Lmic plus rfm95w staying awake for long periods


(Grazy) #31

For your delay i think you should track when LMIC really want to send data , for that you can add some printf in “engineUpdate” for the variable “txbeg”

Someting like

#endif // !DISABLE_BEACONS

        // Trace to show the delay due to duty cycle. 
        LMIC_DEBUG_PRINTF("%ul: engineUpdate, tx will happen at %ul\n", os_getTime(), txbeg);

        // Earliest possible time vs overhead to setup radio
        if( txbeg - (now + TX_RAMPUP) < 0 ) {

And if the delay is due to txbeg then you will be able to track where it come from.


(Miwo) #32

I fancy, I need to go back two steps here at least checking more basic things.
I have to admit, I never let the “same” code on the same node run for long without the sleep. Did not feel the necessity, though it seems to be better now.
I have now set up a very simplified node, sending 2 bytes every 5 minutes not getting downlinks.
First test will be with a delay(2000), 150 times between the sends. No sleep and no tinkering with the timer.

Edit:
You also asked for the SF. This is what the data says for one example:

{
  "time": "2019-01-06T17:44:41.269366308Z",
  "frequency": 868.5,
  "modulation": "LORA",
  "data_rate": "SF7BW125",
  "coding_rate": "4/5",
  "gateways": [
    {
      "gtw_id": "eui-b827ebfffe032416",
      "timestamp": 1130906507,
      "time": "",
      "channel": 2,
      "rssi": -83,
      "snr": 7.8,
      "rf_chain": 1,
      "latitude": 47.53158,
      "longitude": 7.81542,
      "altitude": 395
    }
  ]
}

And from the gateway:

{
  "gw_id": "eui-b827ebfffe032416",
  "payload": "QCQuASaAAgABmJwwYjTD",
  "f_cnt": 2,
  "lora": {
    "spreading_factor": 7,
    "bandwidth": 125,
    "air_time": 46336000
  },
  "coding_rate": "4/5",
  "timestamp": "2019-01-06T17:53:34.110Z",
  "rssi": -78,
  "snr": 9.2,
  "dev_addr": "26012E24",
  "frequency": 868300000
}

(Miwo) #33

Here I am a bit at a loss.
How do I get the LMIC_DEBUG_PRINTF to put something out to serial?
I can increase debug_level to 1 which gives me out of memory in variable space. Bad.
So I changed most of the #if LMIC_DEBUG_LEVEL > 0 to #if LMIC_DEBUG_LEVEL > 5 just to make them not print.
Now it compiles, but nothing of the PRINTFs is sent to serial. :thinking:


(Grazy) #34

To get LMIC_DEBUG_PRINTF to work, you have to uncomment

//#define LMIC_PRINTF_TO Serial

Or you can replace the LMIC_DEBUG_PRINTF with some Serial.print().

Serial.print(os_getTime());
Serial.print(F(" : engineUpdate => tx will happen at "));
Serial.println(txbeg);


(Miwo) #35

OK, got it. Thank you a lot for helping me here.
Had to change the line to that, though, so to get the actual values:

LMIC_DEBUG_PRINTF("%lu: engineUpdate, tx will happen at %lu\n", os_getTime(), txbeg);

Btw: I did some other test. If I send packets with a payload of 25 bytes as fast as I can, the LMIC soon delays it to 12 seconds between the packets. They have an airtime of about 100 ms, so that’s about 1% airtime.
Now, reverting to one send every 5 minutes without sleep, I can sit and wait what happens.


(Miwo) #36

After having run some code for 6h and 9h respectively, I have more information but nothing conclusive yet.
I changed the time output to be divided by OSTICKS_PER_SEC to get seconds which are easier to read

So, 6h of sending every 5 minutes without sleep (only 150x 2s delay) and no tinkering with the timers:
Debug looks like this from beginning to end:
go to sleep … … woke up …sending…

22345: Queue packet
22345: engineUpdate, tx at 21738; now is: 22345
22345: EV_TXSTART
22345: tx done
22351: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep … … woke up …sending…
22651: Queue packet
22651: engineUpdate, tx at 22085; now is: 22651
22651: EV_TXSTART
22651: tx done
22656: EV_TXCOMPLETE (includes waiting for RX windows)
sent

Then changed to sleep for 2 seconds instead of the delay. First 6h no difference, no inexpected delays:

go to sleep … … woke up …sending…
33976: Queue packet
33976: engineUpdate, tx at 33369; now is: 33976
33976: EV_TXSTART
33976: tx done
33982: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep … … woke up …sending…
34282: Queue packet
34282: engineUpdate, tx at 33716; now is: 34282
34282: EV_TXSTART
34282: tx done
34288: EV_TXCOMPLETE (includes waiting for RX windows)
sent

Then, after 9.52 hours, this happens:

go to sleep … … woke up …sending…
34282: Queue packet
34282: engineUpdate, tx at 33716; now is: 34282
34282: EV_TXSTART
34282: tx done
34288: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep … … woke up …sending…
-34131: Queue packet
4294933165: engineUpdate, tx at 33981; now is: 4294933165
-34131: EV_TXSTART
4294933165: tx done
-34126: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep … … woke up …sending…
-33826: Queue packet
4294933470: engineUpdate, tx at 34328; now is: 4294933470
-33826: EV_TXSTART
4294933470: tx done
-33819: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep … … woke up …sending…
-33519: Queue packet
4294933777: engineUpdate, tx at 4294933170; now is: 4294933777
-33519: EV_TXSTART
4294933777: tx done
-33513: EV_TXCOMPLETE (includes waiting for RX windows)
sent

So, rollover happend, first for now, then for txbeg. No problem so far, as still no send delays.
Next test will be sending not every 5 minutes but every 1 hour. Maybe this causes the problem to show up.


(Arjan) #37

I don’t know if rollover occurred yet; it seems the debug print is just thinking it’s a signed value, rather than an unsigned value. For an unsigned number, the value seems to have passed half its maximum then. But sure: at some point it will rollover.

Ah, forget the negative printed values, these are the lines that you’re referring to:

34282: engineUpdate, tx at 33716; now is: 34282
...
4294933165: engineUpdate, tx at 33981; now is: 4294933165
...
4294933470: engineUpdate, tx at 34328; now is: 4294933470
...
4294933777: engineUpdate, tx at 4294933170; now is: 4294933777

Are all times in each line divided by OSTICKS_PER_SEC?

Something I noticed which is a bit weird, but might not affect things, os_getTime is defined as:

ostime_t os_getTime () {
    return hal_ticks();
}

…with hal_ticks expected to return an unsigned 32 bits number:

u4_t hal_ticks () {
    ...
}

…but ostime_t being a signed 32 bits number:

typedef uint32_t           u4_t;
typedef int32_t            s4_t;
...
// the HAL needs to give us ticks, so it ought to know the right type.
typedef              s4_t  ostime_t;

(Miwo) #38

Yes, all are divided by OSTICKS_PER_SEC.
Regarding the negative numbers. Next time I stop the script, I will check if I can/have to cast some printouts as unsigned long not to look different because of them flipping over to negative.

And now, having it run with one wakeup per hour and 1800 times a 2 second sleep with same number of 2 seconds “corrections” on the timer, I can see “bad thing happening” after only a couple of hours:

Starting
 ...sending...
0: Queue packet
0: EV_JOINING
0: engineUpdate, tx at 3; now is: 0
0: next engine update in 3
3: engineUpdate, tx at 3; now is: 3
3: EV_TXSTART
3: tx done
8: EV_JOINED
8: engineUpdate, tx at 8; now is: 8
8: EV_TXSTART
8: tx done
13: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep ... ... woke up ...sending...
3612: Queue packet
3612: engineUpdate, tx at 8; now is: 3612
3612: EV_TXSTART
3612: tx done
3617: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep ... ... woke up ...sending...
2921: Queue packet
2921: engineUpdate, tx at 54; now is: 2921
2921: EV_TXSTART
2921: tx done
2928: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep ... ... woke up ...sending...
2231: Queue packet
2231: engineUpdate, tx at 2967; now is: 2231
2231: next engine update in 2967
2967: engineUpdate, tx at 2967; now is: 2967
2967: EV_TXSTART
2967: tx done
2973: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep ... ... woke up ...sending...
2277: Queue packet
2277: engineUpdate, tx at 3014; now is: 2277
2277: next engine update in 3014
3014: engineUpdate, tx at 3014; now is: 3014
3014: EV_TXSTART
3014: tx done
3019: EV_TXCOMPLETE (includes waiting for RX windows)
sent
go to sleep ... 

Time seems to be, well, running very slow or even backwards in between. And all of a sudden, tx is after now and it delays.

Again, this is the code used instead of a simple delay(2000);:

  LowPower.powerDown(SLEEP_2S, ADC_OFF, BOD_OFF);
  //Give the AVR back the 2 slept seconds
  unsigned long slept=2*1000;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    extern volatile unsigned long timer0_millis;
    extern volatile unsigned long timer0_overflow_count;
    timer0_millis += slept;
    // timer0 uses a /64 prescaler and overflows every 256 timer ticks
    timer0_overflow_count += microsecondsToClockCycles((uint32_t)slept * 1000) / (64 * 256);
  }

Strange, isnt’ it?

I tried a different approach with a different node running on a AA battery (no serial though):
If I do not try to give it back all the time it slept, but only just enough so that the duty cycle is within limits (e.g. 1 minute per send or per hour, probably 10 sec would also suffice), it seems to run nice.
I do not know if I just delay the problem doing so, or if it is now gone completely. But the node is running for >24h now without showing any problems. It might take weeks to find out, but with now no longer showing the power-hungry delays, the battery should last about a year now on that node, according to my estimates :wink:
I know this is just a nasty patch, but unless somebody has a good idea what causes these time-effects, I am lost in getting it fixed properly.


(Arjan) #39

As an aside: at least for EU868, it seems the value for tx at 8 is taken from the earliest time any of the channels is available, which indeed can be in the past. So that looks okay.


(Amedee) #40

Some theory…

os_time is based on millis, it is a scaled down version of millis to avoid to overflow too often.
To keep the os_time counter accurate, it needs to detect millis overflow, which happens after approx 71 minutes.
The detection algorithm looks at a flip of the most significant bit of millis.

Now if you sleep one hour, most of the time (1 out of 6) you will have a millis overflow, and it won’t be detected as the increment is big enough to keep the msb unchanged!
And if you are out of luck, it will go backwards…

This is not a proven theory, it is just my gut feeling reading the code, but you could validate it easily by calling os_getTime() each time you wake up (every 2 secs) to allows overflow detection.


Dragino LoRa shield with LMIC and 1-Wire sensor problem
(Arjan) #41

Nice find! And that also explains why the correction code might work just fine when waking up from code, rather than from an external interrupt, as then the maximum sleep time is so much smaller? (Often people need a loop to sleep repeatedly to achieve longer times.)


(Amedee) #42

I guess if you really sleep (that is: delay()), you would get the same behaviour as the IBM co-routine mechanism does not benefit from yield()
The thing is in non-hardware sleep, you would just re-schedule a task, not slepping.

But we see that in the 5 min test the clocks are behaving better because we call os_getTime() more often.

As the overflow if about 71 minutes, we need to ensure we update at least twice in that timeframe, so if we update every 30 mins, we shoudl be good…

(again: to be tested…)


(Miwo) #43

The code you quoted is essentially the basis for my code and it works as long as the total sleep time between sends does not exceed a certain limit. This limit is based on the explanations from @Amedee in the previous post. I will summarise my findings in a separate post now.


(Miwo) #44

Ok, after doing more testing I think I got a pretty good and complete picture of what happens and how to avoid it.
Actually @Amedee hit the point brilliantly well by analysing the os_time counter and the os_getTime() function.

Sleeping the AVR works well if os_time is kept accurate, which can be achieved by calling os_getTime() regularly. As he explained, regularly means at least about every 30 minutes. More often is better.
Contrary to what I thought, calling os_runloop_once() does not update os_time whereas doing an actual send does. Hacking the times is also only neccesary if the tasks between the sleep does not exceed the time required for the duty cycle anyway (rarely, I guess).
The full procedure with updating time0_overflow_count and timer0_millis in atomic mode is not needed. The simple timer0_overflow_count hack with disabled interrupts (cli, sei) is sufficient but will make your millis() lag behind. Should not matter except for special cases.
If you put the AVR to sleep forever and wake it by interrupt, do not modify the time by more than 30 minutes afterwards regardless how long the sleep was. Better only add e.g. 1 minute which is sufficient for the duty cycle, do the os_getTime() and you are good. Adding e.g. 60 minutes at once will give you problems from time to time.

In short:
You can put the AVR to sleep as short or as long as you like.
You should add only limited time (minutes!) to timer0_overflow_count after sleep.
Always call os_getTime() after modifying timer0_overflow_count to get the os_time updated.
You do NOT need to call os_runloop_once() after waking as it does “not do anything helpful” at that time.

Many thanks to all of you helping find these nasty send delays and get this sorted out. This really is a forum with brilliant, knowledgeable and helpful people being around! :man_student:

Finally, here is a working example code sending every hour and sleeping in between:

/*******************************************************************************
 * Copyright (c) 2015 Thomas Telkamp and Matthijs Kooijman
 * Copyright (c) 2018 Terry Moore, MCCI
 *
 * Permission is hereby granted, free of charge, to anyone
 * obtaining a copy of this document and accompanying files,
 * to do whatever they want with them without any restriction,
 * including, but not limited to, copying, modification and redistribution.
 * NO WARRANTY OF ANY KIND IS PROVIDED.
 *
 * This example sends a valid LoRaWAN packet with payload "Hello,
 * world!", using frequency and encryption settings matching those of
 * the The Things Network.
 *
 * This uses OTAA (Over-the-air activation), where where a DevEUI and
 * application key is configured, which are used in an over-the-air
 * activation procedure where a DevAddr and session keys are
 * assigned/generated for use with all further communication.
 *
 * Note: LoRaWAN per sub-band duty-cycle limitation is enforced (1% in
 * g1, 0.1% in g2), but not the TTN fair usage policy (which is probably
 * violated by this sketch when left running for longer)!

 * To use this sketch, first register your application and device with
 * the things network, to set or generate an AppEUI, DevEUI and AppKey.
 * Multiple devices can use the same AppEUI, but each device has its own
 * DevEUI and AppKey.
 *
 * Do not forget to define the radio type correctly in
 * arduino-lmic/project_config/lmic_project_config.h or from your BOARDS.txt.
 *
 *******************************************************************************/

#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>
#include <LoraMessage.h>

#include "LowPower.h"
//#include <util/atomic.h> //Only needed for full version to update time

volatile boolean powerdown=false;

unsigned int Vbat;

// This EUI must be in little-endian format, so least-significant-byte
// first. When copying an EUI from ttnctl output, this means to reverse
// the bytes. For TTN issued EUIs the last bytes should be 0xD5, 0xB3,
// 0x70.
static const u1_t PROGMEM APPEUI[8] = { XXXX };
void os_getArtEui (u1_t* buf) {
  memcpy_P(buf, APPEUI, 8);
}

// This should also be in little endian format, see above.
static const u1_t PROGMEM DEVEUI[8] = { XXXX };
void os_getDevEui (u1_t* buf) {
  memcpy_P(buf, DEVEUI, 8);
}

// This key should be in big endian format (or, since it is not really a
// number but a block of memory, endianness does not really apply). In
// practice, a key taken from ttnctl can be copied as-is.
// The key shown here is the semtech default key.
static const u1_t PROGMEM APPKEY[16] = { XXXX };
void os_getDevKey (u1_t* buf) {
  memcpy_P(buf, APPKEY, 16);
}

static osjob_t sendjob;

#define TX_INTERVAL 3600           //seconds of sleep between sends
#define SLEEPCYLCES TX_INTERVAL/8  // calculate the number of sleepcycles (2s/8s) needed for the given TX_INTERVAL

// Pin mapping
const lmic_pinmap lmic_pins = {
  .nss = 10,
  .rxtx = LMIC_UNUSED_PIN,
  .rst = 4,
  .dio = {2, 3, LMIC_UNUSED_PIN},
};


void onEvent (ev_t ev) {
    Serial.print((unsigned long)(os_getTime()/ OSTICKS_PER_SEC));
    Serial.print(": ");
    switch(ev) {
        case EV_SCAN_TIMEOUT:
            Serial.println(F("EV_SCAN_TIMEOUT"));
            break;
        case EV_BEACON_FOUND:
            Serial.println(F("EV_BEACON_FOUND"));
            break;
        case EV_BEACON_MISSED:
            Serial.println(F("EV_BEACON_MISSED"));
            break;
        case EV_BEACON_TRACKED:
            Serial.println(F("EV_BEACON_TRACKED"));
            break;
        case EV_JOINING:
            Serial.println(F("EV_JOINING"));
            break;
        case EV_JOINED:
            Serial.println(F("EV_JOINED"));
            /*
            {
              u4_t netid = 0;
              devaddr_t devaddr = 0;
              u1_t nwkKey[16];
              u1_t artKey[16];
              LMIC_getSessionKeys(&netid, &devaddr, nwkKey, artKey);
              Serial.print("netid: ");
              Serial.println(netid, DEC);
              Serial.print("devaddr: ");
              Serial.println(devaddr, HEX);
              Serial.print("artKey: ");
              for (int i=0; i<sizeof(artKey); ++i) {
                Serial.print(artKey[i], HEX);
              }
              Serial.println("");
              Serial.print("nwkKey: ");
              for (int i=0; i<sizeof(nwkKey); ++i) {
                Serial.print(nwkKey[i], HEX);
              }
              Serial.println("");
            }
            */
            // Disable link check validation (automatically enabled
            // during join, but because slow data rates change max TX
            // size, we don't use it in this example.
            LMIC_setLinkCheckMode(0);
            break;
        /*
        || This event is defined but not used in the code. No
        || point in wasting codespace on it.
        ||
        || case EV_RFU1:
        ||     Serial.println(F("EV_RFU1"));
        ||     break;
        */
        case EV_JOIN_FAILED:
            Serial.println(F("EV_JOIN_FAILED"));
            break;
        case EV_REJOIN_FAILED:
            Serial.println(F("EV_REJOIN_FAILED"));
            break;

    case EV_TXCOMPLETE:
      
        Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));

        if (LMIC.txrxFlags & TXRX_ACK)
        Serial.println(F("Received ack"));

        Serial.println(F("sent"));

      //send/receive cycle completed
      powerdown=true;
      break;
    
        case EV_LOST_TSYNC:
            Serial.println(F("EV_LOST_TSYNC"));
            break;
        case EV_RESET:
            Serial.println(F("EV_RESET"));
            break;
        case EV_RXCOMPLETE:
            // data received in ping slot
            Serial.println(F("EV_RXCOMPLETE"));
            break;
        case EV_LINK_DEAD:
            Serial.println(F("EV_LINK_DEAD"));
            break;
        case EV_LINK_ALIVE:
            Serial.println(F("EV_LINK_ALIVE"));
            break;
        /*
        || This event is defined but not used in the code. No
        || point in wasting codespace on it.
        ||
        || case EV_SCAN_FOUND:
        ||    Serial.println(F("EV_SCAN_FOUND"));
        ||    break;
        */
        case EV_TXSTART:
            Serial.println(F("EV_TXSTART"));
            break;
        default:
            Serial.print(F("Unknown event: "));
            Serial.println((unsigned) ev);
            break;
    }
}

void do_send(osjob_t* j) {
  
  // Check if there is not a current TX/RX job running
  if (LMIC.opmode & OP_TXRXPEND) {
    Serial.println(F("OP_TXRXPEND, not sending"));
  } else {

    //Prepare data
    LoraMessage message;

    message.addUint16(Vbat);
    
    // Prepare upstream data transmission at the next possible time.
  
    Serial.print((unsigned long)(os_getTime()/ OSTICKS_PER_SEC));
    Serial.print(": ");
    Serial.println(F("Queue packet"));
    
    LMIC_setTxData2(1, message.getBytes(), message.getLength(), 0);    

  }
  // Next TX is scheduled after TX_COMPLETE event.
}



void setup() {

  Serial.begin(115200);
  Serial.println(F("Starting"));

  // LMIC init
  os_init();

  // Reset the MAC state. Session and pending data transfers will be discarded.
  LMIC_reset();
  LMIC_setClockError(MAX_CLOCK_ERROR * 1 / 100);  //Relax RX timing window

  // Start job (sending automatically starts OTAA too)
  measure();  //Do a first measurement at startup
  powerdown=false;
  os_setTimedCallback(&sendjob, os_getTime() + ms2osticks(10), do_send);
}

void loop() {

  extern volatile unsigned long timer0_overflow_count;
  os_runloop_once();  //check send status

  if (powerdown) {

    Serial.println(F("go to sleep ... "));
    Serial.flush();
    
    for (int i=0; i<SLEEPCYLCES; i++) {
      // Enter power down state for 8 s with ADC and BOD module disabled 
      LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
      //LowPower.powerDown(SLEEP_2S, ADC_OFF, BOD_OFF);
            
      //Give the AVR back the slept time back (simple version)
      cli();
      timer0_overflow_count += 8 * 64 * clockCyclesPerMicrosecond(); //give back 60 seconds of sleep
      sei();

      /*      
      //Give the AVR back the sleep time; full version with millis() update
      //Needs '#include <util/atomic.h>'
      unsigned long slept=8*1000;
      ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
        extern volatile unsigned long timer0_millis;
        extern volatile unsigned long timer0_overflow_count;
        timer0_millis += slept;
        // timer0 uses a /64 prescaler and overflows every 256 timer ticks
        timer0_overflow_count += microsecondsToClockCycles((uint32_t)slept * 1000) / (64 * 256);
      }
      */     
      
      os_getTime();   //VERY IMPORTANT after sleep to update os_time and not cause txbeg and os_time out of sync which causes send delays with the RFM95 on and eating power

      //Do here whatever needs to be done after each of the sleepcycle (e.g. check for a condition to break for send or take measurements for mean values etc.)
    }

    //Instead of the for-loop, a SLEEP_FOREVER can be used with waking by interrupt (if defined)
    //LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF); //Also only add e.g. 1 minute after wake to time0_overflow_count if this is used
    //os_getTime();   //VERY IMPORTANT after sleep to update os_time and not cause txbeg and os_time out of sync which causes send delays with the RFM95 on and eating power 

    Serial.begin(115200);
    Serial.println(F("... done sleeping")); 

    powerdown=false;
    measure();  //get some data
    os_setTimedCallback(&sendjob, os_getTime() + ms2osticks(10), do_send);  //do a send
  }

} //loop


void measure() {
  //Assumes you have a voltage divider at A0. Preferrably one that does not drain battery, like this one:
  //https://jeelabs.org/2013/05/16/measuring-the-battery-without-draining-it/
  Vbat = analogRead(A0) / 1024.0 * 3300 * 2;  //Assuming you run on 3.3V
}


Sleep mode LowPower.h
(Russlan) #45

Hi, i tried your sleepmode and it worked perfectly.
But i have a question about the battery measuring. What numbers do you get for analogRead(A0)? I am trying to debuggin, thats why i need some numbers i can compare with.


(Amedee) #46

It can be anything depending on your voltage divider and you reference voltage (1.1v is typically the only one usable on battery powered AVR unless you have a regulator)


(Russlan) #47

i use a arduino pro mini and my circuit looks like this. I operate with 3.3 V. The only thing i changed in code was the Pin. And yes, i am using the 1.1 V

grafik


(Miwo) #48

Hi, you should get values around 1024 with your setup on the arduino pro mini (3.3V*(10 kOhm/30 kOhm)*1024/1.1V) if VCC really is 3.3V and you use the 1.1V reference setting using analogReference (INTERNAL);.
If you keep the default, or analogReference (DEFAULT); external VCC (3.3V) reference, you should see about 340.

I typically use the default reference (VCC) as I usually drive the Arduinos by LiPo Battery with a regulator or with an upconverter from an AA-Battery to 3.3V which for my purposes gives me sufficiently precise 3.3V to get me something to measure the Battery (or solar cell voltages) against.
See http://www.gammon.com.au/adc for details on the ADC and reference voltages.

As Amedee says, if you use e.g. 4.1 V on VCC and use a regulator, you will see higher values, or in your case still 1024.

However, depending what your needs are, the 30 kOhms you have between VCC and GND might drain your battery (if you are running from battery, of course) unnecessarily as it will add another 100 uA of wasted amperage which sounds not like a lot but actually is compared to a bare sleeping Pro Mini (without LED and any sensors attached). If you have the Power-LED still connected (ca. 2 mA) , it does no longer matter.

Having said that, this is why I love the jeelabs-setup I mentioned in my code example. (https://jeelabs.org/2013/05/16/measuring-the-battery-without-draining-it/) using 2x 10 MOhm resistors (or anything below but the higher, the better, if you don’t have 10 MOhm resistors) and a 0.1 uF capacitor in parallel from PIN to GND a lot better than 10 kOhm Resistors.
This saves you a lot of power without degrading precision for just measuring the battery voltage.


(Amedee) #49

I concur…

With a 1/3rd divider and 1.1V reference you will max out unless you feed less than 3.3V, and you will waste power.

Now…
… if you use a Atmel 328p (Pro Mini) you don’t really need all that, just read the voltage from the chip (see here)


(Miwo) #50

Very good remark! :+1:
Yes, if you want to measure VCC and power directly into the VCC Pin (not using the regulator, otherwise it is essentially pointless as it is “always” 3.3V).
No, if you want to measure VBAT or anything else like I wanted in my example.