I’ve just seen my dyslexic moment - the pins aren’t left & right sided! Will look again after I’ve recharged my batteries!
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I suspect this battery measurement circuit is a potential cause of some of the reports of higher than expected sleep currents with Heltec dev boards.
A fully charged LiPo cell may create a high enough VGS to turn on the Mosfet and cause a 210 uA current to flow. The Mosfet will switch off when VBAT is sufficiently below VDD + VGS(th).
I am glad to hear that it is not so simple. Yesterday I did some research and found out that otherwise all circuits, to turn off the ADC voltage devider, consist of an N-channel and a P-channel mosfet. After seeing this circuit I thought Heltec might have done something clever here to save components. I had also sometimes measured 11ua deep sleep instead of my typical 3.2ua. I did not pay attention to the battery voltage. Perhaps it could also be caused by this.
What CubeCell board exactly is this about?
Where did you get the partial schematic diagram from? Is a fully complete diagram available?
Which boards exactly are you refering to here?
This is the Schematic for HTCC-AB01. The one for HTCC-AB02 looks almost identical. Only the resistance values of R16 and R17 have been changed from 10k to 100k ohms.
But what board were you talking about then, the HTCC-AB01?
I did some measurements on my HTCC-AB01 almost 2 years ago and did not notice a higher than documented/expected deep sleep current of the board. I don’t remember the battery voltage of the LiPo used but for measurements I usually use fully charged batteries.
Often both are used to allow for the switching logic to be ‘normal’ where with just a P-channel mosfet the switching logic is inverted. (0 for on, 1 for off).
The advertised 3.5uA I was only able to measure when powering directly with 3.3V (not via battery connector).
When powering with Li-ion or LiPo cell via battery connector, the quiescent current of the voltage regulator will come into play and will (also) increase deep sleep current.
Okay you are totaly right. I get 11uA at the Battery pin with 3.3v. and 3.5uA at 3.3V pin. Will charge up a battery to 4,2V and try again.
Edit: Charged up a battery to 4,2V. Got around 13uA. So it doesn’t really seem to make a difference.
Having spotted the numbers/letters on the pins weren’t what I was seeing in my head, here’s a small simulation that actually confirms the original assumption, the LiPo will slowly discharge through the ADC divider until it reaches the difference between the 3.3 and the exact value that that half of the AO7801 is at (ie real world Vgs between -0.5 to -0.9V)
You can see the step at 3.9V, at 4.1V the drain is 19uA
The thinking behind this will be that LiPo’s tend to settle quite quickly to ~3.7V so it’s not losing too much energy, but still a bit of a waste.
I personally use BSS84’s after a disappointing incident with KiCAD. They have a Vgs of -1.6V so I’ve not really thought about the potential (pun intended) for loss of potential.
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Interesting.
BSS84 is not identical to AO7801 and has different characteristics.
NXP BSS84 datasheet lists gate-source threshold voltage of Min -0.8V and Max -2V.
With VDD = 3.3V I would expect the kink in the graph to occur at 4.1V or higher instead of 3.9V. Based on the datasheet, for AO7801 I would expect it at 3.8V or higher.
Losing the will to live here - the schematic and my words say BSS84 but the graphs are set for the AO7801 with a Vgs of 0.6 - last I checked 3.3 + 0.6 = 3.9 but I’m beginning to doubt myself.
I’ve replaced the schematic.
Feel free to follow the CircuitLab link and try things out.
Hi
Does any one have an example of how to send AT commands when using the Ardunio mode. I see lots of things Around AT Enable / Disable but still no method to actually send a command. I just want to disable the Copyright message so I can use the UART.
Thanks
For this reason, I will use LiFePO4 with this solar loader for my AB01 based PM sensor. This ensures low voltage protection.
Hi @Fabltd ,
the command you are looking for is AT+Copyright=0 check out the docs https://resource.heltec.cn/download/CubeCell/AT_Command_list/CubeCell_Series_AT_Command_User_Manual_V0.6.pdf
Jay
and use this AT Command sketch demo:
I’ve been using CubeCell boards for about two years now (around 20 boards) and really recommend them.
One thing I’ve noticed is that they seem to dislike moisure. Of course, no electronic device does 
But I had several AB02A stop working (outdoor). When opening the case there was a small amount of condensation inside the case. After drying the units started to work again. I don’t blame the boards for it, but maybe this hint is useful for someone facing the same situation. I highly recommend to use pressure compensation units on the case.
I have used solar power on AB02 for almost a year, and this works well for me. I am using a 18650 li ion cell with a small 1 W solar panel (full exposure to sunlight for at least 4 hours year-round). Of course, this is no scientific analysis, but below there is some data from this setup (sending payload every 15 min SF7). After installing the node outdoors, the Li ion gets charged up and then pretty much stays at full charge for the rest of the time. Some heavy snowfalls covered the panel (and the sensor), thats where the voltage drops a little.
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Hello all,
i can confirm both findings…
one i have a cube cell connected to a lithium battery that is rated at 3000mah and produced 2500mah during test with a cut off voltage at 3.5v to protect the battery. currently the cubecell HTCC-AB01 is connected to this battery and sending a 38 byte payload every single minute, and so far it has sent 20,000.00 frames and the battery voltage is still at 4.1v, so it is promising, the board will continue to run until the voltage of the battery hits 3.5v, once there i will report my findings.
for the humidity issue, i actually suspect heat and humidity can cause some real issues for these boards as i have observed the same exact thing mentioned above. in one case the board stopped working and actually depleted the battery completely. so yes one had to take care in placing them in a sealed case (IP68) i would assume.
at what SF? air time approx doubles for each step and hence has huge impact with high throughput messaging wrt battery life… remember also FUP!
A battery that has a nominal voltage of 3.2V???
Not only mathematically unlikely as the LiPo curve dives under 4V very quickly, but promising you a visit to the court to pay the fine for the over use of the airwaves. As well as being in breach of the FUP as above.
68? Dust proof and submergible for up to 30 minutes - where will the heat go? LiPo on thermal runaway experience for the win!
Heat can only be dissipated via convection or force cooling - so the case needs holes. Humidity is take care of with appropriate sealants on the PCB. If the LiPo suffers from humidity problems, that means the Lithium is exposed to air which usually means a thin trail of smoke leading to, er, thermal runaway. So don’t buy LiPo’s that aren’t sealed and keep them in the suggested temperature range of 0℃ to 40℃ with outside limits of -20℃ to 60℃. Putting electronics in a sealed box will almost certainly stay warm - we know this from High Altitude Ballooning - if we’ve over-sealed the box it stays +10℃ whilst it is -45℃ on the outside.