Hello all! Been reading for years only recently joined. I have a chip problem that is driving me nuts and I have searched as best I can and maybe I am just not asking google the right questions. I have gotten one of these pca9685pw boards cuz I need a ton of servos on a project. That chip totally meets my needs except for the completely unserviceable size of the thing. All the rest of the chips I am using are though hole and down the road when I produce a board I have no problem with working with smaller chips. However, I want to be able to etch a board and move things around refine it. My sausage fingers just don't work well with small parts, and I need things to be solid and attached. Too many times with these small boards they break loose when testing and spoil everything.
So my question is this. Is there a chip that is though hole that has at least 8 channels for servos. More would be better but I can make due with 8. I see a lot of pwm servo chips but none with that many that are though hole.
With a properly-made PCB, I find it easier to do SMD than through-hole. With SMD you only need to place the chip so it somewhat overlaps its pads. The soldering process magically draws it onto the pads.
Often, for prototyping, it is a good idea to make a little breakout that puts the pins into a breadboard-friendly layout. Then you can work with your chip at any size you like. The boards are so cheap these days and delivery really doesn't take a long time.
spycatcher2k:
You could mount one of these to a breakout (or get someone to do it for you) for prototyping, Could have the SMD & through hole footprint on your PCB.
MorganS:
With a properly-made PCB, I find it easier to do SMD than through-hole. With SMD you only need to place the chip so it somewhat overlaps its pads. The soldering process magically draws it onto the pads.
Often, for prototyping, it is a good idea to make a little breakout that puts the pins into a breadboard-friendly layout. Then you can work with your chip at any size you like. The boards are so cheap these days and delivery really doesn't take a long time.
I wish I could just buy the chip on a dip size board package that just went into a breadboard. No extra bits, just the pins to the chip on a board. I think that would be a profitable business if anyone ever did it. I do have some chips coming in the mail and if I have to board them I may just do. I was just hoping there was another one out there that was though hole. I guess it makes sense it wouldn't be if this chip is intended for compact LED system use.
With an uno board? Can all the pins be made into PWM? If so that is really tempting. I wanted to keep the final project flexible so it could be controlled by anything like a PIC or Pi, though it will probably be just an Arduino thing, but I thought it would be cool to keep it hackable. =D
pikadroo:
With an uno board? Can all the pins be made into PWM?
You don't need the Uno board if you don't need it. Just the Atmega 328 chip. You were asking for a DIP format chip that can control servos. The Atmega 328 is a cheap option.
You don't use the Arduino PWM pins for servos - any pins will do. The PWM that analogWrite() produces is not intended for servos. Just use the standard Servo library.
Robin2:
You don't need the Uno board if you don't need it. Just the Atmega 328 chip. You were asking for a DIP format chip that can control servos. The Atmega 328 is a cheap option.
You don't use the Arduino PWM pins for servos - any pins will do. The PWM that analogWrite() produces is not intended for servos. Just use the standard Servo library.
...R
I was under the impression PWM was needed to control a servo?
I was under the impression PWM was needed to control a servo?
Servos are driven by a PWM signal. HOWEVER:
It need not be a hardware PWM output. In fact, the 8bit PWM signals available via analogWrite() are not good for driving servos.
Servo signals have relatively short pulses (1-2ms) at a relatively large interval (20ms), so you can drive a bunch of servos with a single timer by providing them pulses sequentially.
You can probably drive a servo from every pin available on a Arduino, but that wouldn't leave pins for anything else, and could make other programming "tricky." Better to use a separate chip (like another ATmega328, or a second Arduino) dedicated to just the servos (which is probably what most of those fancy "servo controller" boards do.)
Adafruit, Sparkfun, and Pololu all sell servo controller boards, and have excellent reputations when it comes to support...
pikadroo:
I was under the impression PWM was needed to control a servo?
This is due to the use of the same acronym for two very different things.
When you use analogWrite() it produces a signal whose duty cycle can vary between 0 and 100% and the duty cycle represents the proportion of power that the motor driver should apply to a motor, for example. The standard Arduino PWM signal frequency if 490Hz or one pulse approx every 2000 microsecs
The Servo library produces a short pulse 50 times per second (i.e. once every 20,000 microsecs) and ranging in width from about 1000 to 2000 microsecs. The servo interprets the width of the pulse as the angle that the servo arm should move to.
Because there is a large gap between servo pulse it is possible for an RC transmitter to send pulses for several servos in the way illustrated in Reply #14. The RC receiver can then separate them and always send (say) the first pulse to the aileron servo and the second pulse to the elevator servo etc.
Well, then that opens up the possibility of i2c between two Atmega 328... Interesting... Didn't consider this at all, mainly do to misunderstand. I think that fits the bill cuz I would still be able to change control systems that way, I get to use pretty basic libraries and no need for boards or chips can't immediately work with. I LOVE IT!
Re: an earlier comment, the folks at www.proto-advantage.com offer SMT to DIP boards for a large range of parts, and will order parts from Digikey and mount them to boards for you for a couple bucks.
pikadroo:
I wish I could just buy the chip on a dip size board package that just went into a breadboard. No extra bits, just the pins to the chip on a board. I think that would be a profitable business if anyone ever did it. I do have some chips coming in the mail and if I have to board them I may just do. I was just hoping there was another one out there that was though hole. I guess it makes sense it wouldn't be if this chip is intended for compact LED system use.
