I want what I hope is a simple circuit but I've googled and searched this forum, not found it.

When a SPST digital programmable timer completes a circuit, I want one motor to run. On the next circuit completion from the timer the other motor. Next time, the first motor, and so on.

I can do this with two timers, each set on different times. But I would like to know if there is a simple way to do it with one timer.

Do NOT want a circuit that must be energized all day long. Over time that increases greatly the battery and solar requirements. Something like a latching relay? A bi stable flip flop maybe?

The application: A chicken coop door. Two water reservoirs. To open, fill the bottle on the door pulley. To close, pump from the door pulley bottle to the bottom reservoir. I can use an up timer and down timer but I think this can be done with some kind of latching relay or something.

The goal is to be very low-cost and simple. If the alternative to two timers costs more than the second $5 timer, I'll go with two timers.

  • \$\begingroup\$ better to use motor locked rotor current sense time delay to switch and latch off motor, with 2 FF's to store motor active state and toggle function \$\endgroup\$ Commented Oct 13, 2016 at 1:48
  • 1
    \$\begingroup\$ What voltage/current do the motors require? \$\endgroup\$ Commented Oct 13, 2016 at 2:51
  • \$\begingroup\$ These are very small water pumps. I just don't believe it would have any ability to do locked rotor current sense. * DC Voltage: 2.5-6V * Working current: 130-220mA * Power: 0.4-1.5W ebay.com/itm/… \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 10:46
  • \$\begingroup\$ Arduino is looking like an attractive alternative. I was initially intimidated by what I thought was high cost and complexity and difficulty to learn and fragility and high current usage; looks like none of these are a concern. There are 3.3V 4.7mA Pro Mini clones on eBay for $2 which can be switched into even lower power sleep mode. I know enough programming to figure it out and with the low cost/current, I can use two solar panel/battery/controller/pump setups for redundancy. If this becomes the solution I will provide the answer to my own question for posterity's sake. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 15:07
  • \$\begingroup\$ The timer is already energized, and whatever other circuit you’d need for the switching would consume less power than the timer – or at least it’d be easy to make it so. If you want it to be reliable, in spite of environmental conditions (chickens nearby will corrode most electronics in no time)– $5 will not even pay for the enclosure and necessary hardware, never mind the conformal coat spray, alcohol to clean it before coating, etc. Chickens are a price multiplier for sure. \$\endgroup\$ Commented Apr 27, 2022 at 19:55

3 Answers 3


A bi-stable relay would be fine, but you will need to be careful choosing one. Some are simple, some need very specific signals to toggle. Read the datasheets.

Aside: have you considered not using electronics?

Suppose the weight on the pulley was slowly leaking back into the lower container? Then you would power the pump to open the door, and it closes after some time by itself. This way you would only need one pump, a bit of aquarium tubing, and something to set the flow for the leak. Granted, you would need to pump more often.

  • \$\begingroup\$ I delight in simple solutions like that, but it would likely be very tricky to time a leakage juuuuuuuust right so it only closes 12 or so hours later. Would take lots of experimenting -- at 12 hours a time -- to get it right. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 10:49
  • \$\begingroup\$ Further complicating the matter I want there to be a second door opening ten seconds after it's closed for latecomers, as seen on a more expensive door closer product. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 12:36

You need circuit, that has two parts:
1. H bridge to be able run motor in both directions. I will not go to details about that, Mr. Google knows all about it, just ask him.
2. "Button with memory"

You have timer, which closes circuit, just like a button. I'm a simple person, I like simple things, I will speak like it is a button.
You need different initial conditions when this button is pressed. In fact you have different conditions alredy, you just need to take advantage of it. One condition is with doors closed, the other with doors open.

I would suggest using relays to implement it. To detect initial condition, there are many possibilities, one of them is magnet and reed relay. Place magnet on the top of doors and place reed relay in position, that matches with magnet when doors are open, or closed, whichever fits you better.
You need two additional relays to remember initial condition after doors will start moving and that's it. You have signal direction signal, which you will use as input for H bridge.

  • \$\begingroup\$ I initially didn't want to put reed switches on the doors -- two reservoirs being elegant enough not to fiddle with switches and door positions. But given I would have needed two timers to implement, that's ugly. I am thinking two reed switches and a motor reversing latching relay is going to be the way to go. Raise the door, hit the first switch, kill motor and reverse polarity for next time. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 10:53
  • \$\begingroup\$ So a reed switch to kill the motor and a latching DPDT push switch to reverse current. They'd need to be lined up very well to actuate at the same instant. (One reason I didn't want to fuss with them.) Though the momentum of the door after killing the power should still actuate the reversing switch even after power is gone, so that's good. So they wouldn't need to be perfect, just very close. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 11:23
  • \$\begingroup\$ I'm confused. Not a reverse current switch but a switch to choose the 2nd circuit. \$\endgroup\$
    – SlowBro
    Commented Oct 13, 2016 at 13:05
  • \$\begingroup\$ I misunderstood you a bit. You have 2 pumps for 2 directions, not one motor, that should have 2 directions. In that case, you don't need H-bridge, you just need a simple circuit with reed relay. I see... you need also to detect when to stop pump. In that case, 2 reed relays will be needed. \$\endgroup\$
    – Viliam
    Commented Oct 17, 2016 at 6:05

Going to try an ESP8266, which is similar to an Arduino but with Wifi. As mentioned in the comments, I was initially intimidated by what I thought was high cost and complexity and difficulty to learn and fragility and high current usage; looks like none of these are a concern. The ESP-07S uses 0.9mA in light sleep mode, costs $3, and is fairly straightforward to program. With the low cost and current, I can use two solar panel/battery/controller/pump setups for redundancy.

Thanks everyone.


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