Hi,
I am trying to build a wireless sensor for my temperature log project. I had some issues at the beginning of playing with these small nRF24L01+ devices, but it seems I finally understood the stuff better and now I am able to make it work (RF24 lib -> getting started example with a bit of modification). When powering both arduinos from USB (Pro Micro connected to ftdi usb adaptor) it works perfectly.
I have currently arduino Uno r3 as a "ping out" device and one arduino Pro Micro 3.3V as a "pong back" device. I am trying to power the micro with 2xAA batteries and decided to use this kind of step up converter:
Input voltage 0.8 ~ 3.3V, output 3.3V
Maximum output current: 600 MA,
I can measure 3.34V from on the converter output. Unfortunately with this converter my "Pong back" Arduino Pro Micro with nrf24L01+ does not work properly - I can see only occasional successfully received responses on the other node. When I change the power supply to USB again, then it starts to work.
What can be wrong on the step up converter?
I did a test - connected 2xAA (2.9V) to the arduino pro micro with nrf24L01+ and it started to work perfectly!
So my wireless sensor can work when powered directly from 2xAA batteries with measured voltage of 2.9V but does not work (or works only very occasionally) when using the step up 3.3V converter .
I wanted to use the step up converter as it can produce enough current for powering the sensor even when battery's voltage is 1-1.5V, so I could use the batteries for longer time.
Can anybody suggest some hints? I already tried 1uF or 10uF electrolytic capacitor soldered on VCC and GND pins of nrf24l01+ when using the step up 3.3V converter, but no luck.
I wanted to use the step up converter as it can produce enough current for powering the sensor even when battery's voltage is 1-1.5V, so I could use the batteries for longer time.
You can't multiply voltage AND current. If you multiply the voltage by 2, you divide the current by 2. TANSTAAFL.
PaulS:
You can't multiply voltage AND current. If you multiply the voltage by 2, you divide the current by 2. TANSTAAFL.
Yes, but based on the specification of the step up converter: INPUT 1-1.5V, OUTPUT 3.3V 50-120MA;
So in case the input voltage is 1.5V, the step up converter will be able to deliver 3.3V at max 120mA which is enought for arduino + nrf24L01+
Or am I wrong?
I am sorry, but I am confused. So what you are trying to say is that it is impossible to create a step up converter which will convert 1.5V to 3.3V which I will be able to draw 120mA current from?
Then the specification would lie ("INPUT 1-1.5V, OUTPUT 3.3V 50-120MA;")
I think we just did not understand each other. If I am still wrong, then please be so kind and help me understand it better. Thx.
I did some further testing. I used 10uF electrolytic capacitor across vcc+gnd pins of nrf module. When I use the step up converter for powering both - arduino + nrf, I can't see any successful responses on the other node. But when I disconnect the + cable from step up converter and place a digital ampermeter across this + cable and the Vout pin of the step up converter, I can see there 24mA draw and I can seee successful responses on the other node. When I connect the + cable again to Cout of the step up converter, it again does not transmit any packets. So the ampermeter does some magic and makes this work Weird.
If I am still wrong, then please be so kind and help me understand it better.
You are. There is a certain amount of energy going into the system. There is a certain amount being lost to heat and other factors. What's not lost is the usable output.
You can not have more output than input. If you need 3.3V at 120 mA (0.396 watts), you MUST supply more than 0.396 watts as input. You can not, in this universe anyway, create energy using a boost converter.
I am sorry mr. PaulS, but I think we still did not understand each other.
I did not say I am creating energy via boost converter. What I was trying to say is:
Having 2xAA batteries with voltage of 3V as an input for the step up converter provides 3.3V on the output --> I can measure it via voltmeter.
Output of the step up converter can provide enough current for running arduino pro micro + nrf24L01+ (I measured it needs around 25-30mA in case it is running and transmitting)
Arduino and nrf24L01+ is powered on (there is 3.3V measured on it + it draws around 25mA from output of the step up converter).
I have problem that when using step up converter, it seems nrf24l01+ does not transmit or receive correctly - almost no packets are being successfully transmitted to the other node. When powering the arduino and nrf24l01+ directly from 2xAA batteries which have cca 2.9V it works perfectly.
So I just would like to know if I can do some modification to make nrf24l01+ work even when step up converter is used.
I did some testing as well to see whether I can draw enough current from step up converter. I connected some LED diodes to step up converter's 3.3V output, either without resistor or with and it confirms the step up converter can provide enough current when using 2xAA batteries (i measured current between output of the step up conv and led and also between batteries and input of the step up conv):
4xled without resistor:
current measured on output of the step up converter: 165mA
current measured on input of the step up converter: 900mA
1xled without resistor:
current measured on output of the step up converter: 95mA
current measured on input of the step up converter: 270mA
1xled with resistor:
current measured on output of the step up converter: 23mA
current measured on input of the step up converter: 38mA
So I can see we need more current on input of the converter than is drawn from the output - there has to be some loss when doing 3V to 3.3V conversion, of course - no doubt.
Why I wanted to use the step up converter - I thought it will be able to run the stuff even when batteries will have low voltage, like ~1.5-1.9V and I will run my wireless sensor for longer time. But maybe I am wrong. Anyway, I just wanted to know if somebody can help sorting out what is the problem. My suspicion is that there might be some ripples on the output of the converter which causes the problem, but I am not sure and also I am not sure if it can be filtered somehow.
I think I found the root cause. Quality of the boosted power output of the step up converter is not good. I found nice thread on this topic - Efficiency of Voltage Boosters | MySensors Forum
So either use only batteries to power the nrf24l01+ or find some high quality capacitor with low ESR.
I did an experiment today. Unfortunately I do not have oscilloscope, so I can only try and check. But - I removed 2 capacitors out of old adsl modem/router - capacitors are 470uF and 47uF marked as LOW ESR. I tried both. Using that 47uF worked parially - ~50% packet loss. Using 470uF capacitor 0% packet loss - works perfectly with the step up converter I have.
I tried also some capacitors with capacity of 1, 10, 100, 220 uF but those are not LOW ESR - at least it is nor marked on them and it did not work with them.
Anyway I am satisfied because I know that using proper high quality LOW ESR capacitor will solve the issue. I just have to find some good one, or I will use that 470uF from router, but its size is quite big, so better to find some smaller one which wil work.
Hi,
I will just summarize my experiences. I did not have much time past couple of months, but I finally got the stuff working. I had to buy these electrolytic capacitors - "470uF/ 6,3V R 105°C LEAGUER RPT Low-ESR" and put them across VCC and GND of nrf24l01+. But I had to solder them as shortest as possible to the VCC/GND pins (initially I soldered them with original, not shortened length of the leads andit did not work properly - so it looks to be pretty important). Using these capacitors with low esr made nrf24l01+ work reliable even when powered from step-up to 3.3V converter.
Wireless transmission works properly from input voltage 3V (input voltage to the step-up converter) to 0.8V. So yes, you are able to convert ~0.9V from almost discharged 2xAA batteries to 3.3V using the step up converter I mentioned before. When voltage of the batteries was 0.8V I measured current drawn from batteries ~250mA (quite much, it needs current to boost voltage to 3.3V).
Arduino pro mini+nrf24l01+DHT22 draws ~40mA from the step up converter.
Wireless transmission stops working when voltage of the batteries reaches ~0.7V. In this situation step up converter produces only ~2.75V output and it is not enough.
Further I will experiment with desoldering LED diodes from the converter and arduino and putting arduino and nrf24l01 to sleep and measuring the lifetime of batteries when sending values every ~5 or ~15 minutes.
Weird.