Part 4: Outdoor Temperature Logging with ESP8266 ESP-12f

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I am sure you will have realised that none of this series is a tutorial, while I am competent in some areas, with this project I am just another programmer desperately trying to learn the hardware.

I really appreciate all the input from you all, I am hopefully learning a lot. I am getting a little stuck in the mud making this thing work well, I hope I can pick up an appropriate Mosfet soon.

It is funny really, I have always just used Mosfets like a switch, I never really considered anything other that the gate threshold and current capability. Learning mode enabled.

It turns out that 'Likes' and 'Shares' actually help the channel so, if you want to, please click the thumbs up or share the video.

If you want to get in contact Twitter is probably the best way @mrdavidjwatts

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Have you considered trying a voltage regulator with a low quiescent current? The LT1763 for example is designed for battery powered circuits, and has a quiescent current of only 30uA.

StvenAU

Great design, David! A couple of errors in the "script". At 2:51 you talk about the "resistance over the gate and source". I'm sure you meant "drain and source". The resistance between gate and source is more or less infinite. It's a small capacitance however which we like to include in the impedance equations. ;-) Let's not go down that road. It's only valid for high frequencies. Thumbs up!

roberteliassen

im no engineer, but BS170 is not a logic level mosfet (a logic mosfet will typically fully saturate at 5V not 10V). you should hit that gate with atleast 8V. threshold voltage is where it just begins to conduct (usually with very small loads). you will want to ensure you fully saturate the gate to fully turn it on as a switch (look for the graphs at the bottom of the datasheet). if you dont then your Rds will be alot higher which not only drops your voltage (as you said) but increases it heat and might let out magic smoke. you might think about a bypass cap between the fet and esp as well.
TLDR; dont look at gate threshold, saturate the FETs gate!

purple mat looks cool.

lotsarats

Excellent as always, thanks. Just in case nobody has mentioned him have you seen the work Kevin Darrah does on low energy electronics? He did an arduino based video where he turned just about everything off...yet kept it active, it could be a good source of info.

mrtom

I know you said you wanted to do this in order to provide an option for people who have this and other MCU boards with regulators such as the AMS1117 and wanting to do low power stuff, but was there any particular reason you hadn't considered simply bypassing the regulator, and using a switching regulator or LDO with a better quiescent current, and just injecting it into the VCC/3v3 line? Or is that going to be a topic of a later video? :-P

pfeerick

nice work bud its good to no normal humans are doing a bit of electronics!

andymouse

Alternative use a LiFe battery about 3.3560v to about 3.0v range, skip regulator and just have the ESP8266, check data sheet if voltage range works. The esp has a RTC and more important the ram for the clock has 512 extra addresses for any use. These registers remain even if reset as long as the power is connected, but all ram is lost. Use a flag in one memory location and an a counter in another. use the deep sleep with a high number, when it wakes test the flag and a counter, is enough time elapsed then run internet, reset max count, else decrement counter and sleep again. watch Andreas Spiess,
#60 How to use the RTC Memory in ESP8266 and reduce power consumption by factor of 10 (Tutorial).

grahamwise

I'm working on a similar circuit using an ATtiny85 to switch on/off a Wemos D1 mini via an IRF540n MOSFET, logging the DS18b20 temperature to Thingspeak (30 min intervals). It all works fine but I'm having problems when the Wemos powers up as the temperature readings is fixed at 85 Deg C. A quick press of the reset fixes this (temperature reads correctly) but on the next power up the problem returns. Everything is fine when powering from the PC USB port. Very frustrating!!

peterleather