Help - need to a circuit to trigger relay

[5neaker]

Hi

can someone help me. I need a circuit that will trigger an output to a relay when it get a predefined input voltage

input voltage - 3.19 volt, will be using ground to measure this input voltage

Any help would be greatly appriciated

Ray

 

[nettron1000]

Sounds like a good application for a comparator circuit. Heres a link to some info and schematics.

**broken link removed**

 

[Russlk]

Note the diode across the relay solonoid coil, that is needed to protect the IC output from the inductive kick when the relay is turned off.

 

[Agent 009]

You could just implements a diode limiter circuit... I can\t draw you a schematics right now, but as soon as I get my hand on my PC, I'll post it. By the way, how does your input looks like? Is it a 3.19V DC?

 

[Dialtone]

Do a google search for datasheet on ULN2803. The ULN28xx family is an octal darlington pair driver well suited for driectly driving relay coils over a broad voltage range and fairly hefty power outputs from a DIP package. No need to build from discrete components when a perfectly good IC package exists than can do 8 for the price of 1.
Dialtone

 

[pike]

I would go and use something like a zener diode in series with a voltage dropping resistor to trigger a transistor, which then triggers the relay