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I have a circuit composed of Arduino Mini Pro 3.3V and GY-GPS6MV2 (GPS Ublox NEO-6M). I have tried to power it with 3 different sources:

  1. 3xAA NiMH in serie connected to RAW pin of Arduino and using its VCC pin to power GPS
  2. DC/DC Step-up power converter powered by 2x2 serial-parallel NiMH AA connected to VCC of the Arduino
  3. (high current) USB via FT232RL FTDI 3.3V

If GPS module is not attached then measured VCC is in all three cases almost 3.3V but once I attach the module then it drops again in all cases to around 3.0V (it varies a bit depending on how much current does GPS module just need).

If I was powering it with USB then in some cases GPS module was restarting repeately because it had not enough voltage. I've fixed this by bypassing built-in voltage reglator of the GPS module.

Input current of the GPS module is measured max 70mA which I think is not that much. Input current of the whole circuit is then around 100mA (so it is 30mA for Arduino + some other parts).

Why is there that big voltage drop and why I observe it in all three cases? I don't think that 100mA is that big current for any of the three powering solutions.

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  • \$\begingroup\$ You know your GPS module has a built in regulator and won't work if you feed it 3V3, right? It seems you know it but you know, just to be sure. \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 7:43
  • \$\begingroup\$ Sure I know it. I have mentioned it in my question. It works if I feed it with 3.3V unless it consumes too much current and so dropping voltage to less than 2.9V which I observed this only in case of powering it from USB. Therefore I've bypassed that internal voltage regulator as mentioned in my answer. Currently the circuit works but I don't like it operates on 3.0V as it should be 3.3V. I don't know how stable it will be at 3.0V. \$\endgroup\$ – Martin Ždila Jul 18 '14 at 7:50
  • \$\begingroup\$ Sorry I did not see that part. So let me get this straight, you are powering the GPS module directly with 5-ish V or through the arduino regulator? \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 8:09
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    \$\begingroup\$ I think we might have a different concept of "detailed description". Anyway, I see that adding capacitors did not do the trick, so you can either add details or wait for someone who had your same problem. Something from the top of my mind: how did you measure current consumption and voltages? What batteries are we speaking of? What are this VCC/RAW pins? GPS datasheet anyone? \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 8:32
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    \$\begingroup\$ In option 3) you seem to use the 3V3 output of the FT232RL chip, is rated for only 50 mA. \$\endgroup\$ – Wouter van Ooijen Jul 18 '14 at 8:38
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Have you considered the peak current taken by the GPS module - it will take short pulses of current in the order of a couple of amps. Average is one thing but peak requirements (even though very short in duration) can cause your regulator circuit to get out of shape. Try putting a big decoupling capacitor (maybe 1000uF) on the power terminals to the GPS.

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  • \$\begingroup\$ Actually I had there 330µF capacitor. For sure now I added 2200µF but I see there no difference in measurements. \$\endgroup\$ – Martin Ždila Jul 18 '14 at 8:21
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    \$\begingroup\$ The 2200uF might have a very poor effective series resistance and make no inroads into your problem. This question has been asked and answered before so you might consider searching for this on SE.EE \$\endgroup\$ – Andy aka Jul 18 '14 at 8:37
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Looks like the internal regulator of Arduino cannot handle more current. If the GPS module runs on 3.3V, its own regulators needs something more than 3.3V at the input due to dropout.

Thus, power the GPS module from the power source (voltage > 3.3V) directly while keeping its regulator enabled.

Alternatively, replace the internal regulator of Arduino with a one that can handle higher current draw, bypass the internal regulator of GPS module and let it draw power from the new regulator.

It is good to give the schematic of Arduino a look to see if there is something else (e.g. protection resistor or fuse) that might be causing the drop.

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  • \$\begingroup\$ Thanks for the answer. Actually I would like to use alternative 2 in my product. Other two alternativew was just about to find out the problem with voltage drop but none of them has proven anything to me. But I am giving you +1 for the details. \$\endgroup\$ – Martin Ždila Jul 18 '14 at 9:17
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Here is a brief explanation on why none of your solutions will work.

1) While 3 well charged batteries might provide enough voltage to have the arduino linear regulator work it cannot provide enough current (read the spec), and the GPS regulator should be bypassed anyway, and to me it does not seem that you did so for option one.

2) Your DC-DC regulator is rated for low output currents when powered with voltages lower than 2.5V (read the spec). Also if two batteries should provide something around 2.5V the current drawn at 100mA@3V3=300mW might be quite high. If the DC DC has unit efficiency you are asking for something like 120-150mA@2.5-2.0V if you are lucky, that might well be too much for commercial NiMh batteries. I suspect the input voltage is falling quite low, thus limiting the DC-DC output current.

3) The FTDI board can provide a maximum of 50mA that is not enough for your needs (read the spec).

Since you say you want to use option two in your product I suggest you to use the four batteries in series instead of a 2s2p configuration, or even better just use the four batteries in series, power the arduino via the RAW pin and power the GPS through its own linear regulator. The last one is the low cost, low part count solution but it might not work due to the current request of your system, that might be too high.

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  • \$\begingroup\$ Thanks for the answer (+1). I am bypassing regulator also in the first alternative, but this does't solve the voltage dropout anyway. In second alternative I am using together 4 batteries - two pairs of serially connected baterries finally connected in parallel so they can provide doulbe current. Connecting them all serially would produce 5V that is too high for the DC-DC unit (limit is 3.3V). Anyway I will try to buy DC-DC unit with better parameters (goo.gl/87JdBc). \$\endgroup\$ – Martin Ždila Jul 18 '14 at 10:30
  • \$\begingroup\$ The other you linked is not good either, you need something that accepts 5V as input. \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 12:22
  • \$\begingroup\$ Could you please recommend me some exact part? Preferably something I can find on ebay/DX. Thanks. \$\endgroup\$ – Martin Ždila Jul 18 '14 at 12:38
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    \$\begingroup\$ Yes they should do, that's kind of an overshoot though. Why don't you just open a new question where you ask advice on how to power your setup? Be sure to include what power source you want to use (batteries) and all other needed informations, about onboard regulators, about things you might want to add to the arduino and please, please, please include links to the datasheets. \$\endgroup\$ – Vladimir Cravero Jul 18 '14 at 12:48
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    \$\begingroup\$ Done. electronics.stackexchange.com/questions/121844/… \$\endgroup\$ – Martin Ždila Jul 18 '14 at 13:24
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My circuit is built on breadboard. I have found out that breadboard itself has pretty high contact resistance and this is one of the main reasons of the voltage dropout when supplying power by DC/DC regulator (2).

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