0-10v Analog to Digitial

Im looking for something that converts a 0-10v analog signal to a digital that activates a relay.

The long story is,
I have a ventilation controller that puts a 0-10v signal out, depending on temperature, humidity and a couple other factors. I've used up all the relays that it has and I can use an analog output but i need something that converts the lets say 5v signal and turns on a relay. Is that possible in any way?

Thanks for the help.

Use a voltage divider to map the 10V range into a 5V output, suitable for the Arduino analog inputs.

Add a safety factor (3V output range instead of 5V), caps, clipping diodes and more, as required for the ventilation controller signal.

Why do you need an Arduino for this? Sounds like a job for a simple analog comparator.

Why not just add more relays to the existing ones?
Eg use one of the existing relays to switch on other relays.

Daz

Or just a simple NPN transistor. 10V on the base (thru a current limit resistor), collector pulls the relay coil 'output' low to energize it.

CrossRoads:
Or just a simple NPN transistor. 10V on the base (thru a current limit resistor), collector pulls the relay coil 'output' low to energize it.

Nope. The OP wants a relay to close at a specific analog output level from his analog controller. DrDiettrich provided the solution in first reply. Any basic Arduino with analog inputs will do the job outlined provided the controllers 0-10V output is reduced with a 1:1 voltage divider to bring the signal into range for the Arduino.

Analog comparator does such a job just fine (use a pot on the other input to set the actual desired switch over level). The main problem I see here is the lack of hysteresis.

Just thinking of the hysteresis problem: voltage divider using a fixed resistor and a pot + 5V Schmitt trigger + clamping diodes to protect it from >5V on the inputs should settle that.