Need help with a basic oscillator circuit

I have a small project I've started and need some help with a very basic circuit. I am a fishing fanatic and reliable DC powered aerators are simply not available. I decided to convert an inexpensive AC fish tank aerator to DC. My first thought was to add a DC motor to drive the diaphragm pump, but a little thinking sent me in a different direction.

The AC pump motor consists of a small coil about 3/4" cubic. This is mounted on a magnetized iron core that is U-shaped. One arm of the U goes through the center and the other is on the side. Parallel to the face of the iron core, where it exits the top of the coil, is a magnet mounted on the end of a steel blade. The other end of the blade is mounted in rubber. When the pump is plugged in, the changing polarity of the magnetic field moves the magnet between the two arms of the iron core. This in turn moves the blade back and forth and the diaphragm pump is mounted in the middle of the blade and developes about a 2mm stroke.

I looked for micro inverters that I could rob the innards from and simply power the existing motor with batteries. Since the unit only consumes 1.5 watts, the smallest and cheapest inverters I could find were 50-100 times larger than I needed. This started me thinking further. An osillator in its simplest form is an inductor and a capacitor. Making a steel blade physically ocscillate does not require a clean, stable or precise signal. With the proper capacitor across the coil and a few D cells to power the unit, I would think this simple device would work quite well.

This is where all my thinking gets me into trouble. How do I size the capacitor? Would I need any other components? Am I about to set the house on fire? It's been about 25 years since I made a living in electronics, so I'm a little rusty. Any help you guys could offer on this project would really be appreciated.

You can't make an electronic oscillator without some sort of amplifier to make up for the losses in the L-C (inductor-capacitor) circuit and the losses due to the load (the diaphragm and the air moved by it). This would be difficult to design without having the coil in hand.
I wonder if you could use a vibrating motor from something like a cell phone or a pager. The eccentric weight on the motor shaft might be able to be used as a cam to move the diaphragm actuator.

EDIT: They may draw too much current to be practical if you are planning to use battery power, although D cells are pretty robust.

You could use a Hall effect sensor IC, or a second coil, placed near the moving magnet to provide a signal which varies in sympathy with the magnet movement. That signal can drive a simple amplifier which powers the existing coil. The whole system should then oscillate at some natural vibration frequency. No need for any tuning capacitor.

Thanks for the input Roff and alec_t. I've done a bit more homework since you posted and I see the fallacy in the idea. I guess what I really need for this project is a small inverter. The pump only requires 1.5 watts, so the inverter could be pretty small. The smallest inverter I can find is 120W. The closest thing I can find to a low wattage inverter are the driver circuits for battery operated flourescent lamps. Can anyone think of any other battery operated device that would have a low power inverter in its circuitry?

There's plenty of low power inverter circuits around on the web, usually consisting of a 555 oscillator, and not gate, 2 power transistors and a small mains step-down transformer being used in reverse as a step-up.
https://www.google.com.au/search?gcx=c&ix=c2&sourceid=chrome&ie=UTF-8&q=inverter+120v+schematic

Thanks for all the help. I think the use of an AC unit for my application is not the best choice. I found what promises to be the perfect pump for this application on Ebay. It is a small DC powered air pump used in the ballast control system of RC submarines. Who would have thunk it.

Nautica Rick said:

Thanks for all the help. I think the use of an AC unit for my application is not the best choice. I found what promises to be the perfect pump for this application on Ebay. It is a small DC powered air pump used in the ballast control system of RC submarines. Who would have thunk it.

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It might make your fish tank smell like bilge water.
Seriously, that sounds pretty cool.

After you've had a couple dozen pilchards in a five gallon bucket of mangrove water for a couple of hours, bilge water seems like a cool refreshing Perrier!

I got tired of the commercially available aerators either being built so cheaply they wont last or not being watertight and being destroyed by the first taste of saltwater. I had one stop working once and discovered a wave had half-filled it with seawater. The highly ionized water conducted electricity so well that the D cells got up to about 150F. I set out to build my own water tight aerator and it has evolved along the way. Dual pumps, rechargable Li Ion's and an unbreakable. watertight polycarbonate case should make for a very unique and durable unit.