Haynes Forums  

Go Back   Haynes Forums > Haynes Roadster Forums > SVA/Legal
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #11  
Old 19th June 2013, 02:35 PM
skov's Avatar
skov skov is offline
Senior Member
 
Join Date: Jan 2011
Posts: 1,085
Default

Quote:
Originally Posted by CTWV50 View Post
I could do with details on that too John, guess it involves a relay and a piezo. I'm guessing?
You guess right!

This is more or less what I've ended up doing:



Prior to that I just had the switch
Reply With Quote
  #12  
Old 19th June 2013, 05:26 PM
CTWV50's Avatar
CTWV50 CTWV50 is offline
Senior Member
 
Join Date: Aug 2010
Posts: 1,297
Default

Quote:
Originally Posted by skov View Post
You guess right!

This is more or less what I've ended up doing:



Prior to that I just had the switch
Wow! I didn't think it would be that complicated, I don't understand. Wouldn't the buzzer just buzz all the time when the fog light is on? Or does the 1 amp diode some how stop it buzzing! Ehh I feel thick! Why is the relay at the bottom not doing anything? No I'm confused! lol!
Reply With Quote
  #13  
Old 19th June 2013, 05:31 PM
CTWV50's Avatar
CTWV50 CTWV50 is offline
Senior Member
 
Join Date: Aug 2010
Posts: 1,297
Default

Oh I see now the electric current passes through the diode when the ignition is switched off and the fog light switch is on because it then becomes the path of least resistance? Am I right?? I'm not, am I? ....Doh!
Reply With Quote
  #14  
Old 19th June 2013, 06:47 PM
SeriesLandy's Avatar
SeriesLandy SeriesLandy is offline
Senior Member
 
Join Date: Nov 2008
Location: Portsmouth
Posts: 828
Default

When the ignition is on the buzzer has 12v at either side, when the ignition is off (0v) it will buzz as that's the earth.
__________________
Steve
My Photo Album | Haynes Roadster FAQ | IVA Forms How To
Reply With Quote
  #15  
Old 19th June 2013, 07:33 PM
CTWV50's Avatar
CTWV50 CTWV50 is offline
Senior Member
 
Join Date: Aug 2010
Posts: 1,297
Default

Quote:
Originally Posted by SeriesLandy View Post
When the ignition is on the buzzer has 12v at either side, when the ignition is off (0v) it will buzz as that's the earth.
Mmmm I still don't get it but I started looking at relay stuff and ended up coming up with this....



Would that work? Other than the fact I'm probably drawing too much curent through the 1st relays coil to power the fog but another relay would solve that. Or am I way off track?
Reply With Quote
  #16  
Old 19th June 2013, 09:04 PM
skov's Avatar
skov skov is offline
Senior Member
 
Join Date: Jan 2011
Posts: 1,085
Default

Quote:
Originally Posted by CTWV50 View Post
Would that work? Other than the fact I'm probably drawing too much curent through the 1st relays coil to power the fog but another relay would solve that. Or am I way off track?
In a word, no
You're right - the fog won't light up because it won't get enough current through the coil of the relay.
You could add a third relay, but you'd be over complicating it a bit!

You can completely ignore the second relay on my circuit. I only needed that because I'm using a switch with a built in LED.
If I was doing it from scratch I'd use a seperate warning lamp wired in parallel with the fog light.
So without that my circuit looks like this:



So... if you ignore the buzzer and diode first. When the switch is on it turns the relay on. If the lights are on the fog gets power, it they're off it doesn't. Simples.

Now, ignore the relay and fog light and just look at the switch, diode and buzzer.
When the switch is on and IGN is on, both sides of the buzzer are at 12V, so no current flows through the buzzer and it stays off.
When the switch is on and IGN is off, the + side of the buzzer will be at 12V and the - side will be at 0V. So current will flow through the buzzer and it will sound.

The diode is needed to stop current flowing from IGN through the buzzer and relay coil when the fog switch is off and IGN is on.
Reply With Quote
  #17  
Old 19th June 2013, 09:49 PM
CTWV50's Avatar
CTWV50 CTWV50 is offline
Senior Member
 
Join Date: Aug 2010
Posts: 1,297
Default

Ahh I see! You are quite brilliant. One question though! Why does the piezo buzz if a circuit isn't made to the negative side of the battery?
Reply With Quote
  #18  
Old 19th June 2013, 09:50 PM
twinturbo's Avatar
twinturbo twinturbo is offline
Super Moderator
 
Join Date: Jul 2008
Location: Carlisle
Posts: 4,389
Default

Quote:
Originally Posted by skov View Post
When the switch is on and IGN is off, the + side of the buzzer will be at 12V and the - side will be at 0V. So current will flow through the buzzer and it will sound.
Only if the ignition switch changes from live to ground , most will change from live to unconnected not ground.

TT
__________________
You only get a woosh with a dump valve

Build Thread


Man Cave Mantiques



Cecil Street Auto Repairs Garage Carlisle




Build Cost £4181.65 - Last - Wheel Cylinders
Reply With Quote
  #19  
Old 19th June 2013, 10:45 PM
skov's Avatar
skov skov is offline
Senior Member
 
Join Date: Jan 2011
Posts: 1,085
Default

Quote:
Originally Posted by CTWV50 View Post
Ahh I see! You are quite brilliant. One question though! Why does the piezo buzz if a circuit isn't made to the negative side of the battery?
Quote:
Originally Posted by twinturbo View Post
Only if the ignition switch changes from live to ground , most will change from live to unconnected not ground.

TT
Ah ha, you've both discovered the slightly dubious subtlety in my scheme

It's correct that IGN is typically switched from battery to unconnected.
However, there are going to be several things on the car that are powered off IGN.
These will be connected between IGN and GND, and effectively drag IGN down to GND when it's switched off.
The buzzer will sort of leech current through these loads, which is the dubious part. However it requires so little current that it gets away with it...
Reply With Quote
  #20  
Old 19th June 2013, 11:15 PM
CTWV50's Avatar
CTWV50 CTWV50 is offline
Senior Member
 
Join Date: Aug 2010
Posts: 1,297
Default

Those electrons are trickey little buggers!
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 06:06 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.