Starting a battery powered stand alone project

I want to start a project that:

  1. Arduino smallest footprint
  2. Battery powered, hence standalone
  3. Battery module that can be piggy backed on to the arduino
  4. Case to hold both arduino and Battery module together
  5. Humidity sensor

Which arduino and Battery module do I need to buy?

Where will the humidity reading go?

Pro Mini.

Pro Mini with pilot LED resistor and voltage regulator removed, permitting minimal consumption in sleep.

Probably an 18650. How are you going to charge it?

  • Some sort of "zippy box" or electrical junction box.

Your pick. BME280?

Hello Paul, thank you for ur help.

I could live with as charging intervals of 1 hour, though anything above that would be better.

Perhaps I am approaching this problem the wrong way.
I am desperately trying to find a way to measure humidity as a way of knowing if urin is present inside a nappy.
My daughter is 20yrs old though she has a mental age of 1yr due to a deficiency of O2 during birth. This has left her incontinent as well as other obvious challenges.
I have been looking for a method to detect urin to assist us to know when her nappy needs changing. This would be useful during the day but especially during the night.

Hi - sorry to hear about the condition of your daughter, seems she is getting a lot of love and attention - kudos to you!

How would the system notify you was the question. You did not mention any output channel for the device.

This testing does not need to be running all the time, may be checking once a minute is enough - which should help with battery.

You don’t need 16MHz either - a 8Mhz / 3.3V Unit would also save battery

So 8MHz pro mini with removal of the led and regulator and powered with a NI-MH 3.6V or LI-ION 3.7V. If you can turn off the sensors, during sleep you’ll get a current draw of 1.5µA - that’s very low.

Measuring humidity can be done with wires and a variation of conductivity.

if you look for "smart diaper" you'll see ready made solutions.

Bed-wetting training systems are common.
They use the principle that urine is conductive.
Did you ask your health provider?

Thank you for ur response and help!

I would use a buzzer as soon as there is urin in the nappy. We have been trying for a long time to help her use the toilet, if she/we had some information as to when exactly to react i hope we may have more success, we would like to build up a better routine. She becomes nervous when we are anxiously waiting to catch the moment and use the toilet. I realise its not preventative, but its a first step in the right direction. Wish I had thought of the a lot earlier.

We live in Germany, we have good support though unfortunately this kind of problem is dealt with by using nappies. It is a good solution but we would like to improve the situation, as u can imagine urin is just the start of the problem also we need to prevent infections.

have you tried ready made solution ?

here is a couple first hit on Amazon for example

No, not yet. Though I will do so too, thanks!

The main problem will be "stool", she is fair skinned and gets rashes quickly and infections are a real problem. I am starting to get on in my years and worry about the future and hope i can help my daughter's future.
I want to be able to control the sensitivity of the sensor to not just catch urin. So urin will be the first step, if we could develop a routine based on the information from the measurements perhaps we could predict the moment of using the toilet more accurately.

OK - using branded devices with a CE label means they would have been tested for security too. You would not want a battery issue to add to the situation... I would definitely explore commercial offerings first and their capabilities.