Help with simple circuit

Thread Starter

Hopper30

Joined Aug 17, 2022
2
Hello, I am a newbie with limited circuit design knowledge. I am trying to make a small simple circuit that has the following characteristics:

1. As small as possible
2. Battery powered
3. PIR sensor trigger (close range less than 1 foot ideally)
4. When triggered runs tiny electric motor for 2-3 seconds and then shuts down motor.
5. Delay of a few seconds before triggering again.

I will need to purchase the parts from amazon in canada as I am not close to any outlet to buy otherwise.
Any help with this design and specific parts would be helpful. My apologies if this is vague and easy to design but looking for any help I can get.
Cheers
 

WBahn

Joined Mar 31, 2012
26,873
Try to be more specific in your requirements. Remember, the people reading them have no idea what your constraints are.

1. As small as possible
So something like a custom ASIC? Nothing else is likely to be as small as this, and thus not meet your requirement.
Got a couple hundred thousand to cover the design, layout, and fab.

2. Battery powered
So a golf cart battery would acceptable?
It's okay if the battery drains dead in ten minutes?

3. PIR sensor trigger (close range less than 1 foot ideally)
So any beam pattern at all?

4. When triggered runs tiny electric motor for 2-3 seconds and then shuts down motor.
How tiny? A MEMs motor that is much smaller than a human hair? A stepper motor?

5. Delay of a few seconds before triggering again.

Start with your true requirements. What is absolutely essential for what you are trying to achieve. My guess is that it's the motor. So first figure out what kind of motor you can work with and figure out what is required to drive it in terms of voltage, current, and waveforms. Estimate how often it will be triggered and then give yourself some cushion. That will put you in a position to determine the kinds of batteries that are suitable to power the motor for the length of time you need the battery to last. Once you have an idea of the size of motor and battery, you are in a position to put some goals together regarding the size of the circuitry.
 

Thread Starter

Hopper30

Joined Aug 17, 2022
2
Excellent points. Thanks for providing such a detailed response.

The motor would be a small less than 12v DC motor. It doesn't have to be tiny but small enough. I am trying to make the whole package as small as reasonable but something less than 1-2 inches in size would be sufficient.
I would like the battery to last as long as possible. The motor will not be triggered all that often so the majority of the time the system will sit in standby until the PIR sensor is triggered.
I was hoping to use the following components that I have managed to find.
HC-SR501 PIR Infrared Sensor Body
Mini Generator Motors 3V-12V DC Motor Electric Motor
 

WBahn

Joined Mar 31, 2012
26,873
This is movement in the right direction. But you REALLY need to avoid saying things like:

I would like the battery to last as long as possible.
Take a moment to think about it and you'll realize that this statement adds absolutely no value. In all the years that I've been an engineer, I've never heard anyone say that they would like the battery to not last as long as possible.

Again, remember that we have no idea what you are trying to accomplish. I can think of applications where having a battery last for 30 minutes as the price for making the battery small enough would be absolutely fine, while other applications would be a non-starter unless the battery would last at least six months.

So take a moment and ask yourself things like: If the battery lasted a day, would that be good enough? If the answer is yes, ask the question again with half the time. If the answer is no, ask the question again with twice the time. Keep at this until you can make a statement like, "If the battery would be expected to last more than 60 days, I'm willing to consider a smaller battery that won't last as long, but if the battery would only be expected to last 15 days, I'm gonna have to use a bigger battery to increase that.

Note that whatever you come up with is not engraved in stone. As the design and testing progress you can revisit the specs, if needed.
 

BobTPH

Joined Jun 5, 2013
5,467
Since you are seeking help, why are you keeping us in the dark? Why not tell us what you are trying to accomplish instead of what components you think you need?

Say you have picked small motor, and we help you select a battery and the electronics. Then you come back and tell us it doesn’t work because your small motor cannot lift a 10Kg object one meter in 3 seconds. We all do a face slap at that point., and are not happy with the time we wasted.

So tell us what you are trying to do. Something like this:

“I have a model railroad. I want to close a crossing guard when a train is approaching. The crossing guard is 3cm in length and weighs 25 grams.”

This would get you much better answers, including things you never thought of.
 

bidrohini

Joined Jul 29, 2022
66
You can proceed with an Arduino UNO, an L293/L298 DC motor driver, a 6V DC motor, A PIR sensor, a 9V battery and a
9V Battery Connector with Power Jack.
 
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