Electronic – Controlling external appliances with a microcontroller by replacing switch with relay

microcontrollerrelayswitches

I am working on a custom school project where I want to control a coffee machine's power using a micro-controller.

I have never worked with interfacing to external appliances like this before so please bear with me as I describe my question.

My idea for this problem is to replace the switch with some sort of relay configuration, in order to control the power flow with my micro-controller's output. I've done some research and believe I am working with an SPDT switch. It has 3 pins, the first pin connected directly to the power line, the second pin connected to a heating element, and the third pin connected to the heating element and ground.

I've also found a relay at my local store that I believe should work (please tell me if I'm wrong). It can be found here: http://www.alliedelec.com/search/productdetail.aspx?SKU=70133525.

I am able to produce a 5V output from my micro-controller which I plan to use as the control signal for the relay.

This being the first time I've worked on this type of application, I want to make sure I understand how to transfer the wires from the switch to the relay correctly before I go about testing my configuration.

Here's the coffee machine's switch and wires:
coffee machine wiring

and here is the relay's schematic:

relay schematic

From what I understand the wiring should be as such:

  1. Single black wire (top pin of switch)
  2. Black and blue wire (bottom pin of switch)
  3. Control signal from micro-controller (providing 5V)
  4. Red wire (middle pin of switch)
  5. Ground (provided by micro-controller)

Would this configuration be correct? Please let me know if I should try anything else or if any additional information is needed.

Best Answer

Based on your picture and the wire colors I see, I have a question. Does the switch light up when the coffee pot is turned ON? If so, what you have is a SPST (Single Pole Single Throw) switch with built-in indicator.

The blue wire is usually neutral and the brown wire is usually hot or live. The middle switch terminal is usually the common point of the switch and the indicator.

Because this is a coffee pot, expect some significant current. The solid-state relay that Some Hardware Guy showed a picture of is a good choice. Be aware that it probably requires a heatsink. Pick the heatsink size by assuming that the SSR will drop 1V at whatever current your load consumes.

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