Using a motion sensor to start a small motor.

Thread Starter

marshallh

Joined Mar 7, 2018
4
I am building a motion sensor activated cat toy so my cat will spend a little less time annoying me. I have a PIR motion sensor. 5v-12v to power the sensor. The output however is only 3.3v. I have a 9v battery powering the sensor but the + to the motor is supposed to flow through the sensor which again is only 3.3v. That is not enough juice to make the motor go. The motor will run when I connect the battery directly. If I remove the motor and attach an LED as a tester the light does come on. So I know the problem is simply not getting enough volts to the motor. I bought a relay but I cannot figure out how to connect it properly.

Any help would be greatly appreciated. Please keep in mind I am a novice. I am not an idiot:) but this is my first project building a circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
20,000
Seems strange for an output of 3.3v what is the PIR unit?
Sounds like you might need a logic level Mosfet, what is the current requirements for the motor?
A little more detail on the various components helps.
Max.
 

Thread Starter

marshallh

Joined Mar 7, 2018
4
Seems strange for an output of 3.3v what is the PIR unit?
Sounds like you might need a logic level Mosfet, what is the current requirements for the motor?
A little more detail on the various components helps.
Max.
The PIR is a OSEPP PIR-01. I could not find anywhere the requirements for the motor but like I said, when I connect the battery directly to the motor it runs fine. It is a Latrax 370. I don't know what a Mosfet is but I will research that now.
 

MaxHeadRoom

Joined Jul 18, 2013
20,000
That unit is intended for Arduino μ processor, a logic level Mosfet may do it, what is the current requirement of the motor.?
Max.
 

ericgibbs

Joined Jan 29, 2010
9,538
hi m,
The type of PIR modules I use are powered from 5V thru 20V and give only a 3V output signal when activated.
The 3Vout is connected to the onboard IC via a 1K resistor, so max current out is only 2-3mA.
E
 

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Thread Starter

marshallh

Joined Mar 7, 2018
4
Thank you all for your input. I have added a relay but it hasn't helped. I can light an LED in place of the motor but still won't run the motor. The output from the relay is 3.89v. I can connect the motor directly to a AA battery that is only 1.5v and it will run. This is making no sense to me why it's not working. Any more ideas would be awesome.
 

be80be

Joined Jul 5, 2008
2,004
That will not work as The TS has it drawn out there is not enough output to drive a relay.

You need to add a transistor switch to the mix
 

ericgibbs

Joined Jan 29, 2010
9,538
hi burt,
Watched your video, he must be using an intermediate solid state switch transistor/MOSFET between the PIR output and the motor.?
Agreed the TS does not need to use a relay.
Eric
 
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