For the record: I measured the current used when in deep sleep at different supply voltage.
This is an esp-07, which still has the power LED.
I should mention that I found the esp goes mad when the supply voltage goes low (as in 3.1v) and needs a good spark (3.4V or even above) to come back to life. This is when it is active, not in deep sleep.
[later] @Harvs As said at the top, the esp-07 has an active LED. I now added the esp-12 which does not have a LED.
The ds18b20 does not make a significant difference.
I am now trying to use 4xAA (at about 5.4V initially) through an AMS1117 on the esp-12. I measured almost 3mA from the battery to the 1117 when there was no load (the LED was removed from the 1117 board, it was more like 7mA with it through a 1K resistor).
If this is a reflection of what one can expect from using a regulator then it is not promising, I hope a proper LDO does a significantly better job to make it an overall win.
Here is an example of a run with 3xAA (2300mAh NiMH) batteries without any regulation:
The voltage started at about 4.1V* and dropped below 4v after two days. After it hit 3.7v it started a nosedive and would have been depleted in less than a day.
If we supply regulated 3.3v then on the esp we save between 650uA and 80uA. How much will the LDO dissipate? How will this change if we use 4xAA(5.4-4.8v) rather than 3xAA(4.1-3.6v)?
I am ready to test this.
(*) Vdd is measured with a 12 bit ADC so the often max 4.094v read is an indication of an overflow. But I do not expect it gets much higher - I see just under 4.3v from 3xAA fresh out the charger with no load.
The 1117 is an old regulator, originally designed by National Semiconductor if I’m not mistaken, long before they were bought out by TI. Why they are popular, is because of their age they’re now a jelly bean part made by many manufacturers and are hence cheap and readily available.
Having said that, an 8051 is cheap and readily available yet we don’t bother using them anymore.
Interestingly, I was just now looking at some data sheets…
The 1117 is really bad, true.
The LM2936 seems to require higher input voltage and Iq is specified for input over 8V.
The TLV733 looks OK, with the output current on the low side but may be able to handle the short spikes of double that.
The 1825 is OK but with a higher Iq.
AMS1117 TI-TLV73333 TI-LM2936 MCP1825S
Input Voltage min (V) 4.8 1.4 5.5 2.1
Dropout Voltage (mV) 1100 1300 125 220 120 250 210 350
Quiescent Current (uA) 5000 11000 34 15 20 120 220
Output Current (mA) 1000 300 250 500
So the dropout figure you’ve got in the table above is always quoted for the max current. Typically it’s a pretty linear line because the P-channel MOSFET in an LDO exhibits pretty close to a straight resistance when saturated.
What you say is that for the bulk of the time, at around 30uA output current, the dropout is much smaller. Unfortunately the esp is most sensitive to voltage when it is active so we should always use that figure (the max). A chip that works 99.9% of the time is not good enough :-)
Can a large cap allow for better performance, meaning deliver the desired output voltage when the input is below what the above plot nominates as ‘required’ during very short peaks?
I prefer to plan for 3.3v as I found the esp is very finicky. At least my esp-07 is, I plan to test others when I have an opportunity.
How will the situation change if the supply voltage is between 4V and 5.5V (as 4xAA deliver)?
OK, so I have (too) many questions, I know, but I want to understand this and not just follow (well informed) advice.
I’m rethinking the idea of a second processor (e.g. MSP430) and just using the ESP to do the comms heavy lifting.
In that case, what I would call the “main” processor would do all time, collect the samples from the sensors and only fire up the ESP when it had some info to tx. In that case, a LDO with enable pin could be used to switch on the ESP, the advantage being there would be close to zero quiescent current through the ESP LDO.
Power for the main processor would have to be considered separately. However, power requirements are much lower, so it might be able to hang off the mid point of the AA battery stack.
Interesting. I intended to have a minimal system, and two processors surely was not my mind. The fact that the esp could do everything was attractive to me. However, using an msp as the main and “only” processor, with the esp being just a network bridge “device” is worth considering.
@Harvs What are the capabilities (storage, program store, ram, nvram) of the msp that you are considering? I expect that in terms of gpio, small buses (ow, i2c, spi…) it is well supplied. The esp could take some of this load of course, if it plays the ow/i2c/etc. bridge role casually.LAUNCHPAD
From the practical side, do we have such a processor that can be experimented with? Maybe a data sheet?
When asked for “msp430” element14 found “Microcontrollers (MCU) - 16 Bit (685)” :-(
[later] Rummaging through my stuff I found some thumb size eZ430-F2013 which may be a suitable experimenting device. The main processor has 14 pins exposed. Possible? http://www.ti.com/tool/ez430-f2013
I will note though that I paid a small fraction of what they are currently selling them for on element14. I don’t know what the story is, but the first link is 5 times the price it was in Feb. I paid $0.71ea and $0.98ea for them respectively, and they weren’t on sale. I’ve got 10 of each though, so that’s plenty to play with to prove the concept.
I also got a couple of hundred watch crystals which are suitable for use with these.
It’s good you’ve got that USB thing, that’ll serve well as a programmer. I have a launchpad which will serve the same purpose.
This does bring the question of how the two sections of circuitry will be powered. The ESP is pretty straightforward, a LDO with enable pin is pretty much it. The low power section though, there’s a couple of options. A section ultra-low power LDO is an option. Linked below are a couple of cheap devices that would probably fit the bill from element14
I’m quite keen investigating this for use with remote sensing. I have a number of friends with small farms that could do with a cheap form of remote sensing on various things.
So I’m beginning to experiment with different DIY antenna’s as well. Need to reliably get a couple of hundred meters at least to be useful.
Wow, these MSPs have very little ram. I expect they should be programmed directly with no (or minimal) system support.
The DIL package will be nice in a breadboard, but the LDOs will need to be set on a proper board.
“that USB thing” was given away for free by TI and I think that we have a few (from that time) on the shelf in the space, grab one.
So I understand that you are considering two separate LDOs for the two sections, the head unit will stay on and the esp will be turned off when not needed. This is acceptable, we can even turn off any other devices on that second supply (sensors, flash etc.).
Not sure what antennas you have in mind (high gain? directional) but I have the basic ones with the fiddly plug. One is a wire (comes with the esp-201, fits on the esp-07) the other a proper antenna from AX ( http://www.aliexpress.com/item/-/32221230205.html ).
Bugger this. I am used to people telling me I talk too much but heck, when the forum software suggests I let other people participate because over half the posts are from me … then skynet became self aware :-)
These are the smallest and cheapest MSP430’s money can buy. They have a wide range up to some quite large devices. I bought them because I only intended to use them as a real time clock and reading the temp sensor which will easily fit in. For bigger applications then a larger device of some sort would be needed.
Yes my initial thought was to use an “always on” LDO for the low power section. That LDO I linked consumes 4uA, which is probably fine. It is however 4x as much as the MSP430 will be using, so there are other options. Say charging a cap off the large LDO when it’s turned on. Just a 470uF cap would run the MSP430 in sleep mode for ten minutes. I’m open to any suggestions.
As for antennas, I’d thinking some sort of directional, medium to high gain antenna. I’d like to try making some thought, plenty of plans on the net for building a biquad which apparently gives about 11dbi gain.
If anyone opens the space this weekend I’d be happy to come in and toy around with some ideas.
As I plan to have a few of these around the house (and unknown uses in the future), I am interested in the physical form of this setup and how easy it will be to reuse it.
