Using Node Red to Control the MCP23008

Now that we have our MCP23008 configured, we need to be able to use it. Node-red comes with a really handy node for testing things just like this, it’s called “Inject”. Let’s drag it over and set it up to control a relay.

There is a dropdown on the payload field you should use to select “09 Number” to define it’s a numeric payload, set the payload to 1. To control an individual channel, the topic of the message should be channel_{n}, in this case we’re just going to control channel 1, so we’re going to set the topic to “channel_1”.

I’ve given it a name of “Turn on Relay 1” and click Done. Since we may, at some point, need to turn this relay off, I’ve made a copy of the node (select the node and click cmd+c on mac, or cntl+c on windows, then cmd+v or cntl+v) and changed the payload of the copy to 0, and the name to “Turn off Relay 1”.

Once you’ve done that, drag the outputs of those Inject nodes over to the input of the MCP23008 node.

Now we can control the relay, but what if we need to act on a status change? Another node that gives us an easy way to see messages moving through the flow, is the “Debug” node. Grab one and move it to the right side of the MCP23008 node. By default, this node will print the payload of any message it receives to the Debug pane, since this is exactly what we want, all we need to do is drag the first output of the MCP23008 node over to the input of the debug node.

Your flow should now look something like the screenshot on the left. If it does, click on the “Deploy” button on the top right of the window.

All of those little blue dots will go away, indicating that your flow is up and running, and you can start testing! Click on the buttons next to your Inject nodes to turn your relay on and off, the debug window should show you a 1 or 0, respectively, whenever the relay status changes.