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Topic: 555 IC as servo driver (Read 2066 times) previous topic - next topic

ReverseEMF

"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

wvmarle

That's pretty much what I had in mind.

Saves a whole lot of balancing frequency/pulse length (those are linked if using a single 555).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

surepic

#17
Oct 09, 2018, 07:01 am Last Edit: Oct 09, 2018, 07:03 am by surepic
Thanks for the link. As was mentioned in one of my posts 556 was in my mind if this option will fail I wasnt thinking of monovibrator mode as wvmarle suggested I was thinkinf of adjusting one 555 for 1ms pulse and second 555 for 2ms pulse with fixed resistors. though monovibrator approach is interesting too one for frequency second one for duty cycle. Purpose is to make 1 device which can turn motor arm to +90 and -90 depending what circuit will be triggered. Price,size and power consumption of circuit matters in my case.

wvmarle

So there's no Arduino or other MCU in the mix? Because that'd be the cheapest option.

Otherwise as you want two 555s anyway, go for that circuit in #15. A transistor allows you to switch on/off a resistor based on an external signal, changing the pulse time (so two resistors in parallel - one with the transistor in series - so if the transistor is off you have high resistance, if on you have the resistors effectively in parallel and a low resistance).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Grumpy_Mike

But dont this servos have pretty wide permissible range ? Over 2ms is they count same as 2ms and below 1ms is same as 1ms.
No that is not how servos work, not the ones I have seen anyway.

I used a 555 as a pen lift servo control in a drawing machine. However the noise made it too jittery to use in the finished project.

surepic

#20
Oct 09, 2018, 12:45 pm Last Edit: Oct 09, 2018, 12:49 pm by surepic
Mike i noticed that noise too while experimenting, via arduino its kinda smoother.

Wvmarle how via mcu is cheaper?
555 timer is 5cents.

wvmarle

#21
Oct 09, 2018, 12:58 pm Last Edit: Oct 09, 2018, 12:59 pm by wvmarle
If there's an MCU in the mix already, using it doesn't cost anything extra, making it cheaper than adding the 555. That's why. It's an Arduino forum after all here!
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Paul__B

forgot to mention I have only 1n4007 diodes but I know they are slower than 1n4148 can this make any issues?
Insignificant at 50 Hz.

ReverseEMF

#23
Oct 09, 2018, 06:25 pm Last Edit: Oct 09, 2018, 06:27 pm by ReverseEMF
Mike i noticed that noise too while experimenting, via arduino its kinda smoother.

Wvmarle how via mcu is cheaper?
555 timer is 5cents.
Yeah, I puzzled over that, too, but then realized two things:
  • It's more than just the cost of the 555.  There's also the support components and the cost of designing, producing, and stuffing the PCB.
  • He was speaking in terms of an Arduino already present -- which means, the expenditure, already happened.

:smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol: :smiley-lol:
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

Grumpy_Mike

Mike i noticed that noise too while experimenting, via arduino its kinda smoother.
Well the noise I am talking about is electrical noise which manifests its self as jitter. This is due to noise on the supply line to the 555 timer. And as I had other servos in the circuit it would have taken a lot of filtering out. This was because I was working on a Raspberry Pi and it only has sufficient hardware to drive two servos. I wanted a third for a pen lift.

Grumpy_Mike

#25
Oct 09, 2018, 07:00 pm Last Edit: Oct 09, 2018, 07:01 pm by Grumpy_Mike
This is the NE555 circuit I used:-

surepic

#26
Oct 09, 2018, 07:20 pm Last Edit: Oct 09, 2018, 07:23 pm by surepic
Well, if this idea wont work then i will put arduino nano or micro and will forget about 555 forever :-))

Mike why you were driving servo via fet instead of mosfet? Isnt it more efficient in this shcematic to use mosfet? Something like 2n7000?

Grumpy_Mike

Quote
Mike why you were driving servo via fet instead of mosfet?
I wasn't, i was using a transistor. I use an NPN transistor to invert the signal and a PNP to switch between the two pulse widths.

Quote
Isnt it more efficient in this shcematic to use mosfet?
No.
You are not providing the the servo with any power, you are just creating a control signal. No need at all for a FET of any description.

BabyGeezer

This is the NE555 circuit I used:-

i'm assuming the whole bottom line connects to GND ?
Attach your images to be viewed directly - THIS WAY;
https://forum.arduino.cc/index.php?topic=519037.0

surepic

yes
i'm assuming the whole bottom line connects to GND ?
yes

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