# Current and wattage monitoring.

First let me start by saying I am new to Arduino's. I am a HAM Radio repairman my current project is a monitor for a linear amplifier. I want a arduino to display via LCD the current being drawn by said amp also the HF (10 Meter Band) output wattage. What would I need to get these signals to a arduino level.

Basically do a Google search for:- "high side current monitoring" to see all the options. Basically you have to monitor the current by measuring the volts drop across a small series resistor, then you have to remove the DC level to get it into the 0 to 5v range suitable for feeding into an Arduino.

73's de G8HBR

It depends exactly where you want to measure. If you can hook into the DC-filtered part of the amp then you can use a high-side current monitor or (simpler but less efficient) low-ohm sense resistor to monitor the current. If you're trying to get current measurements right at the amplifier output you're going to have more trouble due to the bandwidth requirements.

For the output wattage, probably easiest is to measure peak voltage and assume a known antenna impedance, then derive output wattage from that. An averaging peak detector circuit would be a good start.

It all depends upon the exact circuitry of course. In all cases you want to reduce any voltage measurements you are making to 5V or less.

Does any one have any circuits for the current sense. I can hook into the DC supply. This system doesnt need to be extremely accurate so the low ohm method will do I do not understand this works with the arduino.

What kind of voltages and currents are the DC supply going to be providing?

The supply is 13.8V DC and The linear Amp should draw somewhere between 15-25 amps the supply is rated to 85 amps

Now that's a power supply! :) At those currents a sense resistor is going to be a huge waste of power. I'd suggest a Hall effect current sensor, like the Allegro ACS712ELCTR-30A-T. Here's an example circuit that will provide an analog output voltage proportional to the current (66mV/A so 10A of current will provide a 0.66V output). This analog voltage can then be read by the Arduino board A/D input as a number, printed to the screen, etc.

Thank you soo much for your time.

Sparkfun (sparkfun.com) sells a sensor for about \$20 that I think will handle your needs: it has an extremely-low resistance precision shunt, and an op-amp that scales voltage and current (up to about 50V and 80A, iirc) to ranges suitable to Arduino A/D.

Ran