Circuit Design Assistance

When motion-activated, the PIR sensor:

1. closes a pair of N.O. switch contacts,

2. opens a pair of N.C. switch contacts,

3. asserts +12V on an output lead/pin,

4. grounds an output lead/pin,

5. does something else (please specify)

How about just using this....

http://www.superbrightleds.com/moreinfo/switches/pir-motion-sensor-switch/831/

Raises an interesting point. That PIR sensor turns off ten seconds after motion *is no longer detected.*

To the OP: do you want an interval starting with the onset of motion and ending ten seconds later regardless of how long motion lasts, or do you want it to continue until ten seconds after the motion stops?

Note: in the latter case, if the PIR sensor detects the motion of the water, it may never shut the water off.

I have done some more research and have found a calculator that gives the on time for any given resistance and capacitance along with a circuit diagram.

Europium; you made an excellent point regarding the water causing a continuous on condition; as a result my initial plan has changed.

As of now the plan is to use the PIR to trigger two 555s. One will control a N Channel MOSFET holding forward bias to the gate for 10 seconds and keeping power applied to the relay activated valve. The other 555 will control a P channel MOSFET that will turn the power off to the PIR for 20 seconds.

Under continual motion this will give 10 second baths every 20 seconds while motion is being detected and avoid a continuous on condition.

I think this will be a fun project.

Thanks for your input.

Hi Gavilan,

Instead of two circuits, how about one configured as an oscillator with a 30-second period and 33% duty cycle? 10 seconds On, 20 seconds Off, with the oscillator powered when the PIR senses motion.

Btw, be sure to put a diode across the solenoid, diode's cathode to positive side, to protect your output transistor.

If you want to experiment and use two 555's why not use a '556' dual timer which will give you the 2 seperate timers in one package?

Thanks Cap - I saw that was available when doing my research. I have a slug of 555s on hand; otherwise I would.

Slight delay - tree fell on power line into my house and tore the meter out - 1 day delay. Boat went belly up - that's a priority issue. The PIR triggered water cannon will probably now have to wait until I return from my summer volunteer service in the mountains of Idaho.

Thanks for all your input everyone.

That looks EXACTLY like the PIR switch I am using.

If that is the same PIR that you have, note that it works only in darkness. But as squirrels are daytime critters .... ?

The PIRs I have are not night time only.

The LPIR-5A on that same site may be the better choice, as you can disable the nighttime-only feature. It does have a somewhat longer minimum timeout interval - 30 seconds - but features a +12V output which you can use to power a 555 oscillator directly, as mentioned previously.
http://www.superbrightleds.com/moreinfo/installation-supplies/intelligent-pir-motion-sensor-switch/969/

Why not use a microcontroller....Atmels 8 pin dip <$3 and you can trigger it and set up any delays or time functions you want.

I had considered a micro controller as I had recently been teaching myself how to program a parallax controller; but I want to learn more about 555 timers and I thought the simple circuitry I have envisioned might be a bit more robust in the environment.

I am going to check out Atmel 8 pin dip and see what I might learn - thanks !!

I just ran across a company in Co. 'sparkfun.com' check out their inventory, I ordered a pcDuino3 Saturday and it arrived yesterday and I plugged in keyboard, mouse, monitor and it booted, linked to my wifi and I am using it to do this fight now. Comes with operating sys(Ubuntu and android) Much better than Galileo from Intel which I'm still trying to burn Linux into a micro SD for. There is much information at 'instructables.com' on Arduino and programming the various Atmel chips.

Here is the circuit you need

You are a kind person. Thank You !!!

I will build and test it upon my return home in OCT.

"I will build and test it upon my return home in OCT."
Don't hurry. Is that 2015 or 2016???