The version 2 boards came back. This design has the SSR and button power system so that there is no standby load. One thing I discovered while the boards were being made is that the Tiny9 has a Vcc Level Monitor system (again, why they don't call it a brownout detector, I'll never understand). At first glance, it doesn't seem terribly helpful, as if you configure it for the "high" RESET voltage (VLM1H) is "typically" 1.6 volts, while the safe area curve for the chip bottoms out at 1.8 volts (the VLM1L threshold is even lower at 1.4 volts typical). Why they made this choice I can't understand. However, in practice it appears to work ok (at least for one example). When the timer runs out, the SSR is dropped and you can see the power LED fade out over the course of about a second as the power supply filter caps bleed out. If the VLM wasn't working, I'd expect the chip to reset as the voltage dropped, and of course the first thing the firmware does is turn the SSR back on.

So it appears that we don't actually need a hardware voltage watchdog chip separate from the VLM in the Tiny itself.

The upcoming v3 board makes another change, and will likely be the final version. In this one we've traded a second SSR for a cheaper open-frame DC power supply that's rated for only 1 watt. The second SSR switches a power load on the AC side. 3 10kΩ 2W resistors form a ~4.3 watt RMS load (at 120VAC). The DC load (both SSRs and the power LED) top out at about 600 mW (the controller load is negligible). The power supply is supposed to be about 60% efficient, so that's another watt of load, so the combined total should be plenty to fool the Intelliflow.