Rechargeable battery for posture sensor

Projects General Guidance
1

Hello everyone, I am trying to create a posture sensor similar to this one

Actually I have a prototype made of:

  • Arduino Nano
  • Gyro sensor (GY-521 with a MPU6050)
  • active buzzer (but I plan to replace it with a vibrating motor to make it more discrete)

I would like to place the sensor under the neck like the UpRight linked, sticking it with an adhesive or using it with a necklace. The gyro is used to detect when I am in a bad posture and it makes the buzzer sound (eventually the motor vibrate). The prototype is actually working.

Now I would like to add to the project a rechargeable battery, but it's one of my first project so I don't know how to move. I need a lightweight battery of course because otherwise the device will fall if I stick it, or will break my neck if I will use it with a necklace.

I have tought about 2 different solutions:

  • using a rechargeable battery, soldered or anyway not removable, with a on/off switch like this to turn off the device. That would mean adding something to recharge the battery, I don't know anything about this, but I think something like this. The problem in this case would be that the recharge module and the switch will take space into the device, and in addition I don't know anything about rechargeable batteries so I am little concerned about safety issues (like, can I charge it while the device is running? Can I charge while it is connected to the device?)

  • using a removable rechargeable battery, that would help me saving some space, which is essential because the device should be as little as possible, because I could just remove the battery when I want to recharge it or I want to turn off the device. The problem in this case would be that I am saving space without the switch and the module, but the only battery I have found to be easy removed and recharged would be this that is way too big (I think that the battery sould be something like this, which is 45mm x 25mm x 7mm), and in addittion is 9V which I don't need (I think the device could work on 3.3V, for sure on 5V)

Regarding the mAh needed I really don't know now, It would be ok if the sensor could run for 12 hours, but I don't know how much current it absorbs know, I have a multimeter but I think it's pointless to measure the current absorbed now without the vibrating motor

So I would like to have some advice: what do you think is the best solution? How would you do this? Is there some solution I haven't thought about? Thank you

EDIT: I measured the current absorbed with a 9V battery, it is 30mAh if the buzzer is not sounding, and 52mAH if it is sounding. The motor will absorb 60-100mAh depending on the volts, anyway I think that a battery with a capacity of 500mAh should be fine to make it lasts 12 hours

2

Pretty difficult to make any battery suggestions when you have no clue as to the requirements for the battery.

Use a piezo, such as in a smoke alarm, but add a plastic probe to contact the skin.

A Nano uses a lot of current to run and requires 5 volts. Look at some microcontroller that uses 3.3 or less voltage.

Paul

3

Why do you suggest a piezo?
Why a probe to contact the skin?

So Nano need 5V or more? Is there any battery that can help me?

4

matteo5v5:
Why do you suggest a piezo?
Why a probe to contact the skin?

So Nano need 5V or more? Is there any battery that can help me?

A piezo is small, 1 inch in diameter, is very thin, 1/8 inch or less. Direct contact with skin will quickly corrode the piezo surface.

You already know a nano needs 5 volts.

Paul

5

Actually I tought that the nano could run on 3.3V, so doing I research I think I'll need a Nano 33 IOT which has also the gyro integrated, right?

I can't understand why you suggest a piezo, I tought a piezo was something like a buzzer, so it makes a sound, but I would like to have something vibrate which is more discrete than something that produces a sound... I don't know if I have understood well, can you link something like the piezo that you are talking about? Thank you.

6

I edited the post adding the measurements of the current absorbed, with a 9V battery is 30mAh in standby, and should be around 130mAh when the motor is vibrating, so I think 500mAh should be ok to make it run 12 hours

7

matteo5v5:
Actually I tought that the nano could run on 3.3V, so doing I research I think I'll need a Nano 33 IOT which has also the gyro integrated, right?

I can't understand why you suggest a piezo, I tought a piezo was something like a buzzer, so it makes a sound, but I would like to have something vibrate which is more discrete than something that produces a sound... I don't know if I have understood well, can you link something like the piezo that you are talking about? Thank you.

A piezo responds with vibrations at the frequency of the alternating voltage you apply to it. If you use a low enough frequency, the piezo will vibrate and you won't hear it. Experiment!

Paul

8

So the piezo that you are talking about is a passive buzzer?

Any suggestion regarding the battery? Thank you.