user12102: I'm working to make a simple pedometer with Arduino, and after managing to find an algorithm that correctly finds the steps, I added a bluetooth extension (the overly popular and cheap JY-MCU) to check the steps via bluetooth.
I am facing a strange issue, though: when the bluetooth device is powered and waiting for a connection (red led blinking) the analog read function that reads data from the accelerometer goes crazy (thus the pedometer finds a step each second or so). When the bluetooth is powered down or connected to a device such as a mobile phone this doesn't happen.
Did anyone have this problem before? What could be the issue? My setup is easy, you can see it on the image.

I had other sensors as well but since the problem stays even when there are only those two connected I posted the bare minimum setup.
At first I thought I could use some kind of pull-ups to stabilise the signal, but I really have no idea on where to tie them and if they can really be helpful at all...
Any help is appreciated.

user4143: You can try decoupling the power for the bluetooth:

The resistor value should be tiny - 10Ω is a good value to use - don't go much higher than that.  The capacitor should be nice and big - I have shown 100µF, but bigger is better - whatever you have that's nice and big.  (Make sure you wire it the right way round - check which pin is marked as -)  You might also want to add a small capacitor (say 100nF) in parallel with the large one. 

12102: <p>I'm working to make a simple pedometer with Arduino, and after managing to find an algorithm that correctly finds the steps, I added a bluetooth extension (the overly popular and cheap JY-MCU) to check the steps via bluetooth.</p>
<p>I am facing a strange issue, though: when the bluetooth device is powered and waiting for a connection (red led blinking) the analog read function that reads data from the accelerometer goes crazy (thus the pedometer finds a step each second or so). When the bluetooth is powered down or connected to a device such as a mobile phone this doesn't happen.</p>
<p>Did anyone have this problem before? What could be the issue? My setup is easy, you can see it on the image.</p>
<p><a href="https://i.stack.imgur.com/PDG2n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PDG2n.png" alt="enter image description here" /></a></p>
<p>I had other sensors as well but since the problem stays even when there are only those two connected I posted the bare minimum setup.
At first I thought I could use some kind of pull-ups to stabilise the signal, but I really have no idea on where to tie them and if they can really be helpful at all...</p>
<p>Any help is appreciated.</p>
 4143: <p>You can try decoupling the power for the bluetooth:</p>

<p><a href="https://i.stack.imgur.com/unllb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/unllb.png" alt="enter image description here"></a></p>

<p>The resistor value should be tiny - 10Ω is a good value to use - don't go much higher than that.  The capacitor should be nice and big - I have shown 100µF, but bigger is better - whatever you have that's nice and big.  (Make sure you wire it the right way round - check which pin is marked as -)  You might also want to add a small capacitor (say 100nF) in parallel with the large one. </p>
