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/diy/ - Do It Yourself

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753557 No.753557 [Reply] [Original]

Something happened that i haven’t been able to explain , I wrote a program to output a PWM signal, this to activate a transistors base using a PWM which I could change the frequency using a potentiometer, the program worked fine, and the circuit too, however something was happening,

1) When I lowered the frequency of my PWM the motor stopped spinning however a “buzz” could be heard from inside the motor

2) When I tried to verify my PWM signal using an oscilloscope, like in the picture, , a spark came out at the tip of the probe and the circuit stopped working, the microcontroller on my board died, (it just gets way to hot in seconds) however I still have no idea why this happened,

Hopefully someone here can explain to me what happened, I did plug my PWM signal directly to the oscilloscope before with no problems however when tried to debug in the working circuit this happened, as i recall the probe was gorunded with the circuit , but you might also want to consider the case of it not being grounded

>> No.753562

ESD perhaps?

>> No.753563

>>753562
i was working on an antistatic mat

>> No.753564

Check the transistor to see if it's still good

>> No.753565

>>753564
mm i dont have it at hand atm

>> No.753566

>>753557
I haven't worked too much with DC motors but wouldn't you change the duty ratio of the PWM instead of the frequency if you want to change the torque?

Also you seem to know what you are doing but just to make sure: You didn't hook up the ground of the probe to some arbitrary point, right? You do know that the ground on the probe is tied to earth ground.

>> No.753567

>>753566
i do know it is mains earth bounded, however all my grounds where at the same node, the problem happened when putting the tip (positive) probe to the PWM

>> No.753576

>>753557
>When I lowered the frequency of my PWM the motor stopped spinning however a “buzz” could be heard from inside the motor
because the frequency was too low.

> When I tried to verify my PWM signal using an oscilloscope, like in the picture, , a spark came out at the tip of the probe and the circuit stopped working, the microcontroller on my board died, (it just gets way to hot in seconds) however I still have no idea why this happened,

dunno how you fucked that up. spark comes from high voltage differential, so if your probe somehow got massive and the PWM was going negative or something.

I dunno but that last bit sounds nuts, if it fried the cpu then i'd be pulling too much current or something.

could it be that attaching the probe pushed two wires together? like how "nice and neat" is it?

>but you might also want to consider the case of it not being grounded
then a variety of things, including it fucking up, could've happened.

>> No.754363

did you use a pc supply

>> No.754394

>>753557
There is this general rule of thumb, when conecting somthing like an electromotor or something that needs high voltage, don't connect it directlly to your micro controller. you should've used something else than a transistor scince it is a dc 'motor'. galvanic seperation ftw. also you should've used a resitor before measuring your PWM. you short circuited it, the spark was probablly the 12 volts to negative 5 volts. if your transistor is toast the last one is true aswell.