Years and years ago I did an analog "Warning Chime/CPU Monitor for Automotive Applications", which provided CPU POR functions and chime/alarm sounds in GM products. The chime sound was cleaner than the original bar "clacker". ...Jim Thompson
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
I don't get all the sniping. John posted a circuit--it was cute. Single-transistor (if that mattered) for a single resonant mode, plus extra optional modes if you want to simulate a real bell's complexities.
Not exactly what the OP asked for, but that's how he (the OP) discovers choices and alternatives. He may not've known about the extra modes' importance to realistic bell sounds. If the OP's dead set on a twin-tee, he'll say so.
There are bigger, more important things going on in the country than picking on John.
This is kind of a cute circuit. I first designed it when I needed a very frequency and amplitude-stable sine wave to drive a Talyvel LVDT-like inclinometer, part of the Boresight Alignment Kit for the C5A. We had to measure level to arc-seconds of accuracy.
It's a transformer with a resonant tank in the collector and a positive feedback drive winding into the emitter. The emitter feedback is just a couple of tenths of a volt p-p.
The cool thing is that the collector swing is almost exactly 2xVcc peak-to-peak. As the amplitude builds up, at the negative swing peak the emitter goes a little bit negative, to get out of the way, and the collector swings to just about ground. That forward-biases the c-b junction and discharges the base cap, reducing transistor base current hence gain. So it has a built-in peak detecting AGC amplitude levelling loop with close to zero TC. All from 5 parts. Or sometimes six.
I tested the system on a 55 gallon drum full of sand, with a huge steel plate on top. We built a platform that pivoted on ball bearings and we moved a long lever arm with a micrometer, to tweak the sensor angle. I had to tell people not to walk nearby, because their weight would flex the concrete slab of the building.
I learned a bunch on this project: HeNe laser power supplies, synchronous detectors, optics. I've always sort of liked this oscillator.
With your explanation, the oscillator is much more attractive. Some folks can't stomach magnetics, perhaps that's part of the criticism. Anyway, ignore JF and JT when they get bitchy, it must be something they ate, or is age catching up with 'em?
Our old friend, Tony Williams, R.I.P., would have been pleased.
. John Larkin's LC oscillator, supply-V sets amplitude . _________________ . | | | . | _|_C E || L . Rb --- E || . | | E || . | | * | || . | +-----' || . | | || . | C gnd || . +- B | || . _|_ E E || . --- | * | || . | +-----' || . gnd | . '--- out
Tell us more about the inductor / transformer, turns ratio, etc. Did I get the winding polarities right? I suppose you have to keep the emitter's reverse-voltage under say 5V breakdown, so 10Vpp max output? What are the prospects for making this into a high-power oscillator? Drive a speaker directly?