relay problem for your Arduino projects

It is often found relay terminals work in opposite way. Normally Close actually works as Normally Open. Normally Open becomes Normally Close. If this happened to your relay, you had a "Active Low" relay. You can swap wiring to solve the problem.

有人拿到繼電器後, 發現"常開"和"常閉"接頭居然是相反的....其實是誤解。有些繼電器是低電平觸發, 也就是接到LOW訊號的時候才動作!!