well as it happens I am in the middle of a tutorial series on designing and building a modular power supply system that will include a Power Meter that will be ultimately micro controller based
What is your current skill set, I already have several tutorials up regarding controlling and monitoring the power supply and this will be good background info for your project
What are the specifications your trying to reach with your Ammeter ?, Range, Accuracy, other features ?
Provide this and any other info as to how far you have got and I will do my best to help you.
Have look at the ACS712 current monitor modules they measure both AC and DC currents. They are available in a range of current measurements, two I know of are a 5Amp module and a 30 Amp module. These can easily be linked to an Arduino and if you have a LCD display or 7 Segment display the measured current can easily be displayed. The ACS 712 modules are widely available, cheaply from China. Google "ACS 712 and Arduino", that will bring up a load of information to get you going.
If you are working with voltages like 110 VAC or 230 VAC PLEASE ensure you fully understand the dangers of these voltages and that you are competent to work with them.
