Power issues with RFDuino

Question

I am new to hardware, I have always used plug and play shields to accomplish simple projects. A while back I purchased RGB LED Shutter Shades from Macetech. I got the hacker version thinking I would add a RFDuino and use that to power the glasses and receive commands from my iPhone. I found out that the glasses needed 5v and the RFDuino could only do 3V. So i used a Sainsmart Nano v3 to control the LED's and I added a RFDunio to receive commands from my iPhone, the RFDuino is powered by the Nano.

The issue I am having is that when Im using an external battery pack, the kind you use to charge your phone, I'm guessing the power is not consistent enough and the RFDuino drops its connection to my phone. When I run the glasses using my computers USB port I do not have that problem.

My question: Is there something I can add to my circuit to make this inconsistency with my power stop happening?

Answer 1

I am the designer of the RGB Shades and co-own macetech LLC. The RFDuino specifications claim only 18mA on transmit and receive, so there should not be a current draw issue from that module.

Known power issues with the RGB Shades include high current draw on startup. They can pulse about 1.3 amps (the blue flash) before your software sets them to a more reasonable level. Most USB power packs made today can handle 1.0 amps, some can supply more, but it's still common to find packs limited to 500mA...that would be one thing to check.

Since you are using your own code, please also note that our default code on the controller-included RGB Shades sets the maximum brightness to about one-quarter the actual maximum brightness of the LEDs. This is done to conserve power as well as reduce brightness to non-blinding levels. If your code is attempting to operate at normal brightness, please be aware the RGB Shades could draw up to 4 amps.

The best way to detect the problem would be to get a multimeter and compare the supply voltage when connected to your computer and when connected to the USB power pack.

• Sean Marraffa: Upon closer inspection both of the battery packs I have were 500mA. Im thinking that must be the issue. Thanks.

Answer 2

Wireless modules usually draw bursts of big currents in small amounts of time. For example ~1000mA for 1 uS (microseconds). Their overall power consumption can be low, however.

Perhaps, your external battery pack has a low current output which can not supply the burst current that RF module needs, but your PC is sufficient enough.

I would suggest adding capacitors (their size and amount depends, but put some big ones like 10000 uF in parallel and observe) so the burst current is compensated from the capacitors.

Make sure that those battery packs have enough current (hence, power) to power your RF module.

You can always use high rated battery packs such as LiPo's used in RC planes/copters, but be aware, they react badly when shorted so it may not be a good idea to use those batteries on your glasses...