DC power to sensor and arduino

Hi all,

I’ve followed this tutorial : Learn | OpenEnergyMonitor , and this seems to be working, but i would like to power up the arduino by using the 9v adapter also, but without messing up any sensor readings, how would i go about this ?

You cannot do that easily - and preserve the accuracy of the voltage readings.

The emonTx V3 does use the ac adapter as the power supply, but the current it is allowed to draw is strictly limited. If you want to look, the circuit is in the Wiki (via Resources). You have to use a half-wave rectifier because the adapter and ac input shares a common connection with the power supply, and so you cannot use a full-wave bridge rectifier because you end up shorting out part of the bridge.

The only other way is to use an operational amplifier with a differential input to provide isolation between the ac and dc sides of the bridge rectifier.

Even when you do that, you must remember that the d.c. smoothing capacitor takes a huge current for a very short time as it charges, and this, because of the transformer’s impedance, causes a big dip in the voltage that you’re trying to measure.

Thank you for your response, it does clear some questions i had…

I’m probably not the first guy trying to make the 9v adapter give power to the arduino and still using it for the voltage readings…

Since i’m very new to electronics, can you point me in the right direction so that i could implement a half-wave rectifier in this project ?

I have done. It’s used in the emonTx V3.

EmonTx v3.4 wiki → EmonTx V3.4 - OpenEnergyMonitor Wiki