# Can arduino handle my circuit? What do i need?

Hello,

I have built the below circuit with a breadboard. The bottom power supplies 5v is supplied by arduinos digital out port for 100ms and then off for 1 second.

The top battery is just a 9 volt battery.

I have an analog read coming from just above the 50 ohm resistor on the very right, and its signal pattern is displayed in the bottom right chart.

Basically, i want to be able to read a stream of voltages as the inductors flyback decays to zero.

The trouble is, when simulating the circuit with my software, using a 400uH coil (which is what i use in the real circuit) decays too quick, in microsecond territory, so i have to use a coil with larger inductance in the sim just so i can see the flyback decay pattern when i turn the circuit off.

Anyway, what would i need to do to make the flyback signal readable by arduino?

I currently recieve 0 when i run it as is so obviously the analogread is too slow to capture some of the flyback voltage.

Any help getting this working would be greatley appreciated.

If i could just take 3 or 4 samples before flyback voltage reaches 0 volts that would be good enough for now.

Thanks

By the way, its for a pulse induction metal detector

The time constant for an inductive circuit like yours is L/R where L is the inductance and R is the resistance. So you need to use lower value resistors (but that will increase current drain on the battery), or a higher value inductor (= more turns on your metal detector coil).

PS - bear in mind that R includes the resistance of the inductor itself. Currently, you have a time constant of about 20us. The Arduino ADC takes about 100us to take a reading in the standard configuration.

PS2: (a) inductance goes as the square of the number of turns
(b) alternatively, use an external fast DAC.

Great info Thanks for that

btw there is another way to measure the current decay of your L-R network that doesn't involve the ADC, which is to use the analog comparator instead. I think that's how this capacitance meter works https://www.sparkfun.com/products/9485? (it's measuring voltage rise or decay in a R-C network rather than current decay in a L-R network).

Yet another possibility: use the L-R network to make a free running oscillator with a 555 timer IC, and use the Arduino to measure the frequency.