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The detector has been displaying x,y data pairs, and up until now I have been calculating the phase angles with a calculator. Now I have added an arctan routine so the detector can calculate the angles and display them with the x,y values.
Carl and Charles have both sent me op-amps to try. Charles' MPC602 arrived first so I tried it in place of the Motorola TL082 I have been using. The 602 output swings 4.6 volts before it starts to clip. This gives me about 30% more range on the input signal than I was getting before.
With these new additions I ran some more tests with the 5.3 coil. These are DC (non-motion) tests. In an air test it can ID a penny or dime at 5" from the coil but not at 7". At 5" the displayed angle jumps around within a 6° range. With the coil sitting on my concrete floor it can ID them at 3 inches but not 5". This is with the coil on the floor and the coin above the coil. With the coil one inch off the floor it can ID them at 5" but not as well as in the air test.
With the current configuration, the relative strengths of signals is: penny at 5" = 34, penny at 3" = 190, penny on the coil = 8000, coil 1" off the floor = 5300, coil on floor = 16300. So it was able to give a reasonable ID when the ground signal strength was about 100 times as strong as the coin signal.
I don't know if I am going to be able to squeeze any more performance out of this 10 bit A/D, but so far, I consider this a success.
At the beginning I did not have much choice about what to do first, because I needed a signal to look at before I could do anything else. Now that I have a signal, the options are opening up. It's hard to decide whether to work on an audio output so I can hear the all metal signal, or to start putting in motion filters.
I am surprised that the first resource I am running out of is program memory. I expected processor cycles or RAM to be more of a problem. So far I am using about 25% of the processor cycles, about 70% of the RAM and 90% of the program memory. I am going to have to change my programming style to trade off processor cycles for program memory. Of course that would happen at this stage anyway because I am about done with the high speed code and starting on the 60 Hz code where I don't have to worry about speed as much. But I may have to go back and re-write some of the high speed code to reclaim memory space.
Robert Hoolko
Carl and Charles have both sent me op-amps to try. Charles' MPC602 arrived first so I tried it in place of the Motorola TL082 I have been using. The 602 output swings 4.6 volts before it starts to clip. This gives me about 30% more range on the input signal than I was getting before.
With these new additions I ran some more tests with the 5.3 coil. These are DC (non-motion) tests. In an air test it can ID a penny or dime at 5" from the coil but not at 7". At 5" the displayed angle jumps around within a 6° range. With the coil sitting on my concrete floor it can ID them at 3 inches but not 5". This is with the coil on the floor and the coin above the coil. With the coil one inch off the floor it can ID them at 5" but not as well as in the air test.
With the current configuration, the relative strengths of signals is: penny at 5" = 34, penny at 3" = 190, penny on the coil = 8000, coil 1" off the floor = 5300, coil on floor = 16300. So it was able to give a reasonable ID when the ground signal strength was about 100 times as strong as the coin signal.
I don't know if I am going to be able to squeeze any more performance out of this 10 bit A/D, but so far, I consider this a success.
At the beginning I did not have much choice about what to do first, because I needed a signal to look at before I could do anything else. Now that I have a signal, the options are opening up. It's hard to decide whether to work on an audio output so I can hear the all metal signal, or to start putting in motion filters.
I am surprised that the first resource I am running out of is program memory. I expected processor cycles or RAM to be more of a problem. So far I am using about 25% of the processor cycles, about 70% of the RAM and 90% of the program memory. I am going to have to change my programming style to trade off processor cycles for program memory. Of course that would happen at this stage anyway because I am about done with the high speed code and starting on the 60 Hz code where I don't have to worry about speed as much. But I may have to go back and re-write some of the high speed code to reclaim memory space.
Robert Hoolko