looking for a 555 timer circuit

Although the guys for whom solder is a favorite programming language may have different ideas, I'd do this with a small microcontroller. One A/D port to read the rheostat, a digital port to sense the pushbutton, and three digital outputs to control the power to the pumps.

Could probably be done with an 8-pin ATtiny15 (same size as the 555) which has an internal oscillator, a couple of timers, and four A/D channels plus the rheostat, pushbutton, relay drivers, and relays.

I'm looking for the solder version :^) I have most of the parts on hand to build this, just not the knowledge of where to put the parts.

Take a look at the "555 Designer" at:

The datasheets for these chips and transistors are freely available, and usually have application schematics in them that are close to what you are interested in. If you need more help, post again.

Note that you'll need a DC supply for the logic, which won't run on AC.

Would something like this work: I'm looking at the samples shown on

Assuming so: The timer circuit isn't exactly what I want, but close. Can someone show me what to change to make it 'default' to power on (across the red LED), and how do I calculate what value of resistor to use in place of the 500k resistor to get approximately 30 minutes of no power across the red LED?

In the tester circuit, if I substitue a pot for R2, would this allow me to adjust how long the relays would be powered? I would want equal times (or as close as possible) of about 30 seconds on and 30 seconds off. Ideally, I would want 3 outputs instead of 2, but this is a start.

Hope this makes sense, and thanks for any help anyone can offer.

Why? Fish can't eat when there are waves?

--DF

haha. They can, but corals and some slower moving fish/creatures in saltwater environments need more time to catch food before it's filtered out.

An alternate approach that might turn out to be easier if you persist in your perverse dislike of microcontrollers (insert smilies here as required to assist any humor-impaired readers) is to drop back to an older method of implementing long period timers: motors, gears (or belts), and a cam shaft. Think of a music box or washing machine timer.

There would still be a 555 but this time (no pun intended) as a PWM generator that controls the speed of a small DC motor. The motor, through suitable gearing, turns a cylinder through one complete rotation every "wave cycle." High spots on the cylinder press against microswitches that in turn actuate the relays that handle the high current needed for the main water pumps. Fine tune the rotation period with a standard 555 PWM circuit.

The half-hour feeder timer could be a similar gizmo. Turn it to the starting position that shuts a microswitch controlling a double throw relay. The NO position of that relay would run another motor (and 555 tuner if required) until it reaches the low spot which opens the microswitch, opens the relay, and stops the motor. The NC position would be in the power path for the water pumps. While it's open, the pumps are off. When the half-hour relay drops out, those contacts shut again and the pumps start up.

With the cam setup, it would also be pretty easy to cut more complex wave profiles with, e.g., more dwell time for the pumps on either end of the tank than the one in the middle, simulating (roughly) simple harmonic motion that "sticks" more at the extremes and moves more quickly through the center.

John,

No, you are correct. What I want is what you show in the first timing sequence.

--- OK, it's on alt.binaries.schematics.electronic under "Looking for a

The outputs are positive true and should be able to drive a solid-state relay each.

-- John Fields Professional Circuit Designer

John,

Thank you. I'll build this over the weekend and let you know how it works!

--- You're welcome. :-)

Just as an aside, you can use a 4020 or a 4024 instead of the 4060 that's on the drawing, as well as the HCMOS (74HC40XX) versions (preferred) if you happen to have them around.

If you get into trouble and you need to do some troubleshooting to bring it to life, here's how it's supposed to work:

U1 is a 7555 (CMOS 555) wired as a free-running 50% duty cycle astable multivibrator, and it supplies clocks to U2 and U4 all the time.

Pressing S1 momentarily will RESET U4 and the RS latch, U3B-U3C, forcing u2-1 low, which will keep the outputs of U2 low (and the motor driving relays inactive) until U4 times out.

U4 times out after counting 64 low-going clock edges, and when it does, U4-4 goes high, SETting the RS latch and forcing U2-1 high.

U3A is a 2-input NOR gate, and since U2-2 and U2-7 are being forced low while U2-1 is low, U3-1 and U2-4 will be forced high until the first high-going edge of the clock gets to U2-9 after the latch is SET by U4 timing out.

When that clock pulse gets to U2 it shifts the high on U2-4 to U2-2, enabling OUTPUT1 _and_, forcing U3-1 low. U3-1 going low will cause U2-2 to go low and U2-7 to go high after the next high-ging edge of the clock. Since U2-7 will now be high, U3-1 will stay low, and the next clock will make U3-2 low, U3-7 low, and U3-10 high,

Now, since U3-3 and U3-2 are both low, U3-1 will be high and the three-phase cycle will begin anew with the next clock:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ CLK _| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_ _____________________________________________________ U2-1 __| ___ ___ ___ ___ ___ U2-2 ____| |_______| |_______| |_______| |_______| ___ ___ ___ ___ U2-7 ________| |_______| |_______| |_______| |_______ ___ ___ ___ ___ U2-10____________| |_______| |_______| |_______| |___

Finally, since you said you wanted about a 30 second 'ON' time for each motor when the thing is operating and about a 30 minute pause when you hit the PAUSE switch, that means there will be 1800 seconds in each pause period and 30 seconds in each active period.

If we make the period of the clock 30 seconds, then the total number of clocks we'll have to count up to get the 30 minute pause will be

Which is pretty close to what U4 counts up to, 64, so if you use the pot to adjust the motor ON times to 30 seconds, the pause time will be:

t = 30s * 64 = 1920s = 32 minutes.

Not bad.

-- John Fields Professional Circuit Designer

--- Aarghhh!!!

I just saw how to get rid of the 7555.

Use S1 to RESET the 4060 and the rest of the circuit, and then when S1 is released, use the 4060's front end for the oscillator it's supposed to be. Then use its LSB to drive the '175 and use its Q9 to drive the latch. Or something like that. I'll work it out and post the new schematic tomorrow.

-- John Fields Professional Circuit Designer

John,

Is C1 100 F, or should it be 100 uF?

---

-- John Fields Professional Circuit Designer

Ok, I'm holding...

Got the update. RevB is much cleaner. Thank you for doing this.

--- You're welcome. :-)

In going over the circuit for the last time, (LOL) I found a few errors:

1. U2-5 should be connected to U1-3, not U1-1
2. C1 should be an 0.18µF polyester cap.
3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film resistor.

-- John Fields Professional Circuit Designer