BLE 112 Current Fluctuation

[RoboTechEd]

Hi All!

I am designing a circuit using a BLE-112 (Bluetooth 4.0) chip and have noticed something very interesting that I was hoping people could explain. I am measuring the circuit's current and voltage, and it sits at a steady ~40mA. But if I physically move near the device I see current spikes of up to 5-6mA (I have noticed the more exhagerated the movements, the larger the spikes). The second I stop moving it settles back at the 40mA. I was curious as to what would cause this? I can reliably cause it, and can get a video if necessary.

[mikeselectricstuff]

Floating input pin?

[RoboTechEd]

Solderless breadboard?  That's probably your problem right there.

It is a solderless breadboard! But I cant imagine that my movements from 3 feet away for affect that. Especially considering it is on an ESD matt and I am not touching anything? I also am using solid core wire, and not those dodgy jumper wires most use. I should solder it up and see if anything changes.

Floating input pin?

I don't think its cause by anything floating. The current is whats changing, not the voltage. I do have pins though that are unassigned

[hamdi.tn]

Solderless breadboard is a problem for sure, floating input can cause excessive current consumption as well.
40mA is way too much for the module ! did you program it with sleep mode ?

[RoboTechEd]

Solderless breadboard is a problem for sure, floating input can cause excessive current consumption as well.
40mA is way too much for the module ! did you program it with sleep mode ?

No, I was just using som eexample code and not allowing it to sleep. It actually will not need to be low power consumption in the final product, so I am not concerning myself with it. I also have some LEDs, voltage regs (5 and 3), and logic level converters that are also running off of the supply, so that explains the 40mA. I just wouldn't expect those to cause the current to fluctuate based on my movement a meter away

[RoboTechEd]

Another thing that can cause that sort of thing is RF signals coming from the environment and being reflected / absorbed / blocked / enhanced by your body motion.  Like the case where you affect the reception of a weak station on a radio / TV by your body position.  That is more common in RF receivers, but if you have some semi high Z circuits that are picking up and rectifying RF from the environment it could cause it.

I will take it out and test it. I will place it in the middle of my room and see if location has an impact on it.

I have no other sensors in the circuit either. It consists of an Arduino Uno (PC powered), 3.3v and 5v linear reg, logic level converters, and my bluetooth chip. No sensors (yet).

Make all unassigned inputs outputs that are forced to 0 or something or use pull down resistors to ground any unused inputs.

I will have to do this! I couldnt imagine floating inputs would affect the current draw though. Im using an example program and I would assume they are all set to be pulled down/up, but I shouldn't be making assumptions - I'll check

Then test with a fan or flashlight or sound from your voice...If a blanket / sheet shields it then it might be air currents or light whereas if aluminium foil shields it then it might be e-field or RF.  If none of that shields it, maybe good old vibration.

All great test scenarios, I will be sure to test them when I get a chance. I was wondering if the Bluetooth beacon was measuring its own signals reflected, and were upping the output amplitude in that direction to compensate or something? Seems pretty far-fetched and complex though for a cheap chip.

[mikeselectricstuff]

I will have to do this! I couldnt imagine floating inputs would affect the current draw though.

They absolutely will, both due to partial conduction from an intermediate logic state, as well as possibly causing unintended wake-up from wake-on-change funcitonality.

Im using an example program and I would assume they are all set to be pulled down/up, but I shouldn't be making assumptions - I'll check

Don't assume - test!

A quick but often effective test is to run your finger round the pins and look for current draw changes. Mains hum will trigger floating pins.

A more thorough way is to measure current that flows when each unconnected pin is connected to supply & ground respectively to check that it has a pullup/pulldown. If you get less than a few tens of microamps then the pin is at risk of floating.