Hi everyone,
I’m seeking guidance. I have a tricky situation which I don’t really know how to get out of.
I want to design a system which would consume the least amount of power possible.
The idea is to have an ESP8266 do a simple task every minute (updating a e-paper display) and sleep the rest of the time (about 5s of activity and 55s of sleep). As I want the cycles to be consistent it would be timed with a DS3231 RTC breakout board (which has it's own battery). In fact it would not sleep, it would cut its own power. The idea is derived from this post from pucebaboon.
“The idea [is] to set up an alarm on the DS3231 which will take the (DS3231) interrupt pin low when triggered. That pin is connected to the gate of a P-channel MOSFET, which functions as a power switch for the battery supply to the ESP8266. Once powered, the ESP [do its thing] and then programs a new alarm into the DS3231, clearing the interrupt and thus turning its own power off. This actually works very well. “
But it gets tricky because I want to use the potential energy of a weight to power the system. I’m going to use a stepper motor with a weight attached to its shaft as a generator. (see my previous thread about that subject)
As I understood from this previous thread the amount of energy is extremely low, so my system has to be a super low consumption (which is duable, see the second part of this video, the consumption is super low). Just to put the context, I want it to be a grandfather clock. Mixing electrical technology (epaper) with century-old way of storing energy. For the moment it is just a concept, so a 12h autonomy would be plenty. Even 4h I would take.
Stepper motor have an interesting feature that I don’t really understand, if you short the two wires of the same coil the resistance of the shaft gets really high, I think it would be enough to maintain the weight hanging.
So my idea would be to do the same as pucebaboon but to have a N-channel MOSFET shorting the wires at the output of the stepper motor. Inbetwen would be a full bridge rectifier to turn the AC current DC. As it’s shorten, it would maintain the weight hanging. As soon as the alarm of the DS3231 triggers the gate of the fet open, the resistance drop, the weight is dropping, turning the motor and the current is now powering the ESP.
(I simplified the idea, haven't put any cap)
My question is : I know it’s not going to work, but why?
When I tried to short the wire after the full bridge rectifier the resistance of the shaft is the same (why?). I can’t do it before, as mosfet are only for DC current. Or maybe a low low current relay but again it would only be powerd by the internal battery of the DS3231, which I have absolutely no clues if it exist (does it?). A mechanical solution would mean energy consumption, which I can’t afford.
It is a tricky situation. But I’m sure there is a way around.
What do you think?
I’m seeking guidance. I have a tricky situation which I don’t really know how to get out of.
I want to design a system which would consume the least amount of power possible.
The idea is to have an ESP8266 do a simple task every minute (updating a e-paper display) and sleep the rest of the time (about 5s of activity and 55s of sleep). As I want the cycles to be consistent it would be timed with a DS3231 RTC breakout board (which has it's own battery). In fact it would not sleep, it would cut its own power. The idea is derived from this post from pucebaboon.
“The idea [is] to set up an alarm on the DS3231 which will take the (DS3231) interrupt pin low when triggered. That pin is connected to the gate of a P-channel MOSFET, which functions as a power switch for the battery supply to the ESP8266. Once powered, the ESP [do its thing] and then programs a new alarm into the DS3231, clearing the interrupt and thus turning its own power off. This actually works very well. “
But it gets tricky because I want to use the potential energy of a weight to power the system. I’m going to use a stepper motor with a weight attached to its shaft as a generator. (see my previous thread about that subject)
As I understood from this previous thread the amount of energy is extremely low, so my system has to be a super low consumption (which is duable, see the second part of this video, the consumption is super low). Just to put the context, I want it to be a grandfather clock. Mixing electrical technology (epaper) with century-old way of storing energy. For the moment it is just a concept, so a 12h autonomy would be plenty. Even 4h I would take.
Stepper motor have an interesting feature that I don’t really understand, if you short the two wires of the same coil the resistance of the shaft gets really high, I think it would be enough to maintain the weight hanging.
So my idea would be to do the same as pucebaboon but to have a N-channel MOSFET shorting the wires at the output of the stepper motor. Inbetwen would be a full bridge rectifier to turn the AC current DC. As it’s shorten, it would maintain the weight hanging. As soon as the alarm of the DS3231 triggers the gate of the fet open, the resistance drop, the weight is dropping, turning the motor and the current is now powering the ESP.
(I simplified the idea, haven't put any cap)
My question is : I know it’s not going to work, but why?
When I tried to short the wire after the full bridge rectifier the resistance of the shaft is the same (why?). I can’t do it before, as mosfet are only for DC current. Or maybe a low low current relay but again it would only be powerd by the internal battery of the DS3231, which I have absolutely no clues if it exist (does it?). A mechanical solution would mean energy consumption, which I can’t afford.
It is a tricky situation. But I’m sure there is a way around.
What do you think?