Potato Powered Microcontroller

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Testing the Potato Battery
Jake Wachlin • 8 hours ago • 0 comments

After the initial tests using saltwater and salty vinegar with pennies and nickels were promising but not enough power, I moved on to testing with a sweet potato and zinc electrodes (zinc plated plate, screws, and nails). The first test is shown below. With a nickel and a zinc plate, I was able to achieve a cell open circuit voltage of 915mV, much higher than the prior cells. With a zinc plated nail, it was even higher, at 1.01V! This was very promising that I would be able to use this setup to power the Nanosleeper.
To prepare for testing, I modified the Nanosleeper firmware to sleep more and be in awake mode less. However, I still wanted it to wake reasonably often to flash its LEDs, so I can tell what's happening. Testing the Nanosleeper firmware with MetaShunt, I determined the average current was now 125uA. So, when we give it a 2.1V supply, it takes an average of 263uW to run. The boost converter takes about 55uA at 0.5V, so another 28uW, leading to a total of 291uW. It could certainly be lower with different boost converters (such as the TPS61098, which takes 300nA and can boost down to 0.7V), I'm doing this testing with what I have on hand!
OK, now I set up a series battery with two chunks of potato, 2 nickels, and 2 zinc-plated nails. I was able to use this to charge up a 3300uF capacitor up to 1.6V. I then connected the TPS61200 board, but not the Nanosleeper to the 2.1V rail. I confirmed the 2.1V rail is generated temporarily, but eventually the capacitor drains down and the system settles into the current and voltage shown below (296mV at 168uA). At this voltage, nothing works, but it does provide some insight into the IV curve. At 296mV, this battery provides 50uW, far from the 291uW needed. I probably need bigger electrodes to be able to provide more current.
Initial Tests - US Coin Batteries
Jake Wachlin • 8 hours ago • 0 comments

My first testing for this idea was to use pennies (for their outer copper layer) and nickels (which are mostly made of nickel) as the electrodes, with saltwater or salty vinegar as the electrode.
The first tests were to evaluate the open circuit voltage of such batteries. The images below show the results: with saltwater an open circuit voltage of 229mV was seen. With salty vinegar as the electrode, a higher open circuit voltage of 472mV was seen.
I then performed some testing to determine the short circuit current possible from these cells. With both saltwater and salty vinegar, the cell achieved an short circuit current of 399uA, as seen below.
These initial results were promising. I have a development board design of the TPS61200, which is a 0.3V input boost converter with 55uA quiescent current, and Nanosleeper could easily require an average of <150uA to operate significantly on. While these two measurements don't tell us the IV curve of the cell, it seemed in the ballpark to be able to run Nanosleeper from the TPS61200, especially if some capacitance is included to help with buffering power.
I assembled a battery consisting of three layers of penny/vinegar-soaked-paper-towel/nickel cells, and connected that to a 2.5F supercapacitor. This supercapacitor was initially charged without another load on it. Then, I connected the TPS61200 development board, which boosted the roughly 0.6V output from this battery up to 2.1V, which was then provided to Nanosleeper. Nanosleeper was set to be awake with LEDs on for several seconds, then on with LEDs off for several seconds, then entering deep sleep for several seconds. The average current was roughly 250uA. The video below shows the Nanosleeper waking up, powered only from energy from this battery. However, this battery cannot provide enough power to keep the system on, so more tests to come!