Open collector for a dummy...

[alpina165]

Hi folks,

I'm trying to build something that operates a siren via a relay when a countdown timer reaches zero.

I've built the following two kits for the timer and relay
4-digit Timing Module with 6 Optional Functions (3148)

**broken link removed**

My question is, how do I use the open collector output of the timer to operate the relay?

 

[BrownOut]

To get a logic level from an open collector, just connect a pullup resistor of, say 10K ohms. As long as the resistor supplies the required current to your circuit, you're good to go.

 

[alpina165]

Sorry I did say I'm a dummy! where does the pullup resistor connect to?

 

[BrownOut]

To your positive supply voltage wire.

 

[alpina165]

Got it! I think.

Many thanks

 

[BrownOut]

Double check the current requirement at the input of your relay board and make sure the 10K resistor will supply enough current R = V/I, R is your pullup I is the input current, and V is the low limit for a logic high. You may find you have to lower the value of your pullup.

 

[BrownOut]

PS: Your resulting logic level is gonna be inverted. When the output transistor is "ON" your level will be low, and visa-versa.

 

[alpina165]

All working perfectly now, thank you very much for your help.

 

[BrownOut]

Glad to help.