EmonTx on 5v input - change burden resistors?

Hi All

I'm very new to this, so go easy on me!

This: http://openenergymonitor.org/emon/modules/emontx/features

says that 5v inputs will be regulated down to 3.3v

however this: http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface

says that Arduino needs burden resistors changing between 5/3.3v inputs.

EmonTx is supplied with 18 ohms, the burden resistor for 3.3v supply.

I am going to run my EmonTx on 5v USB power, so do I either:

A: assume all is OK as the regulator is bringing the voltage down to 3.3v so 18 ohms is correct..  OR

B: change my burden resistors to 33 ohms?

 

I hope the answer is A!

 

Thanks

 

Paul Reed's picture

Re: EmonTx on 5v input - change burden resistors?

The answer is A.

If you read the link that you quoted above under 'Power';

When powering the unit with 5V through the USB or FTDI header the on-board voltage regulator will reduce the voltage to 3.3V.

...and that provides the voltage to the CT's. See http://solderpad.com/openenergymon/emontx/ for the circuit diagram.

Paul

phildabeast's picture

Re: EmonTx on 5v input - change burden resistors?

Perfect, Thanks Paul

:-)

Robert Wall's picture

Re: EmonTx on 5v input - change burden resistors?

Adding to what Paul said, the BB article refers to an Arduino Board which does indeed run the ATmega processor on 5 V. The problem comes from casual use of "Arduino" to mean both the ATmel ATmega processor (which strictly speaking it isn't) and the Arduino PCB that uses the Atmel processor (which is correct).

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