I'm looking for a circuit that would utilitize a 555 or similar that will have 3 120VAC outputs that it alternates between. This would be used to drive 3 powerheads (water pumps) on a fish tank to create some wave motion in the water. I would think that the time it alternates could be varied based on a rheostat. Also, if possible, I want to have a pushbutton that would stop all 3 pumps for 30 minutes or so for feeding (push the button, power is killed for 30 minutes to the pumps, then they startup again automatically). So, probably would be 2 circuits. Anyone have a design for something like this or can help?
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.
555 -> 4017 -> 2N4401 -> relay coil. Set up the 4017 so the Q3 output resets it. Also, use one of the timer-counter chips, like a 4541, to inhibit the entire circuit using yet another relay for your 30 minute pause...
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
I was thinking of using the '10 minute timer' to power a second circuit consisting of the '555 timer tester'. Instead of powering the red LED in the timer circuit, I would have that power the tester circuit. In the tester circuit, I would substitute solid state relays for the LEDs. Is this feasible?
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.
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.