Pulse Width Modulation
Joseph Lopez
I'd just post this as a discussion for now.
From all the different sites I've been reading, there's really no
magic number as far as what frequency we should use to control the
motors. The robot designs I've seen don't comment on their numbers as
far as PWM is concerned, and the general consensus in the different
forums I looked at is to experiment with the motor to see what
frequency works best for the given application. I found some places
that said 1KHz - 200KHz were common modulation frequencies, and others
that said 10KHz - 15KHz were good for most applications.
Things that we'll have to consider though: 1. The human auditory range
is around 20Hz - 20KHz. This means that depending on our frequency,
there is a possibility of generating annoying noise whenever we're
generating the pulses. Again, we'll only find out how bad a problem
this is by actually testing it. Given how loud the bot is when the
motors are running, this probably won't be a problem. 2. RF
interference gets worse as the frequency gets higher, so we might
eventually run into problems transmitting to and from the robot when
we eventually get to this stage. No numbers were given on this, so I
don't know.
In any event, the Robot Room website had an article showing how to
implement a PWM circuit without a microcontroller. I haven't tried
testing it yet in multisim, but I'll try to do it tomorrow. I've put
the site below for anyone that's interested.
http://www.robotroom.com/PWM.html
zonemikel.com
| If you're using a micro controller the frequency does not really matter, its the "duty cycle" that matters. For instance if we are transmitting a array of 10 bits over and over and we transmit 1111100000 that is 50% duty cycle. If we were going to do it with a mcu that is what we would do ... just transmit a small (binary) array of numbers to the base of the transistor controlling the motor. I ordered some stuff from mouser i now have five of these pwm things if you want to see how they work https://www.mouser.com/Search/ProductDetail.aspx?R=UC3842BNGvirtualkey58410000virtualkey863-UC3842BNG Do good, Be Well, Michael --- On Sun, 3/7/10, Joseph Lopez <jolo...@gmail.com> wrote: |
Joseph Lopez
want to apply to the motor to run it at the desired speed. Source
voltage X Duty Cycle = Voltage to motor. We need to figure out what
speeds we need the motor to run at, and what voltages are necessary to
get those speeds. This will probably be dependent on the control
circuitry coming from the sensors.
On Mar 7, 9:39 am, "zonemikel.com" <zonetejasmi...@yahoo.com> wrote:
> If you're using a micro controller the frequency does not really matter, its the "duty cycle" that matters. For instance if we are transmitting a array of 10 bits over and over and we transmit 1111100000 that is 50% duty cycle. If we were going to do it with a mcu that is what we would do ... just transmit a small (binary) array of numbers to the base of the transistor controlling the motor.
>
> I ordered some stuff from mouser i now have five of these pwm things if you want to see how they workhttps://www.mouser.com/Search/ProductDetail.aspx?R=UC3842BNGvirtualke...
>
> Do good, Be Well,
>
> Michael
>
> --- On Sun, 3/7/10, Joseph Lopez <jolope...@gmail.com> wrote: