![]() To make it even more similar to a sine wave, we use the Phase-correct PWM. There is a trick that can be done: the two outputs of a timer can be run in opposite phase, by inverting one of the outputs. To run the coil most effectively, we’d like to use a true AC source. This is high enough that the Arduino does not go into overcurrent. We produce a signal with a frequency of 516kHz, resulting in an impedance of 2pi*f*L=275Ohm. So for N=20 and R=0.0425 gives L=85muH, which was confirmed with the component tester. The self-inductance of this type of coil with N windings and a radius R is ~5muH * N^2 * R. I used a paper roll of 8.5cm diameter and enameled wire of 0.13mm diameter to make 2 coils: the primary with 20 turns, the secondary with 50 turns. A coil with a high frequency signal can transfer power to another nearby coil through induction, without electrical contact.įirst prepare the coils. It is not uncommon to charge a smart watch without cables, but the same can easily be part of an Arduino project. A second independent DAC channel can be run with timer1 on pin 10. ![]() In the example, the DAC output is steered with a potentiometer. To avoid that, it can be buffered with an opamp, or another combination of R and C can be chosen, for example 1kOhm with 10muF. ![]() Note that this DAC has a very high output impedance (10kOhm), so the voltage will drop significantly if it draws current. The peak-to-peak ripple is at most 5V*0.5*T/(RC)=16mV, which is considered sufficient here. If we use a 1muF capacitor and a 10kOhm resistor, RC=10ms. The period we get for a 10-bit precision is 1024/16MHz= 64mus. The time-scale of the RC circuit should be much larger than the period of the PWM signal to reduce the ripple. The RC circuit is a first-order low-pass filter and it will have some ripple. The resolution of the 8-bit timers would be 5V/256=20mV, so we opt for Timer1 to get 10-bit resolution. The characteristics are determined by the PWM frequency and the values of the resistor and capacitor. A capacitor is connected through a resistor to a PWM pin. With just one capacitor and resistor, timer1 can be used to create an analog voltage with a resolution of 5mV or better.Ī low-pass filter can ‘average’ the PWM signal to an analog voltage. ![]() Some modules take an analog voltage to regulate a parameter (display contrast, detection threshold etc). The Arduino does not have a true analog output. ![]()
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