After the last time, I've added the following features / bugfixes to my project
- Added button handling; one button to reset egg temperature (if inserting new eggs), the other to switch between showing water temperature and egg yolk temperature
The button functionality already existed, but I had tho remap it to other pins, and add some wrapper functions - Added buzzer output (controlling the VOUT2 of the LTC3108). When the egg yolk is above (calculated) 85degrees celsius, three beeps are generated.
- Removed a lot of deprecated code
- I've added some more capacitors to VSTORE.In my application, a lot of energy is generated while heating up the pan. When the pan has heated up, not much energy is harvested anymore, also due to placement of the heatsink / radiator. More convection would have been possible when the generator is placed on the side of the pan (air would be flowing due to heat of the pan), but I didn't want to risk placing the radiator in the fire of my stove... The VSTORE pin can charge a capacitor bank when ample energy is provided, and this capacitor bank is drained when no input power is present. Increasing the amount of capacity on this pin will not deteriorate the startup time (it will just take longer to have enough 'spare energy' to power your converter)! For my application this is ideal; at the beginning I have ample of energy, that I want to use much longer than the heat under the water is on. With my 'solution' you can also save energy by using less fuel to cook your eggs!
Alternative take on getting the harvester going
With my hardware and software working (YEAH!) I decided to quench my thirst for better harvesting solutions to try a different approach on getting the harvester going. In my previous post (Building and debugging my harvester - Part 4) I found a way to start my board by switching on the non-harvesting part only after the 3V3 caps have been almost fully loaded. That is a working solution, but I thought I might give another option a try, and that was to use the VLDO output of the LTC3108 to power the microcontroller. This pin is, according to Linear, suitable for powering a microcontroller, and that would be a really nice approach; the EFM32 would run at a lower voltage, thus using less energy, I could power the LCD controller in the GiantGecko either from its internal boost converter or from the LTC3108, and I wouldn't have to make a comparator + FET patch. I thought it might work because the supply immediately starts charging the on-board capacitors, so there's no 'draining' of supplies, as I had with my original design (see application note AN0062 from Energy Micro for more backgrounds).
Unfortunately it didn't work. I had a spare PCB to populate, and on that PCB I built the harvester and the microcontroller. I powered the micro from the VLDO pin, which started rising immediately after I applied power, but at 0,8V the rising voltage slope stopped, and the output remained at that voltage... Too bad, again I can't get 'through' that point. But at least I've verified that design path! If an LT / EnergyMicro engineer would give some opinion on who is causing this threshold (converter or micro): I'm all ears!
One working (with FET), one not (VLDO stopping at 0.8V)
What's next?
As you can see in the pictures I've already tested the device with the 'harvesting pan', and it works like a charm! I'll make a video, and show it here in the course of the week.
Happy harvesting!
