# Delay Circuit for PIR Motion Sensor

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#### ingalfsan

##### New Member
Hello dear friends.

I need your valuable help for a little circuit I'm designing.

It is a small circuit to incorporate a delay to a PIR motion sensor that activates a spray that releases compressed air to drive away birds, cats, dogs etc. The detail is that once the sensor is activated, it will be inactive for 5 or 10 minutes (this will prevent it from being retriggered during that time). For space reasons (the PCB must have 2 "x 1.5") I have been trying to do it using only BC547 transistors. Anyway, a circuit with a classic NE555 would also serve me!

The PIR I'm using is a naked PIR without a stabilization circuit. Any ideas are welcome!

The circuit I have done so far uses a darlington array and keeps me on a led for about 30 seconds after activating the switch (which is supposed to act as a PIR sensor). I really do not have a clue where to start. I have done several circuits with NE555 in astable and monostable mode, but that if I keep an active circuit for a second and inactive for 5 minutes I have no idea how to do it. I have a lot of experience programming Arduino, PIC, Raspberry, IoT applications (I am at your command), but some basic electronics issues surpass me.

Thank you very much in advance.

Attached images and Proteus files of what I have done so far.

#### Attachments

• PIR Spray.zip
24 KB · Views: 50
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#### MikeMl

##### Well-Known Member
Welcome.

Is the PIR sensor like this one? If not, post a link to the one you are actually using.

What is the actuator for the air spray? Solenoid? Operating voltage? Current?

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#### cowboybob

##### Well-Known Member
... The detail is that once the sensor is activated, it will be inactive for 5 or 10 minutes (this will prevent it from being retriggered during that time). ...

So you want the PIR signal to trigger, in order:

1. the noise maker.
2. a circuit to disable input from the PIR for 5 to 10 minutes
3. at then end of 2. above, re-enable input from the PIR to restart from 1. above.

Is that correct?

Also, it's useful to note that the output of PIRs generally goes HIGH on power up for ≈5S, as they equilibrate the infrared field. This action generally has to be squelched or otherwise removed/disabled to avoid an unwanted activation of any following circuitry. Is that going to be a problem for you? If it is, it will somewhat complicate the circuit I have in mind .

Note also that when triggered, the PIR output will stay HIGH for ≈5S.

#### ingalfsan

##### New Member
Hi!

Welcome.

Is the PIR sensor like this one? If not, post a link to the one you are actually using.

What is the actuator for the air spray? Solenoid? Operating voltage? Current?

The PIR sensor I am using is like the figure.

I have one with stabilization circuit (Identical to the one shown by you), but my client does not :-(

The actuator is a kind of relay.

#### ingalfsan

##### New Member
So you want the PIR signal to trigger, in order:

1. the noise maker.
2. a circuit to disable input from the PIR for 5 to 10 minutes
3. at then end of 2. above, re-enable input from the PIR to restart from 1. above.

Is that correct?

Also, it's useful to note that the output of PIRs generally goes HIGH on power up for ≈5S, as they equilibrate the infrared field. This action generally has to be squelched or otherwise removed/disabled to avoid an unwanted activation of any following circuitry. Is that going to be a problem for you? If it is, it will somewhat complicate the circuit I have in mind .

Note also that when triggered, the PIR output will stay HIGH for ≈5S.

Hello!

That's exactly what I want. The PIR input (or the circuit output that activates the spray) should remain inactive for about 3 to 5 minutes before reacting to the PIR again.

Certainly the sensor while stabilizing stays HIGH for about 5 seconds. That would be no problem. I could devise a small stabilizing circuit for that.

What circuit do you have in mind?

#### MikeMl

##### Well-Known Member
...
I have one with stabilization circuit (Identical to the one shown by you), but my client does not :-(

The actuator is a kind of relay.
So we still need to know what voltage it operates from, and how much current it needs.

So you are being hired as a consultant, doing work for pay, and you expect us to hand you a solution that you get paid for?

#### ingalfsan

##### New Member
So we still need to know what voltage it operates from, and how much current it needs.

So you are being hired as a consultant, doing work for pay, and you expect us to hand you a solution that you get paid for?

Hi!

Nop, the circuit is actually for a client who was charged for an Arduino prototype for climate monitoring. It's actually a favor he asked me because the animals come to the greenhouse and they mess up the plants. I did not charge him because I thought it was a simple thing, but suddenly it got complicated. In fact I have a similar circuit that works perfectly, programmed in PIC 12F675, but the client that I mention does not reside in my country, and does not have a PIC programmer at hand. The voltage is 9V, by the way.

#### ingalfsan

##### New Member
A friend has facilitated this circuit to me.

It works this way:

When the LCD screen turns off, turn off the lamp as well, and keep the power on for about 5 minutes so that the fans continue to run. This will cool the cabinet by removing all the residual heat from the lamp. He have been walking it for several years and it has never failed.

The timer part consists of Q2, Q3, the r of 47k and the capacitor of 1000uF, the diodes are to avoid voltages in other parts of the circuit.

I don't know if it could serve to you who has more experience with hard electronics.

#### ingalfsan

##### New Member
Hi!

I have tried my circuit in Proteus and in a small protoboard. The PIR appears mounted on the photo, but before testing I disconnected it. I want to test the delay circuit first, because the PIR needs a little stabilization circuit, so that at the moment of feeding it does not interpret the 5 second HIGH as there is an animal nearby, as CowboyBob saids That is another problem that I must solve later.

Then, I changed later the resistance of 2.7K by 47K and now the led takes about 18 seconds ON. It is gradually getting closer to the result. I have thought that if I put something like a transistor on the output as a negator, I can do that instead of turning it ON, it will be OFF for that time.

Will I be on the right path?

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#### cowboybob

##### Well-Known Member
Unfortunately, I only understand English. So I can't exactly fully understand your attached schematic .

Could you post the exact schematic that you used to populate the protoboard (including inputs and outputs)? Especially this part:
...some sort of SMPS? And what is its purpose?

And I unsure what the PIR is exhibiting such that it requires a "little stabilization circuit". And on that note, the PIR's "bare bones" (i.e., no enclosure to limit its "window") condition is likely to exhibit repeated false positives that will have your noise maker firing off to excess (perhaps this is the reason you need the stabilization circuit??). I've seen unfocused PIRs respond to a momentary change in the air temperature in front of an unrestricted field of view.

#### ingalfsan

##### New Member
Unfortunately, I only understand English. So I can't exactly fully understand your attached schematic .
View attachment 106192...some sort of SMPS? And what is its purpose?

Yes. That part is the power connector of an ATX motherboard, from a switched-mode power supply. Actually my friend passed me that circuit to show me this part, which is exactly like my circuit, only that it is mirrored.

Could you post the exact schematic that you used to populate the protoboard (including inputs and outputs)?

That's my circuit. The PIR appears mounted on the proto, but It's disconnected. I only managed to keep the led on for about 18 seconds after disconnecting the battery.

And I unsure what the PIR is exhibiting such that it requires a "little stabilization circuit". And on that note, the PIR's "bare bones" (i.e., no enclosure to limit its "window") condition is likely to exhibit repeated false positives that will have your noise maker firing off to excess (perhaps this is the reason you need the stabilization circuit??). I've seen unfocused PIRs respond to a momentary change in the air temperature in front of an unrestricted field of view.

Very interesting. I certainly have to put a Fresnel lens to the PIR to avoid false positives. Truthfully, I've never tried a PIR sensor without that little coverage.

In fact, when I referred to a naked PIR I meant that it does not have the stabilization circuit that has an HC-SR01, for example, with trimmers to adjust time and sensitivity.

I've never actually used a PIR alone. Do you have any idea for this?

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#### cowboybob

##### Well-Known Member
Yes. That part is the power connector of an ATX motherboard, from a switched-mode power supply. Actually my friend passed me that circuit to show me this part, which is exactly like my circuit, only that it is mirrored.
Thank you. I should have paid more attention to the pinout #s.
That's my circuit. The PIR appears mounted on the proto, but It's disconnected. I only managed to keep the led on for about 18 seconds after disconnecting the battery.
Well, to achieve the delay period you're suggesting (5 or 10 minutes), the only reasonable, simple analog circuit will have to use at least 2 555 timers, which will, of course, have to be powered for, at the least, the duration of the delay plus a few seconds.
I've never actually used a PIR alone. Do you have any idea for this?
No. I'd strongly suggest you get a PIR like this one: All you have to deal with is mounting and focusing (if it needs focusing).
A suggested circuit:

Suggested relay.

#### ingalfsan

##### New Member
Someone asked me how it could be solved using code. The code for ATTiny or Arduino is something like this:

Code:
#define TRIGGER_TIME  (1000L)  // 1 sec
#define IDLE_TIME (5*60*1000L)  // 5 mins

SimpleTimer timer;

boolean PIRActivated= 1;

void PIRcheck() {
if (PIRActivated == 1) {
// Here goes the code for activate relay etc
PIRActivated=0;
timer.setTimeout(IDLE_TIME, activatePIR);
}
}

void activatePIR() {
PIRActivated=1;
}

void setup()
{
timer.setInterval(TRIGGER_TIME, PIRcheck);
}

void loop()
{
timer.run();
}
[/QUOTE]

#### ingalfsan

##### New Member
Hi!

Thanks to the excellent advice from all of you, in particular from cowboybob and MikeMl, I have achieved what I needed. I have a timer that activates a led for about 0.69 seconds and another led every 1.15 minutes, using a 1N4148 diode between pin 7 and pin 6. Actually, what I want to do is to activate a device to scare animals, which I do not want to be retriggered for 1 minute.

The timer works fine, but I have not been able to activate it with the PIR motion sensor. The cycle should be activated every time the PIR is triggered, and then wait for 1 minute, but I can not make it run correctly with the PIR. Each time the PIR is activated, the cycle starts again instead of waiting for one minute.

Any suggestions?

#### cowboybob

##### Well-Known Member
My previous circuit was inadequate. My apologies.

Circuit below is part of a considerably more complex design that is currently working in a commercial application that responds to a "presence" by playing an MP3 file. It ignores any additional PIR signals until the MP3 file terminates (at which point a different MP3 file is cued and then plays with the next PIR pulse):

Current values of both pots and C1/C2 allow Noise Maker Controller trigger timing from 0 to 1.1 seconds and PIR Disable timer from 0 to 110 seconds. Change C1 and/or C2 to alter timing as needed. You can, of course, replace the pots with resistors of your choice.

I should note that the relay was the best, easiest and most reliable solution for providing the interruption of unwanted PIR signal(s). If you can find a 9VDC NC SPST relay, feel free to use it instead of the SPDT shown (which I used in the circuit referenced above).

<EDIT> Left out D1 - relay kick-back snubber. Also, the five second duration noted in point 1. of the sequence listing is a typical PIR device's pulse duration, not how long I held down the POS switch button.

Last edited:

#### ingalfsan

##### New Member
My previous circuit was inadequate. My apologies.

Circuit below is part of a considerably more complex design that is currently working in a commercial application that responds to a "presence" by playing an MP3 file. It ignores any additional PIR signals until the MP3 file terminates (at which point a different MP3 file is cued and then plays with the next PIR pulse):
View attachment 106606
Current values of both pots and C1/C2 allow Noise Maker Controller trigger timing from 0 to 1.1 seconds and PIR Disable timer from 0 to 110 seconds. Change C1 and/or C2 to alter timing as needed. You can, of course, replace the pots with resistors of your choice.

I should note that the relay was the best, easiest and most reliable solution for providing the interruption of unwanted PIR signal(s). If you can find a 9VDC NC SPST relay, feel free to use it instead of the SPDT shown (which I used in the circuit referenced above).

<EDIT> Left out D1 - relay kick-back snubber. Also, the five second duration noted in point 1. of the sequence listing is a typical PIR device's pulse duration, not how long I held down the POS switch button.

Excellent! It looks great. Surprising design.

Now I'll try something like this. I will keep you informed of my progress.

Thank you!

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