An Introduction to Solid State Relays

When we think of relays, we tend to think of those big mechanical things that make a satisfying ‘click’ when activated. As nice as they are for relay-based computers, there are times when you don’t want to deal with noise or the unreliability of moving parts. This is where solid-state relays (SSRs) are worth considering. They switch faster, silently, without bouncing or arcing, last longer, and don’t contain a big inductor.

Source Fotek SSR Specifications Sheet

An SSR consists of two or three standard components packed into a module (you can even build one yourself). The first component is an optocoupler which isolates your control circuit from the mains power that you are controlling. Second, a triac, silicon controlled rectifier, or MOSFET that switches the mains power using the output from the optocoupler. Finally, there is usually (but not always) a ‘zero-crossing detection circuit’. This causes the relay to wait until the current it is controlling reaches zero before shutting off. Most SSRs will similarly wait until the mains voltage crosses zero volts before switching on.

If a mechanical relay turns on or off near the peak voltage when supplying AC, there is a sudden drop or rise in current. If you have an inductive load such as an electric motor, this can cause a large transient voltage spike when you turn off the relay, as the magnetic field surrounding the inductive load collapses. Switching a relay during a peak in the mains voltage also causes an electric arc between the relay terminals, wearing them down and contributing to the mechanical failure of the relay.

Continue reading “An Introduction to Solid State Relays”

Hackaday Prize Entry: Another Internet Button

It’s long been a staple of future-gazing, the idea that we will reach a moment at which all of life’s comforts can be summoned at the press of a button. Through the magic of technology, that is, without the army of human servants with which wealthy Victorians surrounded themselves to achieve the same aim.

Of course, to reach this button-pressing Nirvana, someone has to make the buttons. There are plenty of contenders for the prize of One Button To Rule Them All, the one we’ll probably have seen the most of is Amazon’s Dash. Today though we’re bringing you another possibility. [Hendra Kusumah]’s A.I.B. (Another IoT Button) is as its name suggests, a button connected to the Internet. More specifically it’s a button that connects to IFTTT and allows you to trigger your action from there.

Hardware wise, it couldn’t be simpler. A button, a Particle Photon, some wires, and a resistor. Then install the code on the board, and away you go. With a small code change, it also works with an ESP8266. That’s it, it couldn’t be simpler. You might ask where the fun in that lies, but you’d be missing the point. It’s the event that you trigger using the button that matters, so why make creating the button a chore?

We’ve shown you many IoT buttons, just a couple of posts are this ESP8266 button and a look at  the second-generation Amazon Dash.