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This should work right?
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paulca:

--- Quote from: Twoflower on October 06, 2019, 03:36:35 pm ---ESD != Earth bonding.
--- End quote ---

Yes, sorry I meant the fact I have low voltage probes connected to copper pipes.  In the UK (and most places?) the copper pipes form part of the Earth circuit of the house.  I'm sure some grey beards will tell me this isn't worth considering, but I seen the potential that an Earth fault in the house, could see the copper piping could surge to 240V if my circuit presents a better route to Earth than the rest of the pipe it could take current.

On the ESD.  If the NodeMCU has inheritied charge from the carpet and the USB charger is floating, it is still fine is it has 10000V and 10005V input... unless I move it :)  But yes, I need cases, that's the purpose of the project. :)



--- Quote from: Twoflower on October 06, 2019, 03:36:35 pm ---I wonder a bit that the in and out-flow temps are so close together. It seems you don't take much heat from it even as the system heats up the water. But I'm no expert here.

--- End quote ---

It's interesting and only because I fitted those probes do we know this is the case.  They are definitely reading right.  It's a sign my heating system is old and tired.  The pump rate is probably to high and the radiators too old and gunked up that it's not taking as much heat as it could from the system.

If you do some sums, OUT temp - IN temp is about 2*C.  An estimate of the total water volume in the system and an assumption is circulates uniformly results in a sizable amount of kW.  I don't have the numbers on hand, but I did them.  It was well below the boiler output though, maybe 25% of it.  If I was keeping this system I'd swap out the pump for a slower flow rate.

EDIT: It also has to be considered I have an inline heat exchanger in the hot water tank, so that will act as a ballast or temperature buffer in the system.

I am having my whole heating changed from oil to gas next month, with a few radiators being replaced and the system flushed and will draw a new baseline there.
Twoflower:
I'm not sure if you understood the ESD problem. It is not directly the potential itself but the charge. You build up a charge up by walking on the carpet. Now you touch a device. Now you have en energy flow from you to/through the device. This could damage the device.

By the way. Your Espressif is probably floating about 55V above ground level if powered by a wall wart. Your wall outlet has 110V, due to capacitors in the wall-wart you will have half of it on the device. You can measure it with a multimeter.

The datasheet of the ESP says: Tested and passed up to 1.5kV on all pins (not 10kV as you write). And if you feel a zap you already reached about 2...3kV -> potential damage of the device. That page contain a table about some voltages a human body could charge up to (spoiler: walking on a carped in dry air: 35kV): https://www.esda.org/esd-overview/esd-fundamentals/part-1-an-introduction-to-esd/

I just get a bit nervous seeing electronics laying on synthetic fibers ;-) Just be careful, because debugging a ESD damaged device is a pain until you figured out you have a defective device. Often they still work partly, but one IO pin isn't working as expected, reading wrong values, reduced performance...
paulca:
So... not giving up just yet.  If it's reading off because of heat from the MCU, what if I put the MCU into deep sleep for most of the time.  While active the device is pulling around 60mA, but in deep sleep it is only pulling 300uA.  A WeMos Mini without the temp probe pulls just the same, so the sensor quiescent current is fine.

First tests with a 5 second deep sleep seemed to have a significant effect, but it stabilised about 5*C too high still.

I am testing with a 30 second sleep it's currently sitting at around 2*C high, but it's still falling slowly, so I'll reserve judgement until it stabilises.  I don't mind it being consistently out by, say, 1*C, I'm not intending on measuring absolutely temperature, just indicative and relative temperatures for heating automation.  So whether I feel I like 20*C or 21*C for a room, it doesn't really matter.

I think I will also put it side by side with a leaded probe and log both temps for a while and see how close it gets.
Twoflower:
Yes, that's also an option. The less power the system consumes the less heat will be emitted from the system. The WLAN should be on as little as possible as this consumes reasonable power. So as soon as you transmitted the data switch the WLAN off. I haven't looked into the power options of the ESP, but probably you can disable much more as reading the 1W sensor does not need much of the functionality included in the ESP.

If you do one temperature measurement every 30 seconds and leave the deep-sleep for 5 seconds during data-transfer you'll have some positive impact. And you can alternatively do multiple measurements (no WLAN enabled) and store the data in the ESP and send the data every 10 Minutes (less frequent is better). With this the impact will be much less.

An alternative might be using a much simpler controller and use zigbee (or some other low power wireless system) hat. Doing such measurements don't need much CPU power. Thus much less self heating. The down-side is that this would require a zigbee bridge in your house.
paulca:
I have the ESP8266 in deep sleep for 30 seconds.

It does this:
Wake up
Enable  1W bus and set pin modes for it.
delay 750ms to allow 1W sensor to begin conversions
read sensor
Start Wifi connect
Wait on Wifi connect
Send UDP packet
Wait 500ms
Deep sleep for 30 seconds

The sensor is still reading consistently 3*C high.  It's much better than 10-11*C high, but still... too high.

I even tried WAKE_RF_DISABLED and kept the Wifi off until I'd read the sensors, but it added more trouble than it solved as I can wake and read the sensors in under a second.

I have also tested with a 5 minute sleep and the temperature looks to be at most 1*C too high maybe less.  It's probably fine for my purposes, but the 5 minute sleep isn't unfortunately.  I need higher resolution than that.  My current sensors are set for 5 second interval which might not make a lot of sense for the heating control, but does calm my OCD about watching data displays intently.  The 5 second interval does upset Home Assistant a bit, but I find that somewhat amusing and it's not my primary "hub".

I'm going to try adding 10cm of aluminium wire for the probe lead, covered in heatshrink to look a bit better.  I expect that will fix the heat issue.  Aluminium apparently has less heat conductivity but will serve my electrical purposes fine.  (Assuming my cheap thin gauge wire is aluminium and not tinned copper).

My existing sensors do not even deep sleep and read what appears to be fine.
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