# Timed on/off switch

Discussion in 'Electronic Basics' started by [email protected], Mar 22, 2007.

1. ### Guest

Hi, this is my first post here, and I looking for either a component
or a circuit design for a special project I am doing.

Basically I need a component that switches the current running through
it on and off at a frequency of about 1-6 Hz.

I am fairly apt at soldering a general circuitry so any suggestions
would be great!

Thanks,
-KV

2. ### Greg NeillGuest

AC or DC current?
How much current?
What voltage?
What is your power supply voltage?

3. ### Guest

It will be a DC system running at 12V. It will be carrying close to 3
amps at max. It will be getting the power from a AC-DC converter
plugged into the wall. The load will be a electromagnet.

4. ### Homer J SimpsonGuest

What purpose is there in cycling such a magnet at 6 Hz?

5. ### Guest

Well, I guess that 6 is a little high... maybe around 2 Hz will be
optimal. I am trying to make my own unique design for a tattoo gun I
am making.

8. ### John FieldsGuest

---
View in Courier:

..+12>--+--------------------------+--------------------+
.. | | |
.. | | +-------+
.. [1000] +---------+ | |K |
.. | 7|_ |8 | [DIODE] [COIL]
.. +------------O|D Vcc|--+ | |
.. | 6| _|4 | +-------+
.. [82K] +-----+--|TH R|O-+ IRL3303 |
.. | | | 2|__ |3 | \ C
.. +->[500K] +-O|TR OUT|--|-------------+----B
.. | | | GND | | |K E
.. +----+ +----+----+ +------+ | |
.. | 1| 555 |+ | [1N4744] |
.. [0.68µF] | [10µF][100nF] | |
.. | | | | | |
..GND>-------+-------------+-------+------+------+------+

The 10µF electrolytic and 100nF ceramic capacitors are to be mounted
directly across pins 1 and 8 of the timer.

The 0.68µF capacitor is polyester film (Mylar).

With the 500k rheostat at minimum resistance the output frequency
will be about 6Hz and at maximum resistance the output frequency

9. ### Guest

Wow, thanks guys!

10. ### Homer J SimpsonGuest

Look at HowStuffWorks.com and search for the buzzer demo. That's basically
how to do this.

11. ### Rich GriseGuest

Yes, it's called a transistor. But I'd put it in the negative lead
(your white one), and call the negative output of the supply "ground";
it makes the control circuitry simpler to design, because then it can
all be referenced to ground.

You need something to generate the pulses, like a 555 or astable
multivibrator, and the output of that will switch the transistor on
and off. You'll also need a "catch" diode, which is a diode in
parallel with the coil, that absorbs the inductive spike when
the current is turned off. Some might recommend a MOSFET - for
something on this order of complexity (which isn't very much,
for an old fart, albeit for a newbie it can be daunting), it's pretty
much a matter of personal taste.

Do you have any electronics experience at all? If not, I'd recommend
searching the web for tutorials and such so you have a handle on what
you're trying to accomplish, and how to go about doing it.

Good Luck!
Rich

13. ### Guest

This whole thread has been a great help! As for my electronics
background... I am a level 2 electrician apprentice... Although this
doesn't help much as far as experience on low voltage DC systems, I
understand everything that has been discussed here and have a good
grasp on electrical flow and I can solder well.

Now one thing I am unclear about (this may sound like a stupid
question)... If I am looking at an electrical circuit diagram and it
leads a few parts to the ground symbol... do I just connect it to the
box I'll be putting it all in?

14. ### Rich GriseGuest

Only if the box is metal.

And, one of the conventions in sci.electronics.basics is that there is
no such thing as a stupid question, unless you ask the same one three or
four or five or ten times, trying to get the answer you think you want
instead of the right one (of which there are usually several).

If you really want to set the world on fire, invent a tattoo eraser
that's as cheap to have done as having the tattoo installed in the first
place.

Have Fun!
Rich

15. ### Homer J SimpsonGuest

You can generally find the US Army or Navy instruction books online. They
are a very good starting point for learning since they have been used many
many times for teaching these subjects.
You can. Or you can just connect all of the ground connections together. The
notion of ground is a conceptual one - it really means common return to the
power supply, sometimes with an element of shielding associated with it.

16. ### Guest

Okay... I think I found the circuit I am going to try to assemble... I
am confident that I can do it:

http://www.tkk.fi/Misc/Electronics/circuits/strobocontrol.html

But the load of course won't be a light, rather an electromagnet...
and I will connect a MOSFET in parallel with the electromagnet to
avoid the damages of any current spikes. What do you guys think?

As for a tattoo eraser... I'll worry about building one of those when
I start having kids

Thanks!
-KV

17. ### Homer J SimpsonGuest

Be aware that the coil / stylus assembly will have a mechanical resonance of
some sort. Syncing your driver to this will be less than fun.

That's why most every unit you can find just uses a set of point which break
the current at max forward position.

18. ### Guest

Another thing I might just want to throw out there is that I am also
looking for other ways of preforming this operation. Basically what I
want to happen is:

http://i83.photobucket.com/albums/j306/krelver/tattoogun.jpg

1. Electromagnet energizes
2. Electromagnet attracts permanent magnet
3. Electromagnet denergizes
3. Permanent magnet get pushed away by the spring

And all off this to repeat at about 1-3hz...

Using a 555 timer in a strobe light circuit is the best I can think of
at the moment.

I am also using this project to gain experience in the electronics
field.

All of your suggestions so far have been great!
-KV

19. ### ehsjrGuest

Something like this should do it for you:

+12 ---+------------------------------------+
|a |
[D1] |
| |
+----+--------+---+ |
| | | | +----+
| [1K] --------- | |
| | | 8 4 | | |
| +-----|7 | [100K] |
| | | | | |
| [33K] | 555 | | |-+s
| | | 3|---[330R]-+-,| STP12PF06
| +-----|6 | g||-+d
[100uF] | | | |
| +-----|2 | +----------+
| | | 5 1 | | |
| |+ --------- | |
| [10uF] | | [Electromagnet] [D2]
| | [.1uF] | | |a
| | | | | |
Gnd ---+----+--------+---+------------------+----------+

D1, D2 = 1N5404

With the values shown, the 555 should give you about
2 seconds on, 2 seconds off. Use a regular NE555, not
the cmos TLC555 version.

Ed

20. ### Guest

Thanks Ed, that actually looks a lot simpler than the one I planned on
using (and a bit more applicable)... A few questions: What type of
diodes should I use? and what components should I change if I wanted
to increase the frequency slightly? Could I add a rheostat anywhere?
2s on and 2s is a bit too slow, I think.