💬 Battery Powered Sensors

[zboblamont]

@sineverba I gave up trying to cross connect power controls directly and went for bistable telecoms relays, 100mW fire 30ms max latched stay open until you reverse signals from + & - pins. Works a treat, powered only for duration of latch....pity the sensor it controlled was shit, but hey ho....small steps

[sineverba]

@zboblamont

A bistable could cost more than entire node :D

But it could be an idea... instead of NPN. But remain my doubt.... for the moment, with node powered in this mode..... Am I in danger of burn battery / node / house? :(

[gohan]

If I were you I'd go for an I2C sensor that could also work at low voltage, this way you could also power the sensor via a digital pin and turn it off before entering the sleep function to save extra power.

[sineverba]

@gohan

What sensor do you use? Seems interesting the Bosch BM280 that has also the pressure but seems it wants the 3.3v...

[gohan]

I am testing SHT31 and BME280 but it is on the power hungry side and temperature is reading +0.5/+0.7 °C more, while the SHT31 is +-0.2°C

[zboblamont]

@sineverba I think the small latching Axicom 3v signal relay I used was around 2 euro, but they were sold in packs of 10, so expensive if no use for the other 9 :) The objective was low current low voltage short power duration, I found that the enable pin for the booster used more power when system was sleeping... switching the 5v booster by relay ensured no current leakage, 2 pins from the Arduino to control it, 30mA for 30ms to open, same to close it, as and when required to power the 5v ultrasonic... Arduino had it's own battery pack and booster but spends most of it's time in deep sleep so power consumption is peanuts.

[sineverba]

@zboblamont
Do you want post your schema // picture of your node? Thank you in advance :)

[zboblamont]

@sineverba None are finished, as waiting on the replacement ultrasonic to arrive. I posted photos of the original booster and JSN board at https://forum.mysensors.org/topic/4810/distance-sensor/43
when seeking opinions on potential noise issues. The tiny relay is also shown there.
The external nodes will all be Whisper Nodes (essentially a customised pro-mini), 2 have RTCs on board to take ultrasonic readings on two tanks, the rest respond to events.

[sineverba]

Atmega on breadboard, 8MHZ, no Xtal, BOD disabled.

I have a question and an issue.

This is exactly the breadboard (missing only the NRF, connected direct to the battery and not to the stepup and NRF has the 4.7mF capacitor and works very well on every other node).

This is my sketch > https://pastebin.com/raw/6Kxm238q

1. Can I remove one of the two 104 capacitors? Or I need both? Atmega feeded directly from battery, I remember.

2. With this setup, the node *doesn't trasmit and if I connect the serial (via FTDI232) Atmega floods it with strange characters and doesn't stop (I did try all the bauds, but default is 115200). The leds on FTDI232 blinks continuosly, 1 blink 1 strange chars printed on monitor serial.

2a) If I remove totally the ground between rails or remove totally the booster (so, for breviti, I don't give anymore power to the DHT22) the node trasmits very well (of course only the voltage) and serial works

2b) If I feed the node with 3.3v (e.g. from the FTDI232) the node transmits and serial is all ok.

At the end, seems that DHT 22 (rated for max 6V) doesn't want the 4.92V OR Atmega crash with this voltage.

PS I have the stepup to 5V 'case I did wrong the order..... :)

Thank you to all!

[mfalkvidd]

@sineverba your wiring looks quite odd. Especially compared to https://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/overview
Where did you find the wiring guide?

[sineverba]

@mfalkvidd do u mean the DHT? I can assire you that resistor is between data and VCC ;-) maybe semms strange for need of arrangement on frtzing....... in effect at 3,3 it works and it works in another noce (at 3,3) i would understand because at 5v it doesnt works and serial is flooded ...... I could also post a picture of real breadboard :-)

Thank you!

[mfalkvidd]

@sineverba yes, you're right. It looks a bit different but the connections are equivalent. Sorry for the confusion.

[sineverba]

@mfalkvidd no problem ! I can understand the difficult to understand schemas of other people ;-) do you nave btw somw idea for my issues and queation (if I can remove a caos, for example).... Thank you

[mfalkvidd]

@sineverba sorry, I don't. I have no experience with the bare atmega.

[Oliviakrk]

How about using rechargeable batteries instead of alkaline? They would be 1.2V instead of 1.5. vmax would be 2.8V ?

[sineverba]

@Oliviakrk
I use recheargeable. At full charge both are 2.74...
DHT22 at 2.74 doesn't read. It is rated for 3.3v - 6v

[Oliviakrk]

@sineverba
Yes, so a stepup before DHT 22 is required. And it works...But..I have issues with measuring battery level.

int batteryPcnt = sensorValue / 10;

Always gives something around 74-77%. Even if I use batteries straight of the charger (Panasonic/Sanyo Enelops, which are 1,3 -1,4V when taken of the charger)

[selvakn]

There is minor correction in the battery level measurement calculation. It should be 1.1 * (1 * 10^6 + 470 * 10^3) / (470 * 10^3) = 3.44V

[gohan]

@Oliviakrk Look in comments in the code

// 3.44/1023 = Volts per bit = 0.003363075

if your batteries put out a total of 2.8V the voltage divider is set to use a Vmax of 3.44V (that suits the alkaline batteries), that is probably why. If you want you could change the voltage divider for a lower Vmax

[FatBeard]

@sundberg84 To give you an update. I've changed from a dht22 sensor to a bme280 i2c sensor. The sensor is running off a4 and 5 and power is gotten directory from 2aa batteries. My original problem is gone in that it's working fine as a mysensors node. My issue though is when in sleep mode, i'm running at 1ma, when i would expect to be down in the low ua area. Any thoughts? The code i'm using is based off of this thread: https://forum.mysensors.org/topic/3816/bme280-temp-humidity-pressure-sensor/5