sprinkler one shot timer

Well, you HAVE that.

What you're doing is *not dealing with THE PROBLEM*.

If *motion* AFTER shutdown is the problem, you need a **deadband** where you disable the trigger until things are still again. This requires a *second* timer which trips at the OFF point of the first.

Try putting the sensor out of view of the water...

Very true on both fronts I realize it needs a timer to turn the water on then another way of turning the water off for 30 seconds or so. I'm stimyed as to how though. I did tell him to try a different lens on the MS like sunglasses or aiming it different I'll have him try that first before I build a 556 timer board if he feels it is that important Again for your time and expertize I am truly grateful I'll be back. Wayne

Use a Timer relay with 2 sets of contacts for the trip cycle. A delay off type would be good. One set of contacts will lock it on, and the other set of contacts will disable the sensor. Many timer relays will reset it's timer if the input retriggers and thus it may not expire. And for the sensor, you should have a time on delay power source that was interrupted from the first timer to disable it. The reason for this is, when the main timer expires and turns it self off. This would then reconnect the sensor. If water is still in the air, you'll get a false start. Using a delay on timer for a power source to run the sensor will fix that. SO basically, first timer is a Delay OFF type using one set of it's own contacts lock on the input signal. the other set of contacts will disconnect the power to the Time on delay relay for the sensor.. When first relay expires. it'll turn on the delay on relay for the sensor. mean while, water in the air should be clearing. when the delay on sensor expires., the contacts will then close to allow sensor activity once again.

You can actually do all of this with a 556 timer, (dual 555). the first timer will be the delay on for the sensor, the Reset line of this timer will be controlled from the output side of the second timer etc...

Simple. What you really need to do is keep the motion sensor from being set off by the water from the sprinkler system. Use a relay to interrupt power to the sensor, or output from the sensor, when the sprinkler is on. The drop out of the relay is delayed by a capacitor, so the water will finish falling befor the sensor is turnde back on.

The relay will be driven by a transistor, which will be held in the on state for a few seconds after the sprinkler turns off. I'll draw an NPN circuit as an example, which takes a plus 12 from the sprinkler when the sprinkler is on, to turn the relay on. (When the relay is on, the sensor is interrupted.)

• 12 ----------+---[Rly]---+ | | +-----|---+---[1K]---+-----| NPN | | \e [10K] [470uF] | | | | Gnd ----+----------+-------+

In effect, the transistor amplifies the capacitance, delaying the dropout *much* longer than if you simply placed the cap in parallel with the relay coil. The delay will depend on the transistor gain and relay coil resistance, but should be a few seconds. You can change that to a few minutes, if you want, by using a darlington transistor and increasing the 10K to 1meg, or make it variable by using a 1meg pot with the darlington.

Ed

Sorry to interrupt. May I know what is indicated by that symbol just below the relay (Rly) in the circuit diagram shown

Diode

ahh yes.exactly.thanks