Hi! Look at the led paralleled with motor. According to diagram, it is directly connected to battery. Try invert the connection.

 

Yes thanks, I noticed. I tried without the LED even.

Take some good pictures of what you have most pir's have two settings sounds more like you have it set wrong one setting it comes on and stays a bit one it's more like pwm it just triggers fast..

yes, I thought of that one too, I'm aware of the two settings. Did some test with the PIR alone and worked fine. Thank you.

You could also use a meter to measure current draw coming off the battery. Then look at the current draw of the motor. I suspect you have more current going somewhere than you think you do.

It's definitely current related.
Measured the draw:
- 4 AAA (6v) : motor draws 50mA. Doesn't run.
- 1 6F22 (9v) : motor draws 50mA. Doesn't run.
- 1 23A (12v) : motor draws 20mA. Doesn't run at all.
- 2 AA (3v) : motor draws 90mA. Runs fine.
- 2 D (3v) : motor draws up to 130mA. Runs like crazy.

I feel so dumb.

 

That is not a simple DC motor in its common form, there is some other kind of controller, are you sure it is a simple DC brushed and not a BLDC with internal control?
Max.

 

It's not unreasonable to expect someone to learn to use a tool properly before they attempt to use it. Suppose you just bought a table saw (like I recently did). Would you rush to cut some wood with it without first reading about safe operation? I hope you answered "of course not". I'm scared to death of my table saw and take every precaution I can think of, which was expanded by extensive online research.

I know that using a transistor is not nearly so scary, but it's good form to understand a component you intend to use in a design.

Petkan:
The fact that the battery sags from 6V to less than 3V points that the load (the motor) is too heavy i.e. meant for lower voltage.
Instead of using a mosfet, you can use a Buck (in on off style) making say 3V out of 6V. This will halve the consumption seen by the battery.
You can manipulate the Buck enable the way you controlled your MOSFET.

 

Yes thanks, I noticed. I tried without the LED even.


yes, I thought of that one too, I'm aware of the two settings. Did some test with the PIR alone and worked fine. Thank you.


It's definitely current related.
Measured the draw:
- 4 AAA (6v) : motor draws 50mA. Doesn't run.
- 1 6F22 (9v) : motor draws 50mA. Doesn't run.
- 1 23A (12v) : motor draws 20mA. Doesn't run at all.
- 2 AA (3v) : motor draws 90mA. Runs fine.
- 2 D (3v) : motor draws up to 130mA. Runs like crazy.

I feel so dumb.

Petkan:
The morale is that your motor is meant for lower voltage (i.e. higher current).
If you want to stick to 6V on other than the motor grounds, insteaf of a MOSFET you could use a Buck regulator (in on off style) making say 3V out of 6V . This will halve the current seen by the battery.
Size and cost is comparable and you manipulate the Buck enable like you controlled your FET

 

Just wondering what the pulse width is you are working with out of the PIR? On a single pulse, how long is the motor to run? Maybe the reduction in voltage is really being done via the switch (MOSFET or Transistor) being modulated by the output of the PIR?

 

This post is becoming a little bit strange with all those saw stories and missing fingers...(the video with the sausage is impressive)
I sympathize with you all though, good thing that I'm battling against a little transistor myself.
(even if I burnt me a finger with the soldering iron yesterday )

Anyway, I know what you're saying, I've been throwing every solution that I can think of, but nothing is sticking. And I have to present this finished project on Tuesday.
I thought that I could get away by just adding more voltage. The 9v battery seemed to work too well. But the motor gets 3v at the beginning and then slowly and steadily starts loosing voltage and in about 10 minutes it doesn't move any more 'cos is getting barely 1v.
Then I turn it off, wait 10 minutes and turn it on it starts at 3v again.

Nothing seems to be overheating, I can touch the transistor, not hot at all. And I have put a base resistor already.
The fact that when I use a 12v A23 battery doesn't work at all, and with the 9v it works for 10 min. makes me believe that the problem is something related to the amperage (Even if my little motor draws barely 50mA when loaded).
For the moment I'm going to try again with a MOSFET instead the BJT and the 9v see if its better...(too bad I soldered everything already!!)
Thanks for your help again, keep on trying...!

 

Sounds like you are pulling the battery down, leaving it a while and it recovers a bit. All cells and batteries have internal resistance to overcome
As said by others, you need to find what the motor is pulling with a meter in series with the motor supply. You could do this with the PIR out of circuit.
Alarm type PIRs work on 12-volts and give a clean output, usually through a relay. Your PIR might not be giving a clean output. I'm not sure or haven't read if you want the motor to just stop and start or respond to the distance of the target from the PIR. Either way, you need to know what it is doing.
All cells and batteries have internal resistance that must be less than what you are trying to pull. A 6-volt lead acid would have a low internal resistance. Don't know if you have tried a power supply instead of a battery?

 

Do you have any kind of scope so you can see if it's not in a single state. I.E. the module is pulsing, not giving you a consistent output. I've never used one of these, but the document you specified states:

• Output: Digital pulse high (3V) when triggered (motion detected) digital low when idle (no motion detected). Pulse lengths are determined by resistors and capacitors on the PCB and differ from sensor to sensor.

Sounds related to what's going on with the voltage. If you can check the output of the PIR (gate) you'll know, if you have a scope. When the mosfet is turned on, there's like ~5 mil-ohms of resistance, so that shouldn't matter.

It's always suspicious when someone is building something that runs on three volts, yet powers it with twice that???

If you can find a scope you can probable figure out what's going on. I suspect that it's that pulse width you are not taking care of.

 

I made a big mistake believing that I could replace the original AA batteries by the smaller AAA and obtain the same results.
Once I went back for the AAs everything worked perfectly.
I even reduce the volts from 6 to 4.5. Good enough to power the PIR and the motor.

Thanks to you all, you really helped me finding the problem.
(I will soon show you the finished project).

 

Great, I'm glad it all worked out. Just out of curiosity have you tried it with a 3v supply? I think it could work depending on the PIR (some are 3.5v min.) Good luck thanks for letting us know...

P.S. did you get to scope it. I'm curious about the 'pulse width' angle.

 

No I haven't tried. The PIR documentation says "3V-9V input voltage, but 5V is ideal". I trusted it.
But I'm going give it a try why not.

And no. I don't have the tool to test the pulse sorry!

 

I even reduce the volts from 6 to 4.5. Good enough to power the PIR and the motor.

Remember that 3 AA cells in series is only 4.5 volts when the batteries are new and fresh. The voltage will drop to as little as 0.9 volts per cell (2.7 volts for 3 cells) at end of life. Even 4 cells in series will not maintain 5 volts for the specified capacity of the battery.

 

Remember that 3 AA cells in series is only 4.5 volts when the batteries are new and fresh. The voltage will drop to as little as 0.9 volts per cell (2.7 volts for 3 cells) at end of life. Even 4 cells in series will not maintain 5 volts for the specified capacity of the battery.

Heisenberg uncertainty principle

 

Tried with 3 volts, it works but not enough power when loaded.
I'm sticking with 4.5v, hopefully (and uncertainly) the batteries will last a couple of months...

 

Does the battery voltage (at the batteries) drop when you load it with a 3v supply? If you follow the power line to the motor you should see a drop in voltage, if the supply isn't supplying enough voltage. Might want to do that anyway just to know what's going on. Have you measured the current draw on the batteries, with and without the PIR module working? This will give you some idea, but batteries are not really dependable and it's worse when you series them, as you will find the worst battery, is the best you get.

What is the final schematic of this beast? Do you still have the resistors and leds on the board? Of course these draw current....

 

Little drop in voltage with 3v, I was getting 1.50v at the end (and 2.70v with 4.5v).
Here's the final working schema:

I'll post a video of the thing soon.

 

Have you achieved what you set out to do?
PIR goes high/low, turns transistor on, switches motor on.
Been hard work. And if you use a single pole, double throw switch the way you have drawn it, you aren't out of the woods yet - it's just switching thin air. But that's nit-picking.

 

"I was getting 1.50v at the end", which end? When it ran out of power or when you followed it via your meter, motor voltage? There will be a junction drop across the transistor of about .6 volts, but I can't see why you are losing 1/2 of your voltage. It still keeps me wondering if you are getting 'pulses' out of the PIR (as the ad shows) and it's not really switching on for duration, but only for the pulse width. That would give very similar results on a multimeter. If I had the parts I'd build one, just to see myself.

Maybe someone else has that PIR module and can update us (at least me) on how the pulse width works. I know it varies by manufacturer of the total board and some appear to have jumpers on ways to configure the output.

I keep trying to think of a way for you to measure or check the pulse width. Even though I'm now just a hobbyist, I know the value of the proper tools and know they cost money. Too bad you don't have access to a scope, we'd know quickly where the problem lies. I purchased a low cost one ($400 US) that is super (Rigol), but it's costly. I know it's like having a 50 cent circuit that doesn't work and somebody tells you to hook up a million dollar box to it to diagnose its problem... Do you have an Arduino board? That would be quick enough...

Somethings fishy about how that's working... Maybe someone with that module will speak up. I know I seem fixated on the 'pulse' thing, but it does fit the data and nobody that I know (in this thread) has ruled it out.... That makes it an unknown and questionable.

I hope you have fixed the hardware so that the switch is correct, I'm ASSUMING??? Or you would not have voltage anywhere...

BTW what does the motor drive and why does it need to be battery operated? Just curious...

Thanks for keeping this an open thread. It's always nice to see something to completion.

 

1.5v when I followed with my meter motor voltage. I assumed that it is the PIR that is using the other 1.5 volts (?)
You're right, I'm not ready to invest $400 in a scope yet. But I'm definitely going to continue making electronic things so one of this days maybe...?
I do have an Arduino, but the machine is going to be shown tonight and I won't be able to get it back any time soon...

And yes the switch is working! I didn't notice that big red line on the diagram .

I'm kind of in a rush today but I'll post a video of the finished project soon, promise.