I intend on using the 2 PWM outputs on my K8055 to drive two model DC Motor speed controllers (3pin the type you would connect to an Model FM reciever).
I have trawled through many of these posts, there are many schematics and CD’s for the actual speed controller. however not much information (that I can find) in regard to hooking up commercial products.
I may just be in a magical, fantasy land in which I can easily plug anything into anything and somehow it all just knows what to do!! . . . . I tried that, it does not work.
No idea but the PWM output of the k8055 isn’t documented very well. The pdf mentions that they exist but only mentions how to use the analog outputs - 0-255.
I never managed to find anything about using the PWM output or how to set them.
Incidentally, most servos require a signal 1.5ms in length every 20ms for the centre position. Windows (apparently) minimum sleep time is apparently 55ms. No idea if thats true but thats what I read somewhere. That being the case, you couldn’t drive a servo from this board. If you can drive a servo, be warned that all of your other features (inputs and outputs) will be blocked by the thread you’re PC is running continually supplying the signal.
Is the input signal of those controllers PWM or is it Futaba’s S-Bus? I think the 1.5 kHz PWM frequency, mentioned in the MC230CR instructions, refers to its output to the motor and has nothing to do with the input signal.
About the K8055 analog outputs: There is no separation between PWM and DAC outputs. PWM1 is physically linked to DAC1. Same for PWM2 and DAC2.
The K8055 operates the “analog” output ports as PWM outputs on a fixed 23.43 kHz PWM frequency. The user cannot control that frequency. The signal is then fed parallel into a BC337 transistor and a TLV274 op-amp. The transistor simply provides the open collector for the PWM output.
The TLV274 amplifier is configured as a voltage follower (full feedback of the amp’s output into its own neg input). Its positive input is in between a 100K charging resistor and a 100nF capacitor. Combined with the op-amp’s slew, this generates the +0…5V DAC output.
I think that would be a use case for J_Holland’s comparator function, that I left out of the initial version of the K8055 Open Source project firmware.
That mode of driving the PWM output allows to generate exactly this type of signal. But instead of trying to hammer the board fast enough with USB messages, you would use one command to set the on/off cycle lengths whenever you need to change them. The microcontroller then does the on/off switching all by itself.
[quote=“MostlyHarmless”]
The K8055 operates the “analog” output ports as PWM outputs on a fixed 23.43 kHz PWM frequency. The user cannot control that frequency. The signal is then fed parallel into a BC337 transistor and a TLV274 op-amp. The transistor simply provides the open collector for the PWM output.
The TLV274 amplifier is configured as a voltage follower (full feedback of the amp’s output into its own neg input). Its positive input is in between a 100K charging resistor and a 100nF capacitor. Combined with the op-amp’s slew, this generates the +0…5V DAC output.[/quote]
So what exactly do these PWM outputs do then? - What can they be used for?
[quote=“tangoforce”][quote=“MostlyHarmless”]
The K8055 operates the “analog” output ports as PWM outputs on a fixed 23.43 kHz PWM frequency. The user cannot control that frequency. The signal is then fed parallel into a BC337 transistor and a TLV274 op-amp. The transistor simply provides the open collector for the PWM output.
The TLV274 amplifier is configured as a voltage follower (full feedback of the amp’s output into its own neg input). Its positive input is in between a 100K charging resistor and a 100nF capacitor. Combined with the op-amp’s slew, this generates the +0…5V DAC output.[/quote]
So what exactly do these PWM outputs do then? - What can they be used for?[/quote]
Anything that can be controlled with a duty cycle on that frequency and within the current constraints. A small light bulb, a tiny electric motor or something like that.
The K8055 is an “experiment” board. It isn’t supposed to directly control your garage door or your drive way snow melt heating elements. It is supposed to turn on an LED, letting you know “I would have turned on X now”. It is “your” problem to convert that “would have” into an actual real world “done”. In the case of the PWMs, this means that it is your job to convert that 0…100% duty cycle into whatever you want it to be.
Here are some K8055 related example projects: roevalley.com/newsbrowser/v- … -index.htm
As a PWM example please see:
“Motor control using pulse width modulation
with one motor and a video
with two motors and a video”
[quote=“MostlyHarmless”][quote=“tangoforce”][quote=“MostlyHarmless”]
The K8055 operates the “analog” output ports as PWM outputs on a fixed 23.43 kHz PWM frequency. The user cannot control that frequency. The signal is then fed parallel into a BC337 transistor and a TLV274 op-amp. The transistor simply provides the open collector for the PWM output.
The TLV274 amplifier is configured as a voltage follower (full feedback of the amp’s output into its own neg input). Its positive input is in between a 100K charging resistor and a 100nF capacitor. Combined with the op-amp’s slew, this generates the +0…5V DAC output.[/quote]
So what exactly do these PWM outputs do then? - What can they be used for?[/quote]
Anything that can be controlled with a duty cycle on that frequency and within the current constraints. A small light bulb, a tiny electric motor or something like that.
The K8055 is an “experiment” board. It isn’t supposed to directly control your garage door or your drive way snow melt heating elements. It is supposed to turn on an LED, letting you know “I would have turned on X now”. It is “your” problem to convert that “would have” into an actual real world “done”. In the case of the PWMs, this means that it is your job to convert that 0…100% duty cycle into whatever you want it to be.[/quote]
Yes I understand that its a “Proof of concept” board but I think thats a bit OTT to then say its supposed to turn on a LED to show that it “would have done this” when there are OUTPUTS that you can wire things up to. While I agree its a proof of concept / experimental board, it clearly provides outputs for you to use and THAT is why I was asking about the PWM on it - because there is nothing really mentioned in the manual.
The manual shows how to hookup a relay, or LED to the digital outputs, shows wires for the analog outputs but shows NOTHING for the PWM outputs. That is why I was asking what they can be used for because there is nothing mentioned about them other than they exist!
You say they can be used for small motors, LEDs etc… but isn’t that the same as the analog output? - I thought the purpose of PWM was that you could pulse the output at chosen intervals?
The way the PWM’s on the original K8055 are programmed in the firmware, one can use some transistor, eventually a MOSFET, to control the speed of even a larger motor. There are example schematics for that here on the forum.
I still have something on my TODO list for the K8055 open source firmware for PIC18F modified boards. That is implementing JHolland’s comparator functionality. On a PIC18F2455/2550 the PWM ports can be used in several different ways. If I understood the code correctly, what JHolland was doing with the comparator functionality was driving them in a way that could be used to control standard hobby servos. They are controlled by a different style of PWM. It is a 1ms to 2ms pulse at a rate of about 25 pulses per second. At 1ms, the servo is full counter clock wise, at 1.5ms it is centered, at 2ms full clock wise. That is a signal the PIC can easily generate interrupt driven using the comparator module.
The most expensive part of converting your K8055 to this new PIC would be the programmer that is needed to get the bootloader into the chip. If you know somebody who has a PIC programmer, the conversion of the board can be done for less than $10. The hardware modification itself is really simple.
