanks.

 

There is no reason to think anything is wrong based on this screenshot.

Never assume that the schematic symbol has any geometric similarity to

the physical part. THIS IS NOT WHAT SCHEMATICS ARE FOR! How many

transistors do you know that physically look like their schematic

symbol? How many NAND gates in D-shaped packages?

Schematics represent function, not layout. That is precisely why the

contact part(s) of a relay are separate from the coil - you may want to

represent the function in different parts of the sheet (or even on

different sheets).

If it bugs you, you can rotate the contact parts. You can even make a

net connection between the NC pins and confirm that the board has the

airwire between the pins you expect.

HTH Rob

Thank you for the response.  I am very new to electrical designs and schematics and you bring up some good points. 

It did really bug me and I spent a long time trying to get the two to look the same.  Also, is this the same reason why sometimes I would connect a net to the contact on the "left" of the relay but the board diagram would show an airwire on the "right" side of the relay? 

On 24/09/14 19:02, auarduino wrote:

Thank you for the response.  I am very new to electrical designs and

schematics and you bring up some good points. 

 

It did really bug me and I spent a long time trying to get the two to

look the same.  Also, is this the same reason why sometimes I would

connect a net to the contact on the "left" of the relay but the board

diagram would show an airwire on the "right" side of the relay? 

 

Yes and no.

Because the schematic is concerned with function, the symbols often put

inputs on the left and outputs on the right, as this helps

understanding. The physical components may be arranged quite differently

for packaging reasons.

In the case of relays, though, the coil is usually not directional

(although some do have built-in flyback diodes) and the contacts are

simply switches. It's common for the library symbol to show the coil on

the left and the contacts on the right, because of the input-to-output

thing. It's also common for the contacts to be drawn with the N/O pin

nearest the coil, because that makes it look like the coil "pulls" the

switch over. The physical relay may well be designed with a lever or

pivot, so that the contacts end up the other way round (the coil pulls

down on the top arm, which pivots around the bend and pushes the

contacts away from the coil).

You should train yourself out of the desire to make the schematic and

board "look the same". They never will, and it's far more useful to lay

out the schematic to clearly represent function. Design your initial

schematic with no regard for the packages at all (some EDA tools

encourage this by completely separating the two editors, Eagle keeps

them together but you don't need to create a board at all until you've

got a nearly ready schematic).

HTH,

Rob

Good to know.  Thanks again for the detailed response.  Do you have any other comments/suggestions/tips  for someone knew to the world of electronic designing (predominately hobbyist designs)? 

I am marking your first response correct as it answered my question.