Using SIM808 breakout board with Arduino on battery

Hi all,

I am prototyping a GPS tracker using Arduino Uno and this GPS&GPRSM shield: http://goo.gl/Uyyzk7 The GPS,GPRSM shield is working fine when powered trough the UNO.

I am now happy with the code for now, and want to do some further "mobile" testing.

But due to lack of space and power i want to use another SIM808 breakout board together with Arduino Mini pro. SIM808 breakout: http://goo.gl/x6WPnc

As known the SIMCOM modem needs 2A current peaks now and then. I was thinking about using a MOSFET to switch power completely ON & OFF to the SIM808 breakout to handle the high current peaks directly from the battery. But i wonder if there is possible to use one or few capacitors to handle the current peaks, so i could use for an example a step down buck converter rated for lets say 500mA. This is also wanted as the current on the battery drains during the lifetime.

I have searched the Arduino forum and also other forums, but i couldn't find a proper solution. What i would like was to make/order a small PCB with voltage regulator and also CAP`s to handel the high current peaks.

All suggestions is appreciated.

Cheers, Sindre

Mmm, I don't know about using capacitors to bridge the requirement for high amperage consumption.

What exactly do you mean by "now and then"? Even traditional power supplies with smoothing capacitors exhibit ripple voltages and that when being charged every 1/50th of a second so I'm just wonder what sort of capacitors you're thinking of to supply 1.5A?

Sure you can get mega uF capacitors with which you can start your car but then the size means you might as well have the proper sized battery and step down converter to begin with.

What's wrong with a couple of 18650 batteries and a step down buck converter? They will last quite some time whilst you do your "mobile testing".

I think we need more information why you are thinking of this as a solution. Size? Cost? Post back!

I will be using 2x 18650 batteries in series. Reason i want to use some capasitors for the power supply is to use a power supply not needing to support more than 500mA. Also the possibility to not needing the mosfet and powering directly from the Arduino. But thats maybe not a ideal solution.

So two 18650 batteries, in series, will be 3.7v x 2 = 7.4V which the Arduino UNO is capable of withstanding via the jack quite happily.

But now you are changing to an Arduino Pro Mini (which is either a 3.3V or 5v device, you haven't said) and which can take between 3.35V/5V - 12V just the same as the UNO. Is this right?

So why are you not just supplying the board with the 7.4V? What's all this about a MOSFET and 500mA?

I'm really confused at this point. Would it possible for you to explain what you think the problem is so I can understand your question?

Ralph_S_Bacon: So two 18650 batteries, in series, will be 3.7v x 2 = 7.4V which the Arduino UNO is capable of withstanding via the jack quite happily.

But now you are changing to an Arduino Pro Mini (which is either a 3.3V or 5v device, you haven't said) and which can take between 3.35V/5V - 12V just the same as the UNO. Is this right?

So why are you not just supplying the board with the 7.4V? What's all this about a MOSFET and 500mA?

I'm really confused at this point. Would it possible for you to explain what you think the problem is so I can understand your question?

The issue here is the SIMCOM 808 GPS/GPRSM module that will do current peaks up to 2A. Powering the Arduino itself isn't any issue... I know most GSM&GPS shields is powered fine trough the Arduino Uno... But this is not possible with this smaller SIM808 breakout board as it does this high current peaks, causing the SIM808 breakout board rebooting and not being able to start up when powered trough the Arduino. Therefore i am assuming the shields have built in some capacitors taking care of the current peaks, and therefore is powered fine trough the Arduino whilst my breakout board doesn't have these capacitors handling the current peaks.

Can you not supply the SIMCOM 808 GPS/GPRSM module separately from the Arduino - after all, it is getting its power from one of those pins on the shield now, right?

Even if it means using a small 2A step-down buck converter to reduce the 7.4V to 5V (which it does very efficiently)? It's also very cheap. The 18650 batteries will supply all the necessary current.

You can then disconnect the 5V power input pin to the shield to keep your power supplies separate (or, indeed, power both Arduino and SIMCOM module from the step-down converter).

Yes, separate the supplies. ProMini regulator is only good for 150mA. If the SIMCOM cards needs more, it has to come from elsewhere. I would look at switching regulators such as one of these http://www.digikey.com/product-search/en/power-supplies-board-mount/dc-dc-converters/4325599?k=recom&k=&pkeyword=recom&pv1471=43&FV=fff40042%2Cfff800df%2C15c0002%2C17d4003e&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 I am using this one in a project now to supply 5V from a 18-24V vehicle supply to power a '1284P, several shift registers, some MAX31865 chips (with 3.3V regulator fed from 5V), 5V to 3.3V buffers (SCK/MOSI/chip selects), 3.3V to 5V buffer (3.3V MISO back to 5V) and a CANBUS transceiver & driver. Might be something else too. http://www.digikey.com/product-detail/en/recom-power/R-78B5.0-1.0L/945-1053-ND/2256233

I have a SIM908 based GPS/GSM module on the card too, but that has it's own regulator that needs feeding, so the 18-24V was knocked down to 9V to feed it. Doesn't seem to need a lot of current, I haven't noticed the linear regulator getting hot.

(I should review my schematic to make sure I'm discussing things properly)