SP with free tone app on the cell
way cool!
now I need to find an iOS app and replicate this
Whats the current supplied to the coil?
If you have a multmeter you can measure it. Measure DC current. The number should be about half what is actually being driven through the coil since DC current for an AC waveform unless your multimeter is funny somehow should be half the actual current given the 50% duty cycle of the waveform. Average current is across the whole waveform and since you’re only driving it for half the waveform, the average will show up as half the current actually flowing when the coil is driven.
SP coils are notoriously low resistance. IF they’re 2 Ohms, its a lot. That means that if you put a single 1.5V battery (DC) across the coil, assuming it is 2Ohms, the DC current flowing would be 3/4 AMP. You MUST seriously current limit the drive to the coil to get the current low enough so as not to kill your cell phone battery. If you can’t do this by varying the output amplitude of your tone generator app you need to install a series current limiting resistor of the correct value to make it so.
Resistance = voltage/current.
For example, if your tone app is putting out 1V peak and you want 10 milliamps through the coil (which would be 5 milliamps battery drain for the above stated reason) and your coil measures say 2 Ohms, compute the total resistance required by doing a voltage/current thing (10 ma must be fractional as in 0.01) and then subtract the coil resistance from this. This is the resistor value you need in series with one of the coil wires to limit the current to what you want.
Resistance = 1v/0.01amp = 100 Ohms – 2 Ohms (coil) = 98 Ohms (resistor you need to put in series – find something close and higher in value).
Just as a jog, for a 2Ohm coil where you want 10 milliamps through it, the voltage you need to put across the coil to get it would be
Voltage = current * resistance = 0.01 * 2 = 0.02V – yup, 2 HUNDREDTHS of a volt does it (a.k.a 20 millivolts)!!!
Current above is the instantaneous current you want flowing through the coil when the positive half cycle of the pulse waveform happens and current starts flowing. Battery current consumption will be half this number for the above stated reason.
Simple just not obvious as usual.
All I know is that I’m pushing a 15hz square wave freq…I haven’t tried making my own SP yet this one is from Ben Morton.
