# Looking for simple 555 relay circuit

Discussion in 'Electronic Basics' started by ZhangLu, May 24, 2004.

1. ### ZhangLuGuest

Hi all,

Looking for a circuit diagram (on trip board) that utilizes ic 555, using
12V AC power input that:

On when pressing a switch
Off when pressing the same switch
Beeps every 10 sec.
Drives a 12V 55W light (AC or DC)

Can anyone help?

Regards,
New learner

2. ### JeffMGuest

New learner (ZhangLu) asks:
Easy so far.
Not a problem.
How long does it beep?
Be much more specific: When does it light; when does it go dark?

In the future, basic questions should remain in sci.electronics.basics.

3. ### Terry PinnellGuest

My guess would be say 500mS. So an astable with appropriate duty cycle
would drive it. And it could be gated by a flip-flop, triggered by
momentary switch contact.

But what device is to be used for the beep? A DC buzzer? If it's a
miniature loudspeaker, a further circuit section is needed to provide
the oscillator. At what frequency?
Fair point - I suppose I'd have assumed it would light simultaneously
with the beep. IOW, a Beep & Flash alarm of some sort. But it would be
good not to have to guess <g>.

How important is it that it to use a 555? At first sight I'd have
thought it easier to implement with CMOS 4001/4011. The light
requirement means a relay is needed anyway, so one major merit of 555
- its 200mA direct output drive current - is of no consequence. And
although you can make a F/F (bistable, or 'toggle') with a 555, it's
more usual to use a couple of logic gates.

BTW, I take it this is not homework?

4. ### ZhangLuGuest

The bulb will light on when the switch is pressed once, and the DC bleeper
will beep every 10 sec simultaneously as a 10 sec counter until the same
switch is pressed again to stop both the light and bleeper.

5. ### ZhangLuGuest

Thanks Terry.

I'm a new hobbyist trying to play with 555. If you think CMOS 4001/4011 can
do the trick better, are you able to suggest a circuit for me to work on?
TQ.

6. ### SoerenGuest

Hi Terry,

I assume from this:
"On when pressing a switch
Off when pressing the same switch"

That the lamp should be considered the output (on = light and vv.)

The next part: "Beeps every 10 sec." I see as something independant of
the switching ?

Something _similar_ to a manualy controlled photographic enlarger with
beeps to mentally count off the interval at hand ?

7. ### Terry PinnellGuest

By 'switch', I assume you mean a momentary contact push-button? As I
said earlier, that will require a simple flip/flop (toggle) followed
by a gated astable.

But must you use a push-button? If you used a simple SPST switch
instead, then you could eliminate the toggle. You would switch control
directly to the lamp circuit, and off again (a relay, switching higher
power to the lamp). And that same signal would gate the astable, which
would drive the DC beeper.

If it *does* have to be a push-button, please confirm that this is the
intended timing diagram.
http://www.terrypin.dial.pipex.com/Images/LightBeeper.gif

8. ### ZhangLuGuest

G'day Terry,

Thanks for the diagram, that's exactly the timing I intended to have. The
switch is a momentary contact push-button.

ZhangLu
New Learner, Malaysia

9. ### SoerenGuest

Hi ZhangLu,

Thought so But what precision do you need in the timing of the 10
second intervals ?

If demands are not too strict on timing, it could be build with...
1 CD4093, 3 transistors, a couple of diodes, a few caps, ~12 resistors, a
small (32 Ohm?) speaker, a relay and the pushbutton.

--
Regards,
Soeren

* If it puzzles you dear... Reverse engineer *
New forum: <URL:http://www.ElektronikTeknolog.dk/cgi-bin/SPEED/>

10. ### Terry PinnellGuest

OK, here's a circuit to do it. It contains full notes, so should be
self-explanatory, but post again if not clear. Breadboarded and works
fine.
http://www.terrypin.dial.pipex.com/Images/LightBeeper-ZhangLu.gif

Many alternative designs are possible. And you could use a relay for
driving the high power lamp if you have a suitable one to hand,
instead of the power MOSFET I've recommended.

11. ### Terry PinnellGuest

Far fewer than that <g>. See
http://www.terrypin.dial.pipex.com/Images/LightBeeper-ZhangLu.gif

What were you proposing to use around 12 resistors for?

12. ### Terry PinnellGuest

[etc]

One point I forgot to mention. C2 must not be a polarised type. In
this case I connected a pair of identical 10uF electrolytics in
series, back to back (-ve ends together). That effectively gives a 5uF
non-polarised equivalent.

| + ---
### 10uF |
--- |
| |
| | = 5uF
--- |
### 10uF |
| + |
|

13. ### SoerenGuest

Hi Terry,

Well, that _won't_ work, so you get a (free) extra try

Making it work (with bipolars, including one used as inverter), with
10 sec. period adjustable +/- ~2.5sec and generator for the beep sound
into a speaker.

<URL:http://www.ElektronikTeknolog.dk/Circuits/PB-ON-OFF_w_beeper.gif>

--
Regards,
Soeren

* If it puzzles you dear... Reverse engineer *
New forum: <URL:http://www.ElektronikTeknolog.dk/cgi-bin/SPEED/>

15. ### ZhangLuGuest

Thanks everybody!! I've learned a lot from all of you.

BTW Terry, may I assume that this circuit works on 12V DC and the
+ve input is around C3?

I intend to use a heavy duty relay to replace Q1 MOSFET to drive the 55W
lamp.

Again, thank you so much.

Regards,
ZhangLu, New Learner
Malaysia

16. ### Terry PinnellGuest

As I said, "Breadboarded and works fine." Would you like to see a
screenshot of its output? And it simulated OK too. There's always the
possibility that I've drawn a different circuit to the one I simulated
and built, but at a quick check that doesn't appear to be the case.
What are your problems with it?

17. ### Terry PinnellGuest

Agreed, but I hardly think that matters in this application, do you?
One press of the button, if necessary, if he wants to 'start' with
light and beeping OFF.
Ah - I now see I *have* drawn it incorrectly, sorry! U2Cpin8, C2, R3
and D1 share a common node, but do *not* go to Vdd, as you rightly
point out, thanks.

18. ### Terry PinnellGuest

Obviously *too* quick! Fred's post prompted a closer look and I've now
corrected that silly drawing error. Any more problems with this
working circuit?

19. ### Terry PinnellGuest

Yes, it works fine at 12V. I assume you have the corrected schematic?
http://www.terrypin.dial.pipex.com/Images/LightBeeper-ZhangLu.gif

Pins 14 and 7 of the 4011 (or 4093) go to 12V an 0V respectively.

OK. Instead of wiring to the gate of MOSFET Q1, use a simple relay
driving section like that in Soeren's circuit.

20. ### SoerenGuest

Hi Terry,

Yup

I guess you are one of the build-first-make-drawings-later kind of guys ?
Even if you are, build after the schematic when it is finished, or better,
let somebody else build it up, it will catch all these drawn-late-in-the-
night errors

Not except that you cannot adjust the timing and you have to use a buzzer
instead of a cheaper "loose" piezo disk

(Just teasing you know

--
Regards,
Soeren

* If it puzzles you dear... Reverse engineer *
New forum: <URL:http://www.ElektronikTeknolog.dk/cgi-bin/SPEED/>