A tablesaw is far more challenging than a transistor.

And I disagree. Depends on your interests and training at a young age.

 

I suppose I should have specified that using one safely and with precision requires more attention. Turning it on and passing wood over the blade isn't tough.

 

One thing that circuits and table saws have in common...the first project you do is only the beginning of a long journey.
I am good with a table saw, I am pretty good within my little area of analog design, but every project requires learning, whether it's your first CD4060 timer chip or making a jig to produce a finger joint (box joint). The more you do, the better you get, but you're always learning.

Learn both and you can have blinking LEDs in your coffee table.

 

I don't have a tablesaw, but I bought a scroll saw last month (all right far less deadly) and I did what I wanted right away, in half an hour maybe. Never touched one before.
It's been close to two months that I'm trying to make this simple circuit work without success.
And I'm sorry, but I believe that there is something more than a simple formula.
Yesterday everything worked great, the motor was getting 1.7v and running perfectly.
This morning (didn't change anything!!!) 0.5v and not moving at all! ?? how come??!!!
and if I let it run for a while, voltage increases little by little 0.6v then 0.8 and finally around 1v but no more.
why??
don't get it.
Tablesaw you do a clean cut, a twisted one, or cut yourself a finger, at least you know well where you're at.

 

This morning (didn't change anything!!!)

Not intentionally. But something obviously changed. A poor breadboard connection perhaps?

 

I'm giving up. Checked everything 10 times, cannot find what's wrong.
I'm going to change the 6v AAAs for a 9v battery.
Not the ideal for the 1.5v little motor, I may have to slow it down now...

 

I'm going to change the 6v AAAs for a 9v battery.

If you are talking about a PP3, "9V transistor radio battery", your making a bad decision. They are not ideal for a motor, they have voltage but not amperage or a long life in motor applications. https://en.wikipedia.org/wiki/Nine-volt_battery

 

Yes a PP3. Just tried and the motor runs like crazy. Too fast.
Tried a 12v A23 too, and strangely I had the same readings than with the 6v AAAs. The motor got just 0.6v at the end.

What do you suggest that I use instead?

 

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.

Dad training. Training from work machinist's. We all eventually said that the table saw was the most dangerous piece of equipment in the machine shop at work, but there are still basic precautions. I was somewhat familiar with the lathe and mill in high school. Anyway, I did end up with 24/7/365 day access to the machine shop unsupervised.

The TIG welder I had in my hand and did very well when set up. The MIG welder, I also had in my hand and also did well, but the department head put it off limits to all but one person. I tried stick when I was about 18 when there wasn't auto-glasses and also did well. Brazing and working with quartz and pyrex was also fine.

For a really cool table saw, see https://en.wikipedia.org/wiki/SawStop. In it's normal mode of operation, it won't cut a hot dog and it will cost you at least $70.00 for each "infraction".

See: https://www.bing.com/videos/search?...3707988E3F499987893E3707988E3F49998&FORM=VIRE

A cool application of electronics. The shaft size is huge. I did see a saw at a local Woodcraft up and personal.

 

We all eventually said that the table saw was the most dangerous piece of equipment...

The table saw is scary powerful. That causes intelligent people to be cautious. The quiet little drill press isn't very frightening, but it can spin a piece of sheet metal right through your hand. My point is that deception is more dangerous than big, scary, growlers. It's the one you don't see coming that gets you.

 

As a general rule, accidents usually happen when familiarity breeds contempt.
Max.

 

As a general rule, accidents usually happen when familiarity breeds contempt.
Max.

There is some value in that statement, but I feel a personal rejection of it because I don't suffer from contempt of tools (or electricity). I've seen beginners upon whom I didn't bet whether they would ever be good (at their job), I bet on whether they would survive the first year. After the beginner stage, fools still get careless, and they have a lot more years to get careless than a beginner does.

I guess your advice is a good thing to tell an average population, but this site does not contain an average population. It contains a lot of people who lived to be rather old in an environment where a single mistake is often fatal.

 

Deception: My bloodiest work mistake (personal business) involved the file. I was making a lathe cutting tool and the file slipped. Finger into cutting tool. Bloodies home mistakes were"chainsaw kickback" and splitting my pinky finger with a pinch from a hammer. Both should have required stitches. I also did the not securing a piece of sheet metal that turned into a rotating sharp cutter.

At work I was sealing with a hydrogen/oxygen torch, red phosphorus and zinc in quartz evacuated tube and it fell. Quick thinking, I smothered it.

I never did get zapped by deadly power supplies that I was fixing. 15 kV @ 3A; 100 kV @ 0.1 A; and 1000 W RF at 13.56 MHz One of those systems was powered by 90 A, 3 phase 208 VAC.

 

Back on track.

The lack of a base resistor and to some extent a a gate resistor and the lack of a proper heatsink will degrade a circuit. Not sure what, if anything, is appropriate here. Can you touch the MOSFET/transistor or is it too hot when running? That's what I see in my crystal ball.

 

The table saw is scary powerful. That causes intelligent people to be cautious. The quiet little drill press isn't very frightening, but it can spin a piece of sheet metal right through your hand. My point is that deception is more dangerous than big, scary, growlers. It's the one you don't see coming that gets you.

 

Dang you got my hand someone on a cellphone caused mine the took the call and dropped the board.

 

I'm giving up. Checked everything 10 times, cannot find what's wrong.
I'm going to change the 6v AAAs for a 9v battery.
Not the ideal for the 1.5v little motor, I may have to slow it down now...

Don't give up on something like this.
I'm no expert at electronics and have very little formal training, but in my past life, I had to find solutions to problems that were time critical.
My solution was to throw solutions at the problem until something stuck. That bought you some breathing space, then you could whittle the problem down.
I would break the project down into two parts - the PIR and the motor. Get a clean output from the PIR. Use a Schmitt or similar to get a clean digital signal, test it with an LED or scope. Then use that output through a simple NPN (with base resistor etc.) to drive the motor. Trying to do everything at once is too tricky. You will feel much better if it works.
I find the same approach works with MCU projects. I'm way past ever wanting to be a code guru, but I like things to work. I will cut and paste from other folk's work until it works for me. I simply do not have the hours in the day to learn all the theory, use it once then forget it 6-months down the line

 

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.

The lack of a base resistor and to some extent a a gate resistor and the lack of a proper heatsink will degrade a circuit. Not sure what, if anything, is appropriate here. Can you touch the MOSFET/transistor or is it too hot when running? That's what I see in my crystal ball.

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...!

 

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..

 

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.