hello, i'm trying to use a servo with my picaxe. I tried it on Arduino before, and it worked just connecting the pins at the right position, without resistors.
now i just connected the same way on the picaxe, and it doesn't move.. I then remembered that in the "start here" project, a resistor was used.. So the question is: is it necessary? why do i need a resistor? and how do i wire it ?
Another thing that is probably messing up.. i have the darlington chip there.. shoud i remove it?
thanks :)
A guess
No-one’s replied to this, so I’ll stab a guess. A complete guess, bearing in ming that I’m not familiar with either picaxe or arduino.
Start with a question: Do you know if the transistor collector is the inverse of the base? There are several darlington arrangements and I don’t know which is in use. I.e, are you putting in a “1” and getting out a “0”? That would certainly cause the servo not to work as the variable length 1-2ms pulse MUST be a “high” pulse with the line left low for the remainder of the duty cycle.
I connect my servos to
I connect my servos to the PICAXE outputs with 330 ohm resistors, without a darlington. This seems to work fine.
Duane S
Wilson, North Carolina USA
Sorry for not answering this
Sorry for not answering this before:
A) You should NOT use a darlington before a servo. Just as you should not use a darlington after a serial signal etc. Darlington is only when you want to add a little more power, not when you want to send signals. And the servo just needs signals on the signal-wire! It has 3, the other2 are providing the power.
B) No one knows what the deal is with the resistor. That is the truth, any one saying different is lying. There are lots of theories, noise, redusing signal strength, sinking etc… but the truth is that nobody really knows. You should just always ad a 330 ohm resistor between a TTL chip and a servo, that is how it is! (Do it!)
I’ve run with and without,
I’ve run with and without, for the most part though, I’ve read that it’s good to have at least a 220ohm res for any of the i/o pins on a mcu…just in case.
Well, in general, resistor
Well, in general, resistor would be needed to reduce current through/voltage on the servo. May be servo internal resistance is usually small, which implies a current which might be too stong for either MCU or the servo itself… so it would make a lot of sense to put some resistor there just to reduce the current. TTL high level is 5V, if Rservo is measured in single digit Ohms, current strength would be in Amperes (rather than milliamperes)… can be disastrous for the chip, I guess.
I told you; No one knows
I told you; No one knows why, but just add it ;D
Current
It’s to reduce the current in the servo signal line. Presumably this affords the circuit some protection if some artist acudentally passes the drive voltage in there instead of the TTL signal out from the MCU. Personally, I’ve never bothered.
[edited about 0.78 seconds later] just realised peter_al replied in the next thread rather than replying to this one.
Yawn, another theory. Nobody
Yawn, another theory. Nobody knows why that thing with the 330 in front of the servo. And that is fine, it is like "what is outside the universe"-kind of thing. Theories, theories, just add it.
Nobody knows why, and it is alright. Peace!
I know!
…I’m just not telling you because the last time I told you how something works you called me bad names like “techie” and stuff. Besides I don’t want to spoil the illusion that it all hangs together by magic.
Oh, and another thing: Santa Claus is REAL. Don’t let anyone tell you otherwise.
Sorry if it ever came out
Sorry if it ever came out wrong; "techie" is NOT a bad thing to be! Us artys would be nowhere without you. Absolutely! You are the key!
loool 
PS Thanks
loool
PS Thanks everybody for the responses!
Uh, well, as a certified
Uh, well, as a certified “arty” I can tell you now, that even if “no one knows why”, you can figure it out. 
All you need is knowledge of Ohm’s Law and reading MCU and servo specs. It’s way simpler than “FritsLDR”, seriously… 
C’mon, BOA,Everyone KNOWS
C’mon, BOA,
Everyone KNOWS that Santa Claus is real. As are the Easter Bunny, and the Tooth Fairy.
They have been discussed over and over, everywhere on the internet. It has been firmly established that they are real.
So, please don’t drag Santa into this again. He’s very busy this time of the year.
Everything electronic is based on EMS. To doubt that is to challenge it. Thomas Edison tried to challange it, but gave up.
Like most of us, you apparently do not fully understand EMS. Fortunately, EMS does not need to be fully understood to use it.
We all use it every day, but very few of us fully understand it. Instead, we appreciate it for what it is, and use it as best we
can.
Duane S
Wilson, North Carolina USA
** O.K. Peter,Can we not be**
O.K. Peter,
Can we not be so serious here? I think that what frits was trying to say was “just use a 330 ohm resistor”.
I know Ohm’s law. Very well. And I feel sure that frits does also. But I also know that there is no way that I could ever explain it in other than my native language.
If you want to post a walk-thru of Ohms Law (in English or Danish ) then please feel free to do so. Or if you’d like, an explaination of EMS.
Most of the people here do not have Electrical Engineering degrees, or even any experience in electronics. They are here as hobbyists, and just want to know how to solve a problem.
Best regards,
Duane S
Wilson, North Carolina USA
Real? I always declare him
Real? I always declare him an integer. Way more efficient.
Just for the record; I do
Just for the record; I do not know Ohms law.
I tell you all because if someone out there is like me, I want to send the messege; You do not have to know it t have fun. I know no electronics.
Ha Ha Ha ! Well, you’ve
Ha Ha Ha ! Well, you’ve certainly fooled me.
You do make a very good point. One does not have to be an electronics Guru to have fun with electronics.
Duane S
Wilson, North Carolina USA
