Recently we at @ttncat had to prepare a crash course on LoRa, LoRaWAN and The Things Network for a professional school in Barcelona. It was a 15 hours course that covered from the very basics to some more advanced topics on RF like link budget, attenuation or impedance matching. It was fun to go back to my years at college and revisit and update some of those topics. And at the same time it was a great opportunity to upgrade my toolbox.
I’d like this to be the first of a series of posts about radio frequency. Talking about tools and devices I already had and some of the new ones I now own. I think they might be of some interest for newbies and makers since -due to my budget- they tend to be low cost devices. At least I hope you will find it interesting to know they exist.
I don’t pretend to write these posts in any specific order but I’m just starting with what I feel is one of the most basic concepts, and it’s that a radio device outputs energy. So maybe one of the first questions is “how much energy?“.
So RF power monitoring is the first step to analyze how a certain radio sends data by quantitatively measuring how much energy it outputs. You probably know this is called “power” and power is measured in Watts (W). Radio Liberty (a CIA-founded organization meant to broadcast anti-comunist propaganda) had a facility in Pals, Girona, from where they could reach as far as Moscow. The facility consisted on 6 radio towers with an overall output of 1.5MW (that’s megawatts).
It’s not that other Sonoff products are not “serious” business, but there are a number of design changes in the Sonoff S31 that make this new product a world apart. For the functional point of view it looks like a S20 with POW-powers, but they have redesigned the product completely. The result is very very interesting.
Revamped case, more compact and sturdy
Redesigned PCB, actually 2 different PCBs for main and control
Different power monitor chip: the CSE7766 (same as in the new POW R2) replaces the HLW8012
The only drawback: it’s only compatible with plug types A & B, tat is central and north-america and few other countries. I’d love to see a S31-EU schuko version!
You can buy the S31 from Itead (see link above) or via the usual marketplaces. Actually the S31 is slightly cheaper [Ebay] on some of them.
A few years ago (not many) I used to burn copper plates using acetic acid, a.k.a. vinegar. I was somewhat concerned about using stronger acids so it was OK to use another acid, even if it was soooo sloooow. If you were patient you could get to have decent boards using 50mil traces (or even thinner). But it required keeping a good temperature on the copper bath and regulating the ratio vinegar/hydrogen peroxide continuously, adding a little salt from time to time to speed things up.
The vinegar biting the copper
One day I saw an article about cheap Chinese PCB fabs (I think it was DirtyPCB by Dangerous Prototypes) and I decided to design my own board and send it to fab. I used Eagle (I still use it although I’m learning KICAD) and the learning process was significant. But at the end I managed to get something. I learned to use copper pours, to correctly label the board, to create my own parts, to avoid auto-route, to use design rules and create gerbers,…
And over time I have tested different fabs. I’m not an expert by any means but I wanted to write a bit about them here. The basic order I usually do is a 10 units, under 50x50mm board, 1.6mm thick, 1oz copper and HASL Lead Free due to RoHS rules in the EU. The prices and options below are based on these settings.
One more thing. I reckon these suppliers are good enough in most cases for small batches, testing boards or DIY projects. Some EE are concerned about the quality of the boards and they prefer EU-based (or US-based) fabs. I cannot offer a good reason to use these manufacturers here or to not use them in professional/industrial projects.