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Potential Problem Reading VCC on NodeMCU

AffordableTech last edited by

Hi All,
On a NodeMCU Ver1, I was having problems with analogRead(A0) returning 65535 no matter what voltage I applied to the ADC pin?

In researching the cause, I discovered that having MY_DEBUG and/or MY_SPECIAL_DEBUG defined causes the ADC_MODE to be configured by MySensors to read the CPU VCC and thus AnalogRead(A0) returns 65535 as a 'reminder' that the ADC port is not available, Fair enough....

However, in my reading I noted that for the ESP8266 to read VCC correctly, the ADC pin must remain unconnected (floating). Here is where I see a potential MySensors problem, all the latest NodeMCU Ver 1 boards that I have been receiving have a resistor divider, making the ADC input range 0 to 3.3 Volts, therefore the MySensors VCC reading will not be reliable on these boards and there is no config setting etc that can resolve this.

I've made this post to draw attention to this as I've not seen it addressed anywhere before (despite a full day's researching the issue (see references below).

Perhaps one of the ArduinoESP8266 core developers can shed more light on this.

Regards,

Paul

Background Reading:

Bug Issues: #338 #575 #695 #696 #2672 #3168 #4009

https://forum.mysensors.org/topic/5547/wemos-d1-mini-esp8266-mysensors-and-analog-a0/6
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@donnib - I didn't continue this way but instead started using node-js based controller code that connects to a standard Ethernet gateway. @hek merged the code about two weeks ago. I will provide a tutorial on how to set it up from scratch shortly...
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First let me say that the test "network" consists of a single node and a Serial GW with a Domoticz controller only. No repeater nodes are present and it operates at 250Kbd on a frequency outside of the WiFi spectrum verified to have no traffic. The test subjects are within 10 feet of each other and the protocol sniffer receiver is placed roughly midway between the two communicating nodes. The test node has a plugable connector for the RF modules so that I can switch them out separately. The GW has the LNA/PA module and the node is using the standard mudules. Both GW and node are set to "High" power. Looking at the problem with the promiscuous protocol sniffer and wireshark I can clearly see that packets collide mid air when both the node and the GW transmitting at the same time. This happens when the controller/GW talks to the node while having the protocol ACK request enabled and the node does not have the extra wait/delay programmed. Going through 12 RF modules node side, I can see that about 1/3 shows the problem consistently to the extent that all 16 retransmissions are used up , 1/3 to various degrees and the rest shows no problems at all. Before you say "ohh fake chips etc." these modules all came from the same batch, so more than likely not fake and non fake, but rather some parameter that the lib assumes to tight of a margin for. When turning off the protocol level ACK via the controller/GW, the package goes out without an request for the node to send back the package, only the HW ack remains in the picture. Setup like this I can see that the third of the modules that cause the persistent collisions evoke a re-send of the package by the GW after ~2 to 2.5ms , while the group that shows no problem shows one single transmission from the GW only. Since the sniffer is not fast enough to capture the quick turn around ( spec says 130us) for the short HW ack to go out I can not get say whether the node is simply not sending it or just not sending it in quick enough. All I can say is that the GW code did not see a HW ack and therefore sends out the package a second time. Meanwhile on the node side all is well, it just might get the same package twice and since no status changed there is no harm done. However when you now turn on the protocol level ACK request in the controller ( as you should) the node has to turn around and send out the echo package which then collides with the resend of the original package from the GW. The node also doesn't get an HW-ACK becasue of this and tries to resend the echo package over again until it runs out of tries. When I then introduce the wait/delay in the code above to wait out the 2.5Ms for the GW to resend the initial package this ACK/resend storm goes away because the air is clear when the node sends it's echo package. If I wait/delay for 2 ms the problem is greatly reduced and if I wait 3 ms I see no more evidence of collisions. Either wait or delay works however, I choose delay() to be positively sure that no other communication is started during that time by the node. I conclude that as a work around this solves the issue we are having with the RF24 transport, but without further investing into faster RF sniffing equipment I can't say for sure if this could be solved better on the TX side by waiting longer for the HW ack to arrive from the receiving node, however I think there would be a good chance for that. There is also a chance that the PA/LNA module used on the GW could be part of the problem by not being able to switch quickly enough back to RX mode and therefore loose the HW-ACK for nodes that respond quicker than others. Edited: Checked with a non PA/LNA module on the GW and no change could be observed, so this theory can be discounted. BTW: All of this is very reminiscent of an email communication in 2015 I had with Ekblad !! GS
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Bug Reports • • prawnpie

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@OldSurferDude I've run into a similar issue where I was sending data from the controller to an actuator node with mutliple relays and having commands get dropped when sent in rapid succession. I agree that an extra millisecond of wake time every 4 hours will make a negligible difference on total power draw and I'm OK adding a wait now that I know that I need to do it. I agree that it might not make sense to build this support in to MySensors unless we find the optimized time with your method and then... I don't know... add a hacky/naive solution of having the RFM95W sleep implementation block before sending the sleep command,... I don't know the MySensors architecture whether that's even feasible without breaking some rules. My secondary point of posting was definitely just to add to the knowledge base in this forum so someone else trying to put a Lora radio to sleep would find this and save some time.
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@Branther Thank you for your feedback!
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@ltigges Hi, I can confirm your issue. Thank you for reporting! Best will be to open a new issue in in the GitHub repo at MySensors/issues. It would be great if you could do that- thank you. BR Immo
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@monte said in Boards esp8266 v3.1.0 or Newer Doesn't Work with MySensors: il existe tellement de solutions bon marché et faciles pour ce que font mysensors as rich in possibilities as this does not exist

Potential Problem Reading VCC on NodeMCU

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Potential Problem Reading VCC on NodeMCU

Suggested Topics

Code for beta-testing? Controllers • • andriej

ACK -aka ECHO beeing missed by Serial Gateway with RF24 radios. V2.3.2 Bug Reports • • GaryStofer

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Bug Reports • • Branther

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