Battery Sensor with stepup and on/off transistor

[m26872]

Anyone else but me that have heard an annoying audible noise from the 5V step-up? Somehow the quality of the 5V step-up seems a little worse from my experience (don't power the nRF via step-down from this). But, it still can't explain the incredibly high (and continuously increasing) price tag on the 3.3 V step-up, which is a mystery.

btw I think powering the sensors only as in this thread is really interesting. Even if it's not always economical due to start up time, it could be used for sensors active part time of day. E.g. I'm planning a battery powered PIR only active during night time and expect it to survive longer with a step-up compared to without.

[Suresh Mali]

@n3ro Why would you need a step up for DHT, I am running DHT11 on 3.3v and it work fine.

[n3ro]

@Suresh-Mali My sensor node is powered with two AAA Batts. Over the time the voltage drops down to 1,9v.

The DHT only works with ~3v. so i need the stepup only to power the dht

i use this setup with my multisensor nodes.
http://forum.mysensors.org/topic/1514/multisensor_pir_dht_ldr_battery/3

Without transistor the battery is drained in ~2 month (black line)
with transistors in ~10 month

[Suresh Mali]

@n3ro Gr8, makes sense.:+1:

[n3ro]

Hey togehter,

is a battery drain graph like this normal with alkaline batteries?

regards,
n3ro

[mfalkvidd]

@n3ro said:

is a battery drain graph like this normal with alkaline batteries?

If you mean the sudden drop at the end, the answer is yes. This is called a S curve because it looks like a (very stretched) S. That's the typical behavior of most batteries.

[GertSanders]

The fact that you drain the battery in less then 2 months is probably due to the presence detection. I'm assumung this is using passive IR and is always on ? As mentioned by @mfalkvidd the shape is normal.
I use the breakout for SI7021 from Aliexpress and these use very little current. Also, there is no need for a step up, as this sensor works down to 1.8V. For light detection I use a LDR and 1MOhm resistor combination connected to a digital pin for power and analog pin for measuring. Works nicely because I let it settle (I first call the SI7021 to get the temperature and check the battery voltage, then I measure the analog value of the LDR. I only need relative values for light, so LDR is more then accurate enough for me.

[n3ro]

@GertSanders
thx :)

I have just ordered some SI7021 for testing.

My Pir sensors are these ones:
http://www.amazon.de/gp/product/B008EGH3FM

50 Mikroampere

i dont know if this is aktive or passiv :-/

regards,
n3ro

[GertSanders]

It's a passive IR module, and using 50uA, which is about 5 times the average consumption of my temperature/humidity sensors (between 8 and 11 uA depending on the amount of message resends needed).

The nice thing about the module you use is the low voltage it needs to work (0.8V <-> 9V).

[n3ro]

@GertSanders said:

(0.8V <-> 9V)

Yes. I had a few problems with the 5v PIRs. That's why I ordered this.

[abmantis]

@n3ro Couldn't you power the step-up from one of the arduino's digital pins? Then set the pin to HIGH/LOW to power the sensor on/off?
Maybe it draws too much power?