Hi people and many thanks for taking time out to read my request for help with a Relay Shield project.
I’m using my Spark Core and Relay Shield to switch some mains powered lamps sitting in our office. I’ve got everything set up and working nicely and we have a little web service that let’s people change pin states using a function exposed to Spark Cloud.
One problem I am having is that when the web service loads it does not know the current state of each pin. I want to create a new function, or a Spark.variable, that outputs the state of each pin, as a STRING array: “HIGH | LOW | HIGH | HIGH”, for example.
I’m having difficulty wrapping my head around the Variables because I can’t find much in the way of documentation. I can think of some long winded ways around this but in the interest of streamlining the code I am in the market for some advice.
Has anyone done this for another project they can point me to? If not, does anyone have suggestions?
Assuming you want multiple people to control the device at the same time, I wouldn’t go with variables. Variables is a polling process, and is not very friendly when it comes to real time information, unless you poll every second, which is a waste of resources. I’d rather store the states of the pins on the Core, and use a Server Sent Event to publish the values as soon as one changes. This has the benefit of only using resources when something happens, as soon as something happens. Since this doesn’t require action on the client side, those can be updated real time, without needing to poll repeatedly.
To get the initial values when opening the web page, you could create a function that publishes the values, which gets called as soon as the page is loaded. I’m currently using this for my RGB lighting project, and it seems to work fine so far
Let me know if you need any help, and I’ll see what I can do.
Hi @Moors7 and thanks for getting back to me with your suggestion. I’ll have a play today and see if I can work it out, and come back to you if (or more likely when) I get stuck. Thanks again.
You might want to look at this thread where I helped another user with his relays controlling aquarium pumps. Both firmware code for the core and HTML are provided. For this application, the user wanted the durations in seconds rather than minutes or hours:minutes, but it could be easily changed.
I’d hoped the use some of the logic from the link @bko passed on, whereby I have an array (int relayState[4] = {LOW,LOW,LOW,LOW} and a function that loops through the four relay pins and assign a value (HIGH or LOW) to each position in the array, and then I’d hoped to output that to my web service.
Does that make sense - I have to confess that I’m an eager learner but have basic knowledge so might be trying to do something very naive here.
I’d probably go with @Moors’ solution. Something similar to:
Have your core emit an event every time a pin changes. This event’s data would simply be that binary number I mentioned.
Have a function which, when called, emits the event and then perhaps returns the binary number itself as the return value.
I said it was hackish because POST calls aren’t really supposed to have to return a value (other than success or failure). You can leverage the fact that it does but it just feels a little “dirty” to me.
You could also make the event data structured as JSON for easy parsing on the receiving end, but I’m not sure if that’s necessary. The binary data should suffice.
and a function that loops through the four relay pins and assign a value (HIGH or LOW) to each position in the array, and then I’d hoped to output that to my web service.