The Low-power Supply described previously on this weblog now has a PCB – and it’s about as small as a JNµ:
Here’s an assembled unit, ready for testing and hooked up to power a JeeNode (w/ disabled bootstrap):
And here’s the whole test setup I had to create to check this thing out:
Lots of stuff involved, including high-voltage probe and 230V isolation transformer (to the right, out of view).
Here’s a demonstration of how it works – summarized as one elaborate scope capture:
Green is the mains voltage (235 Vrms), purple is the charge building up on the 100 µF reservoir capacitor, yellow is the regulated output, and blue is the JeeNode’s current consumption (measured as voltage drop over 10 Ω). Note how some of the voltages measured here differ more by than four orders of magnitude!
Anyway, that zoomed-in image is the clear signature of the second 8-byte RFM12B packet transmission. Current consumption varies from 23 to 26 mA. It’s a relatively coarse image, since it has been zoomed in 4,000 times.
The 3.3V supply level is reached ≈ 2s after power-up, with another 2.5s needed to fully charge the reservoir cap. You can see from the purple dips that this supply could sustain at least one packet transmit per second.
No surprises here, but it’s good to see that the PCB design works as intended. Next step: implement deep sleep on the ATtiny84 – hopefully this’ll take just some minor adjustments to the Sleepy::loseSomeTime() code.