ESPCLOCK4 - Dealing with low or removed batteries

One of the requirement of the ESPCLOCK project is to deal with persisting the clock time when the supply batteries run low, or when they are removed for battery change. For previous iterations of the project, a 0.47F supercap was attached to the ATtiny85 to keep it powered it long enough during a cut-off to write the clock time to flash memory.

For the ESP32, I found out it is impossible to power the main processor with the supercap, even if WiFi is not activated. It is just too power hungry! However, it is able to keep the ULP powered for 5 to 6 minutes. I found this out by getting the ULP to toggle an output pin and monitoring the output with a logic analyzer. The 0.47F supercap is placed across the 3.3V and GND pins. Power is supplied via the 5V pin. When the supply is pulled, the ULP continues to produce output for a further 5 to 6 minutes.

So the strategy I will adopt is this. The ULP will measure the supply voltage via a voltage divider.

When the supply voltage drops below a certain threshold (eg. 4.2V for 4xAA), it will stop everything. The residual power in the batteries will keep the ULP and values stored in RTC slow memory running for a very long time, until the batteries are replaced.

When the batteries are taken out for replacement, the supercap will keep the ULP and RTC slow memory intact for 5 to 6 minutes. This should give more than sufficient time for a battery change. Of course, if for whatever reason the batteries are absent for longer than this interval, the unit will have to be reconfigured by doing a factory reset.

ESPCLOCK1 / ESPCLOCK2 / ESPCLOCK3 / ESPCLOCK4

Comments

Update: Line adapter for Ozito Blade Trimmer

Update (Dec 2021): If you access to a 3D printer, I would now recommend this solution , which makes it super easy to replace the trimmer line. I have been using it for a few months now with zero issue.

3D Printer Filament Joiner

I have been looking at various ways of joining 3D printing filaments. One method involves running one end of a filament through a short PTFE tubing, melting it with a lighter or candle, retracting it back into the tubing and immediately plunging the filament to be fused into the tubing: One problem with this method is that you can't really control the temperature at which you melt the filament, so you frequently end up with a brittle joint that breaks upon the slightest bend. Aliexpress even sells a contraption that works along the same line. As it uses a lighter or candle as well, it suffers from the same weakness. I am not even sure why you need a special contraption when a short PTFE tubing will work just as well. Another method involves using shrink tubing/aluminium foil, and a heat gun: But a heat gun is rather expensive, so I wanted to explore other alternatives. The candle + PTFE tubing method actually works quite well when you happen to melt it at the rig...

Line adapter for Ozito Blade Trimmer

This is an adapter for Ozito 18V battery trimmer (and possibly some Bosch trimmers as well) that uses a plastic blade for cutting. It lets you insert a 2.4mm trimmer line (about 8cm long) and use that for cutting. Simply cut a length of trimmer line and briefly heat up one end with a lighter so that a little bulb is formed. Then insert the trimmer line into the adapter and slot that into the trimmer as per normal. Make sure the trimmer line is not so long that it touches the safety guard. If that is the case, simply trim off any excess with a cutter or scissors. This part is best printed using PETG, which is a tougher and more flexible material. PLA is more rigid and breaks more easily. However, even with PETG, it will still break when it hits something really hard. Since this takes only 0.5m of material and 15 minutes to print, I will usually print a batch of nine at a time at very little cost. The blades that they sell do not break when it hits a hard object, but ...

Random Sequence

Search This Blog