Small Circuit Help Needed

I need some help developing a small circuit for a home project. I am looking to develop a circuit that operates on 12V, battery power, or even solar power if possible. I would like the device to fire a pulse to an electromagnet every 30-60 seconds using a timer or capacitor device. The electromagnet must be strong enough to pull a metal rod with a force about equal to what a doctor would use to check your reflexes in your knee.

As you can probably tell, I am on the beginner/amateur level so my terminology may not be the best. Essentially, I would like a small circuit device that can ring a bell every 30-60 seconds. Any help is greatly appreciated.

Calvin, JAMECO stocks the "actuators" you need.

Once you find an actuator, I or someone else here can design you a circuit.

Thanks for your reply. The basic version of what I am trying to do is make something for my wife. My wife meditates; she would like to hit a gong/chime every 30 seconds when she is in half-trance. If she is not meditating she would still like the chime to happen all day and night.

I may have over estimated my abilities in my previous post. I understand what these parts do, I just don't know how to determine what to use. I have worked with building circuits from schematics before, so I understand the process. But, engineering is beyond my capabilities.


However, the wife has been asking me to make this device for awhile now because she thinks I am "handy" with electronics because I ran a de-frag on her computer once.

Thanks

hi,
what you need is a timer using LM555 configured as an astable. its ouput is connected to the base of a transistor like a 2N2222A or a BC546 or a 2N3904. and connect your actuator to the collector side of the transistor and its emmiter to ground. if you need an schematic you can contact me thru my email. decide what specific time you need it to activate.

You might need something heftier than the transistors listed above. I would use a MOSFET, such as the IRF510 (Digi-Key p/n IRF510PBF-ND for around a buck). It will handle up to 5.6A (and more because of the low on-time and duty-cycle) -- but will work just fine for smaller loads all the way down to no load at all. Doing it this way removes a lot of the engineering uncertainty

yap, however due to limited infos, i would rather suggest a simple circuit.

That IS a simple circuit. And "yap" is the sound a dog makes.

Hey Steve,
Thanks for the reply. I had posted this same question in another forum also and one of the users there mentioned using a MOSFET transistor. They suggested 2N7000, or BS170, or VN10. Are they comparable? Are MOSFET transistors more "durable" in general? I would like the device to operate 24/7.

From what I have gathered, the power source will run to a LM555 timer, then to a MOSFET (possibly) transistor, then to my solenoid/electromagnet. Is that correct? What specs should I be looking for in a solenoid? Any suggestions?

This forum is great thanks guys!

The 2N7000 is for small power applications. I would have to look up the others (Google them for the datasheets).

A MOSFET is "durable" if you select the correct one for the application and protect it appropriately (e.g. snubbing rectifier across the solenoid/electromagnet coil).

Yup, LM555 drives a MOSFET with drives the solenoid/electromagnet. The "power source" will run to both the LM555 and the solonoid/MOSFET. Be sure to put a .1uF ceramic capacitor across the LM555 power pins (as described in the datasheet) and a 10nF from Vc to Ground (so noise from the solenoid doesn't feedback into the Voltage Control input and cause the 555 to trigger erratically (also described in the datasheet).

Here's an appnote on driving solenoids with FETs:

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slva460

Here's a great HexFET selection guide:

http://www.google.com/url?sa=t&rct=j&q=&esrc=...woCIDQ&usg=AFQjCNEJzwApWHSv0fkFyCeME8v35Lhcew

Can't help you with solenoid selection -- I'm not big on electromechanical.