Wouldn’t the easy way be not with emonHub at all, but do it all in the front end - transmit the data that’s destined for the Pi at the same time that it’s sent via the serial link?
Yes that would be the more direct way, but I think it should be possible to achieve it with emonhub without having to modify the emonpi firmware and to make sure its a feature that you can enable rather than have the emonpi transmit all the time.
Anticipating a question, would the emonPi transmit only it’s own data (plus of course the time, if required), or would/should it retransmit any received node’s data, or only selected nodes?
(My thinking - if a sensor node is within range of the base, but out of range of the GLCD.)
Prior to being emonpi’d emonhub had everything in place to send values out via a connected RFM69Pi or emonPi, I do not know if that is still intact or to what degree.
That’s quite limiting in it’s flexibility and quite difficault to use. If sending via emonhub you can pipe pretty much any info, for example summing multiple PV arrays or determining “use” from “pv” on one device and “grid” on another, plus if any “adjustment” (aka calibration) is required etc etc. It was intended that a emoncms interfacer could query any array of feeds from emoncms (using the fetch api) but the current emoncms interfacer doesn’t do that. For an immediate solution a simple script could be set up to query the data from emoncms (or somewhere else) and via a emonhub socket it could be transited via the emonPi or RFM69Pi.
Although the current emonGLCD sketch would need editing if you wanted to have other stuff like “diverted” or “ev” etc, it would be nice to be able to rotate the data like on the emonPi lcd.
@Stuart wrote a modified Jee interfacer for emonhub to allow sending of text names as well as values to a Nokia display from emonhub using JeeLib, that way you could tell the display what to label the data you decide to send it without having to upload a new sketch (if the emonglcd would permit such a thing, I know resource is short). (see emonNOTIFY - remote visual monitoring device by stuartpittaway · Pull Request #39 · openenergymonitor/emonhub · GitHub)
I was my intention that emoncms data would be transmitted or published in this way, I also wanted to drive the emonpi glcd direct from emonhub too, so that custom labels and values could be displayed.
I’ve not checked, but I think there are some functions in many emonGLCD sketches that could go, as at least some of the functionality is repeated in emonCMS. Whether that would free enough memory - I don’t know.