# Electronic – LR oscillators (no capacitor)

inductoroscillator

How could a frequency be generated using one inductor and no capacitors? The waveform is unimportant. The active component could be transistors, logic gates (including schmitt triggers), or if necessary, op-amps. I would try to hack something together but I wonder if there are any elegant solutions that already exist. I have trawled the net and my books, and not found a thing. Thanks

Edit 1: Circuit 1 below is along the lines of the circuit suggested by Andy aka and Wouter van Ooijen. (Since the 555 timer is basically a schmitt trigger).

Circuit 1 seems like it could work. Assume ideal 5v logic. On power up, assume the schmitt output is 0v, and current flowing through R and L will be zero. The inverter's input will receive 0v. so the output will go high straight away. Then, as current starts flowing through L1 and R1, out of the schmitt's (high) output, the inverter's input will slowly rise. So far so good. When the schmitt's input rises enough, its output drops to 0v. At this point, its input is held at 5v, and as the current through R and L starts to fall, the voltage at the schmitt's input starts to fall. The problem: at this point, although the output of the schmitt is zero volts, current is still being drawn from it. This is because the inductor is acting a bit like a battery; it assumes a voltage that will maintain the current that was previously flowing through it (and R1), which was 5v. So to the schmitt trigger, this is equivalent to connecting the output to a -5V power rail via R1. Would this blow the schmitt trigger? (TTL? CMOS? 555?) simulate this circuit – Schematic created using CircuitLab 