changing 12v dc

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spaspecker

Copper - Posts: 59

Joined: September 07, 2006

Location: United Kingdom

Posted: January 09, 2008 at 4:50 PM / IP Logged

not sure if i'm in the right section so apologies in advance if wrong.

how would I change 12vdc to another voltage? reason for question is a potential project requires the use of an illuminated pushbutton, the illumination is by way of a LED that uses 1.6v dc, but my power supply is 12v dc.

how do I "stepdown" 12v dc to 1.6v dc

thanks in advance

tedmond

Gold - Posts: 4,610

This member has been recognized as an authority in Mobile Security and Convenience. Click here for more info.

Joined: January 06, 2007

Location: Ontario, Canada

Posted: January 09, 2008 at 8:34 PM / IP Logged

use a voltage regulator.

i am an idiot

Platinum - Posts: 13,667

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: January 09, 2008 at 9:07 PM / IP Logged

A 1K resistor should do the trick. If there is a ground wire on the switch it's sole purpose is to supply ground to the LED. You can insert the 1K (1000 Ohm) resistor in series with the ground wire.

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: January 09, 2008 at 9:24 PM / IP Logged

A resistor won't drop the voltage, but it will limit the current which should protect the LED from damage.

A voltage regulator would be the best way to actually convert the voltage, but overkill for a simple LED. They make adjustable voltage regulators where you can select the output with a few components.

What kind of illuminated push button are you using?

Kevin Pierson

spaspecker

Copper - Posts: 59

Joined: September 07, 2006

Location: United Kingdom

Posted: January 10, 2008 at 3:42 AM / IP Logged

my idea is to use this button as a start button in my car:

http://cpc.farnell.com/jsp/search/productdetail.jsp?sku=SW02731

i already have a start button wired in, but i want to change it for one that illuminates. it says that the forward voltage for the LED is 1.85v dc, so i know i can't feed it 12v

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: January 10, 2008 at 8:09 AM / IP Logged

I would throw a 750 ohm resistor on there and be done with it. As long as you keep the max current below 20mA you shouldn't have to worry about the voltage difference.

Kevin Pierson

spaspecker

Copper - Posts: 59

Joined: September 07, 2006

Location: United Kingdom

Posted: January 10, 2008 at 12:28 PM / IP Logged

not sure what's going through it, current button is wired like this:

30: +12v constant

87: starter motor

85: +12v ignition (switched)

86: one side of momentary switch, the other side to ground

but I'll try the resistor suggestion

tedmond

Gold - Posts: 4,610

Joined: January 06, 2007

Location: Ontario, Canada

Posted: January 10, 2008 at 3:16 PM / IP Logged

you got that relay wired up wrong. do you plan to allow start on the push only? or with key as well?

if just with push button

85 - 12v @ ignition harness

86 - to push button (ground push button)

87 - high current 12v

30 - to starter wire on car. (motor side)

if you wish to start using key and using push wire it up like so

85 - 12v @ ignition harness

86 - to push button (ground push button)

87 - high current 12v

87a - starter wire (key side)

30 - starter wire on car. (motor side)

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: January 10, 2008 at 4:02 PM / IP Logged

His way would work with or without the key. There is no need to isolate the starter wire from the switch - the switch rests in the open position anyway, so there is no need to cut the starter wire.

I have my pushbutton start installed just like in his (30 to high current 12vdc, 87 to starter wire) and it works great.

Kevin Pierson

tedmond

Gold - Posts: 4,610

Joined: January 06, 2007

Location: Ontario, Canada

Posted: January 10, 2008 at 10:36 PM / IP Logged

sorry pierson is correct. not enough concentrain ahah. Guess im too worried about my rolled ankle that i got from doin my sports; it hurts gah well thanks for correcting me.

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changing 12v dc

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