• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Micros - Relays Logic ?

Status
Not open for further replies.

Wp100

Well-Known Member
Hi,

Just interested to know why many of the mechanical and SSR relay boards now coming out of the Far East feature Active Low Logic as against the more usual Active High Logic.

Thought there must be some commerical reason for this change around , though as many micros ports seem to power on default to zero, a bit puzzled why ?
 

schmitt trigger

Well-Known Member
What Pommie said...
.......and it is also easier to drive from a different voltage level (i.e. 12 volts) with a simple NPN open collector. There are several IC drivers which feature arrays of NPN open collector outputs, allowing significant integration.

But you are correct.... With the default to zero of microcontrollers, one of the first instructions to be executed would be to set the ports high.
 

Wp100

Well-Known Member
Hi,

Many of those relay modules come with transistor or opto coupler inputs so current drain from the micro is minimal.

Just that after so many years of driving relays/SSR High, these board have changed to Low, surely for a reason ?


001192.jpg001193.jpg
001191.jpg
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top