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I am struggling to find the proper circuit design layout to properly power the ADH8066 GSM module and communicate with my Arduino.

The ADH8066 requires a 4V power supply and can have a brief spike of up to 2A during the start of communication.

I have been able to use an adjustable voltage regulator to provide a clean 4V from my power supply, but I have been informed on a forum that I must also use capacitors to cover the amperage spikes (since the Arduino cannot permit that high of amperage to be pulled, even if the power supply supports that rating).

I am a new entrant into the EE space, so I am trying to determine the ideal capacitors to purchase and where they need to be introduced into my circuit.

If anyone has had experience getting the ADH8066 to operate (even if they have a different circuit design than I'm referencing above), any insight into the proper layout would be immensely helpful.

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Well I assume you're not powering this guy via USB if you expect it to pull 2A occasionally. In that case, I guess you're using a wall adapter? If so then just power the sensor directly: PSU --> regulator --> sensor and then the arduino doesn't care how much current it pulls. Just make sure you connect the GND of your regulator to the GND on your arduino or else your signal line from sensor to arduino won't be interpreted correctly. – Nick Halden Jul 20 '11 at 14:49
Thanks JGord. Yes, I am using a 9V/2A wall adapter. This module will be part of a larger system of components (an LCD, etc) and eventually would need to fit into an enclosure. So given those points, am I reading you correctly that I connect the power through the module first and then route the appropriate amount of voltage through the Arduino in order to power the whole system from a single wall adapter? – Tom M. Jul 20 '11 at 15:04
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Not quite what I had in mind. Just power the arduino and the module separately from the same power supply (in parallel). So PSU --> reg --> module AND ALSO PSU --> arduino (which has a 5V reg on it if you go through the VIN pin i believe... check that). – Nick Halden Jul 20 '11 at 15:09

2 Answers

up vote 2 down vote

You are saying that the device requires 4V and bursts of current up to 2A, and that your Arduino isn't capable of supplying that. So don't try to make it.

Either get a separate power supply for each device, or a bigger beafier one that can handle both. I don't know what voltage the Arduino wants, so I'll assume 5V. Get a 2.5A or more 5V supply, power the Arduino from it directly, and power the GSM module from it with a 4V LDO regulator.

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OP is using a 9V 2A wall adapter, stated in his comment. – Jon L Jul 20 '11 at 16:39
I assumed that he meant that there may be 2A spikes, which is common enough in many applications, whether a motor startup or RF TX burst ... . I assumed a very short spike for my example. HMMV and I gave a simple formula for other assumptions. Get's into significant capacitance if bursts over 10's of mS are involved. – Russell McMahon Jul 20 '11 at 19:32
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A capacitor will change voltageby (~=) 1 volt per farad per amp drawn for one second. Putting that into useful terms.

  • V = t x i / C ... (1)

  • C = t x I / V ... (2)

    1. tells you how "deep" the spike will be (very approximately)

2.tells you how much capacitance you need to achieve no more than a certain voltage dip for a given current for a given time.

There are a number of variable that you will need to know. For an axample lets assume some value

  • V = acceptabe dip = 0.5 Volt

  • I = current spike = 10A

  • t = duration of spike - set to 10 uS.

Then

C = t x I / V = 10E-6 s x 2A / 0.5 V = 40E-6 Farad = 40 microfarad = 40 uF.

So a 100 uF capacitor would probably do well enough.

Place from output of regulator to ground IF regulator spec sheet allows this. Current will be taken from cap and regulator will not "see" it. This should be OK in most cases.

If output location not allowed by regulator spec, place from regulator input to ground. Regulator must now be able to handle the current pulse. Annoying as it may mean need to overdimension regulator.

Use low ESR cap. Ceramic if affordable. Solid Aluminum is good. Wet electrolytic less good. Tantalum superb BUT if you overvolt it with a spike it dies with a vengeance (and smoke flame noise and smell.). Alumin eletrolytic plus a say 10 uF ceramic in parallel. is probably good.

Note that above figures are for assumed values. Adjust to suit.

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