Monostable 555 Trigger release issues

ericgibbs

Joined Jan 29, 2010
21,442
hi d4,
This is what I see with C2 ,1u and R3, 30R, looks OK.
Do you know roughly the frequency the vibrations of the motor affecting the switch.?


E
EG57_ 1195.png
 
Last edited:

eetech00

Joined Jun 8, 2013
4,705
Done. C1 as a timer cap is supposed to be polarized, isn't it?
C3 on your diagram (post #19) is referred as being the Timing cap, and R4 the timing resistor, because they set the duration of the timer.
It can be polar or non-polar, because the signal on its terminals never reverse polarity.
But if polar, honor the polarity markings on the capacitor.
Other than that, use a low leakage cap for the timing capacitor to get reasonable accuracy.
 

crutschow

Joined Mar 14, 2008
38,513
Should C1 capacitor be polarized? Can I use a 30Ohm resistor instead of 10 (thats all I have home)?
C1 as a timer cap is supposed to be polarized, isn't it?
Yes. a 30 ohm resistor should be fine.

Where did you get the curious idea that certain caps should be polarized?
As I previously stated, circuits never require polarized caps.
We only use polarized caps when a large capacitance is needed and polarized caps (typically electrolytic) are physically much smaller for a given capacitance than non-polarized.
A non-polarized cap of the same capacitance and voltage rating can always be substituted for a polarized one.
 

Thread Starter

d4d0m3n

Joined Sep 24, 2023
30
hi d4,
This is what I see with C2 ,1u and R3, 30R, looks OK.
Do you know roughly the frequency the vibrations of the motor affecting the switch.?
Today I took some time, trying to find the best debouncing cap for the switch. 1uF just wasn't enough, 10uF better but not solid, 47uF tantal did the job done 100%, until I mounted the motor straight to the PCB. After that it just didn't stop pulsing.

This is the motor: Mini 610 Coreless Vibration Vibrating Motor DC 3.7V 4.2V 8500RPM Eccentric
Posnetek zaslona 2023-09-26 195829.png

And this is the switch:
SW520D SW-520D Tilt Sensor

Posnetek zaslona 2023-09-26 200222.png
 

Thread Starter

d4d0m3n

Joined Sep 24, 2023
30
Where did you get the curious idea that certain caps should be polarized?
As I previously stated, circuits never require polarized caps.
We only use polarized caps when a large capacitance is needed and polarized caps (typically electrolytic) are physically much smaller for a given capacitance than non-polarized.
A non-polarized cap of the same capacitance and voltage rating can always be substituted for a polarized one.
Thank you, I didn't know that. Long time since I complete electro high school.

As you can see, I'm still struggling to debounce that tilt switch. Should I try putting more capacitors in parallel?
 

eetech00

Joined Jun 8, 2013
4,705
Today I took some time, trying to find the best debouncing cap for the switch. 1uF just wasn't enough, 10uF better but not solid, 47uF tantal did the job done 100%, until I mounted the motor straight to the PCB. After that it just didn't stop pulsing.

This is the motor: Mini 610 Coreless Vibration Vibrating Motor DC 3.7V 4.2V 8500RPM Eccentric
View attachment 303537

And this is the switch:
SW520D SW-520D Tilt Sensor

View attachment 303538
Try connecting a 100nf capacitor across the motor pins to suppress the noise..
CMOS 555 is sensitive to power supply noise, so be sure to connect a 100nf cap across the 555 supply pins.

What is the part number of the mosfet you are using?
Are you driving the motor via a relay? if so relay part number?
I'm also curious as to why you are driving the motor with a 555?
 

Thread Starter

d4d0m3n

Joined Sep 24, 2023
30
6k8 Ohm did the trick! Unbelievable, you guys made my week. Now I will try to lower the cap size, as I still have 47uF tantal through switch.

Thank you so much. You helped me out, like you are from some other planet. I already forgot how good people can be.
 

Thread Starter

d4d0m3n

Joined Sep 24, 2023
30
There's obviously a trade-off between delay and contact bounce rejection.
So you are saying both, R1 and debouncing cap are increasing the delay? Which do you think is affecting it more? Is there some optimal ratio between the two, that I could figure out? Or you think it wont change a lot anyway?
 

crutschow

Joined Mar 14, 2008
38,513
So you are saying both, R1 and debouncing cap are increasing the delay?
Yes, it's determined by the R x C time-constant.
Which do you think is affecting it more?
They affect it equally.
Is there some optimal ratio between the two, that I could figure out?
There is no necessarily "optimum".
The main limit is not going too low with the capacitance, that stray capacitance comes into play, or two large a resistance, that leakage currents affect the operation.
 
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