Help with Making a RPM tacho Shift Light circuit open a 12v Relay

Please allow more specifics. Like.

What are you needing out of the relay. (12V 1A)?

SPST or DPDT?

If so, here is an idea. Remove the led, replace it with a solid state relay, And replace the led off of the relay load side of the circuit.

Off the top of my head here is a relay that may work. But you will need to look around and see if this will fit your needs.

You may need a DPDT, or something handling more power, etc.

But let me know what you think of this solution.

It may also be possible to use a low voltage (On the input) solid state relay , this would provide isolation and an easy interface ?, optionally an opto isolator in series or replacing the LED in question with same result

Peter

Thankyou for your replies,

I have a fairly good understanding of simple electronics and some more technical things but IC's and this style circuit are still new to me.

I didn't understand this circuit and what the led was actually doing.

when i tested it with a multimeter and connecting between the pos or neg pins on the led i was always getting voltage even when the led was off just when the shift light was turned on i was getting more.

I only need a spst relay on it and about 1-2 amps would be max if i needed more i could run a larger relay off that one anyway.

i tried unsoldering the led and running a relay off the same pins but it didnt work because it wasnt turning it on or off and of course the voltage at the pins is 3.5v for the blue led so unless i can get a relay that has a 3-5v turn on then can handle 12v through?

hope this helps a little sorry for my lack of knowledge 

the LED drivers will not have anything close to the power needed to turn on a relay, you will need to use an opto isolator or at least a transistor to do the job

See this for a bit of a backgrounder http://www.element14.com/community/groups/internet-of-things/blog/2014/08/05/drive-big-things-with-added-safety-opto-isolators

the LED drivers will not have anything close to the power needed to turn on a relay, you will need to use an opto isolator or at least a transistor to do the job

See this for a bit of a backgrounder http://www.element14.com/community/groups/internet-of-things/blog/2014/08/05/drive-big-things-with-added-safety-opto-isolators

I checked out your link Peter.

I have also tried to use a transistor on the led leg without any success. I wasnt sure what i exactly needed or what would work. When testing i know it always had voltage between both pins of the leds and their opposing supplies.

For example when i tested the voltage between the pos pin on the led and the ground i got a voltage and then the same thing happened between the neg pin on the led and the positive supply even when the led was turned off yet no voltage between the led's pins themselves.

I think from memory the negative pin was earthed straight to the negative so must have some form of positive change when reaching the desired rpm from the frequency- voltage chip.

so if it is a "switched positive" is there a particular type of npn transistor i need to use or is there a huge range that would work?

Thankyou.