Help with relay drive zero crossing

[Nicholas]

zero crossing relay

Can I use only one Input pin on MCU to implement zero crossing for relay drive?
I used this pin as mains frequency signal input for now , and do relay drive in a fixed delay time after detecting zero crossing . But cause relay response time varies from one to one , so , a fixed delay time can always work , so , any more good solution ? only one I/O left , no more.
Hope anyone help. thx.

 

[Ace-X]

Just use triac output driver, like MOC3082 and any suitable triac, for example BT139. You will need just one pin for output - the whole zero-crossing functionality will be provided by MOC.

Ace-X.