Some months ago, I found that my measurements of energy flow were being adversely affected by the use of the RFM12 module. Every time that an RF message was transmitted, the accumulated energy value dipped by around 10 Joules.
I made a video clip of this at the time but for some reason never made it public. I'd forgotten all about this strange effect until today when I came across the video which is at https://www.youtube.com/edit?o=U&video_id=a2Oi4afhrh0
[Edit: Sorry, I meant https://www.youtube.com/watch?v=a2Oi4afhrh0 ]
Any ideas what might be going on here?
Re: Energy measurements being affected by RFM12B
I think you need to edit your video link, use the sharing link.
This looks like your own account's edit link so no one else can see it (it just takes me to my own YouTube videos)
Re: Energy measurements being affected by RFM12B
Sorry, that link doesn't look right. Maybe this one will work:
https://www.youtube.com/watch?v=a2Oi4afhrh0
Re: Energy measurements being affected by RFM12B
Did the accumulated energy drop by 10 J, or did it accumulate 10 J less than you expected it to? The reason I put it that way is my first suspicion is the supply rail, hence the analogue reference, is being affected by the extra load when the RFM12B transmits.
Re: Energy measurements being affected by RFM12B
The former. With a 40W bulb, the expected increase in energy level per mains cycle is less than 1 Joule.
After making that video, I recall changing the sketch so that the LED only illuminated if the energy level dropped by greater than N Joules between one mains cycle and the next. To prevent the LED from flicking on whenever an RF message was transmitted, the value of N had to be around 10.
If anyone is interested in following this up, I still have some hardware on which that test could be repeated. I can't remember what the sketch was called but it will no doubt be kicking around somewhere ...