Preliminary PWM actuators release

Brewer · August 6, 2015, 7:41pm

I couldn’t get the update to work. I tried through the web interface and I get:

Checking hex file size with avr-size…
avr-size error: avr-size: /var/www/uploads/brewpi-0.3.0a-core.bin: File format not recognized

I tried using DFU method and get:

Opening DFU capable USB device… Programming done, now resetting EEPROM to defaults
Opening serial port
Aug 06 2015 20:29:57 Opening serial port
Aug 06 2015 20:30:08 Errors while opening serial port:
Could not find compatible serial devices

Elco · August 6, 2015, 10:57pm

I have removed some posts in this topic to provide a summary here: @Brewer has been a great help finding the flaws in my instructions and apparently my dev system is a bit different.
I have updated the instructions (see release on github) and hopefully the second person to try this will have a smoother ride.

Dan · August 6, 2015, 11:37pm

Hey @Elco just wondering what is the theoretical upper limit for PWM period? Not an issue for this release but in the future we will want to use PWM actuators for controlling fans and pumps etc. This will require a much faster period.

Longer term it could be worthwhile displaying the PWM duty cycle for used actuators on the screen (and maybe have the ability to easily manually adjust it for fine tuning).

Enjoy your break!

Elco · August 6, 2015, 11:49pm

Hi Dan,

PWM could be very fast, if it is offloaded to internal PWM controllers in the processor.
If the main processor is involved, this would require all other code to be non-blocking, or multi-threading.
But I have not looked into hardware PWM capabilities for the Spark/Photon yet, because for AC current, it is not suitable anyway.

What I think would be a better approach would be to release a PWM pump/fan controller board: a simple board with it’s own microcontroller to do PWM, and a few output options: 0-5V, digital PWM and open drain PWM. So a board with transistors and diodes to handle switching large currents. And for example a molex connector for PC fans.

The board can communicate with the BrewPi Spark over RS-485 and even speed control could be offloaded, for fans that support it.

Elco · August 8, 2015, 11:42am

Before I go, some quick tips for tuning the PI controller in advanced settings:

tune in fridge constant mode
you can view the current PWM value in the device list if you check ‘read values’
Start with Ki at zero to tweak Kp, set it so you get minimal overshoot on a temperature step, but still approach it quickly enough. The steady state value will be slightly under setpoint.
increase Ki so after the step it will slowly increase the PWM value to compensate for energy losses and the temperature will slowly reach the setpoint. Don’t make Ki too high: it will go to setpoint quicker, but it could cause it to oscillate.
tune at the setpoint you intend to use later

Borisfa · August 19, 2015, 2:26pm

@Elco, this PWM works only in Brewpi Spark? Or it can be used in Brewpi Arduino+RPi?

Thanks,

Fabiano

SwiftPint · August 27, 2015, 9:39am

Thanks Elco.
I had a bit of a play at the weekend. I managed to get the latest release installed OK, and had a bit of time to play around with the settings. It was working great controlling my BIAB kettle, testing with about 12 litres of water. I had a bit of a tweak with the PID settings and was getting it dialed in quite well. I still need to do a bit more testing, but am impressed with how well it was working.

Hope you’ve had / are having a great (and well deserved) break! Looking forward to more updates.

Elco · August 29, 2015, 8:05am

It is Spark only for now.

@SwiftPint
Thanks for the feedback. Had a great holiday. I tested the PWM release on my fridge, but there is a bug in the cooling PWM generation… stay tuned.

molc · September 30, 2015, 9:05am

Is the bug still present in the PWM release with fridges? I’d like to try this system with my HERMS, but I don’t want the fermentation control to cause an issue and ruin a batch of beer if I apply the update, as I’ll be using the same Spark for fermentation control after mash.

Alternatively, if it was possible to easily switch between modes (old control and new PWM control) that could be quite useful, as we could turn on the experimental pid class for mashing and revert to the reliable fermentation control for fridge control.

Elco · September 30, 2015, 6:16pm

The bug is still present. I am doing the proper refactor this and next week that uses the tested PID and PWM classes instead of a hack. Therefore I have decided not to fix the bug in the code that will be discarded.

You can switch to the stable release by running flashDfu again, but all settings will be erased, so you will have to set up your devices again.

molc · October 30, 2015, 9:56am

Just checking how this new release is going. I’ve been watching the github, but it doesn’t really give an indication of how close you are to the official pwm release at this point. Dying to try it out.

Elco · October 31, 2015, 8:41am

I expect to test mashing with the PWM code this week. That is without a nice UI for it, but all the control code is there.
A release before the end of the November.

nickhegge · November 15, 2015, 4:17pm

Hi @Elco

I have been using the preliminary release and am not to familiar with PID tuning (tried to use your earlier post advice on Aug 8th with limited success). The last couple of mashes I have done using the latest have overshot the temp and have taken a long time to level out (30min+). I have tried one batch where I let it get up to temp and then turn it off and restart the temp set point. That experience it allowed the temp to drop significantly and would not get back up to the desired temp for the rest of the mash.

Should I just leave the settings you have in their at default or is there a better tuning you have found? Or… does the new update that you mentioned being released before the end of Nov make doing step mashes easier and address this issue.

I am running a single 120v rims system in a 15 gal mash tun with a false bottom. Here is a video of the system in operation.

Thanks for continuing to push this project forward!

Nick

Dan · November 15, 2015, 9:12pm

It was my understanding that the preliminary release was only proportion PWM control and not full PID. I might be wrong.

molc · November 17, 2015, 9:46am

Hi,
Just a quick use case for the release. When using mash control, there will be a different set of temperature probes to when doing fermentation. It would be great to be able to give these device id’s and permanently associate them with a mash activity, similar to how there is beer1 and chamber right now.

Alternatively, if we can import/export device settings from a json backup file, we can make different configurations and just load them as necessary, though this requires more GUI work I’m assuming.

Yet another alternative is if you can give us something in the command line that we can run to backup the settings ourselves and we can swap between the configurations ourselves manually.

Finally, how do you feel the development going for the release at the end of the month? In the absence of a development blog, this might be a nice way to get a quick update on progress up to keep the fans quiet

Elco · November 17, 2015, 10:53pm

The new release will be implemented completely different from this temporary PWM release. I do not recommend using this.

@molc: yes that was my plan, a quick dump and reload of settings to switch between fermentation and mashing config.

Borisfa · April 6, 2017, 10:55am

@Elco, my doubt is related how to implement control action translating PID control action to analogWrite value (duty cycle). Seems logic that duty cycle is proportional to error between setpoint and PV, but how to translate it, linearly? Linearly considering what limits (upper and lower)? How is implemented the logic to translate PID control action to 0-255 argument in analogWrite to change the duty cycle?

Thanks,

Fabiano da Mata

Elco · April 6, 2017, 11:30am

This has been implemented in the BrewPi Spark. Not with analogwrite, because that PWM cycle is too fast to work well with a 50Hz AC signal. We wrote our custom, much more advanced PWM algorithm that can take into account time limits and mutual exclusivity of actuators.

We have not build this for Arduino and never will. If you want to do it yourself, that’s fine, but we have abandoned Arduino as a platform.

Borisfa · April 6, 2017, 11:50am

Ok @Elco. The Spark PWM code is available? Could you tell me where can I find it? The Spark PID is a PID tradictional, or is it modified also?

Thanks,

Fabiano da Mata

Elco · April 6, 2017, 12:32pm

The PID is new and the PWM class depends on multiple other classes that are new in the Spark firmware.

github.com

BrewPi/firmware/blob/master/lib/inc/Pid.h

/*
 * Copyright 2015 BrewPi / Elco Jacobs
 *
 * This file is part of BrewPi.
 *
 * BrewPi is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * BrewPi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with BrewPi.  If not, see <http://www.gnu.org/licenses/>.
 */

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github.com

BrewPi/firmware/blob/master/lib/src/Pid.cpp

/*
 * Copyright 2015 BrewPi / Elco Jacobs
 *
 * This file is part of BrewPi.
 *
 * BrewPi is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * BrewPi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with BrewPi.  If not, see <http://www.gnu.org/licenses/>.
 */

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github.com

BrewPi/firmware/blob/master/lib/inc/ActuatorPwm.h

/*
 * Copyright 2015 BrewPi/Elco Jacobs.
 * Copyright 2015 Matthew McGowan
 *
 * This file is part of BrewPi.
 *
 * BrewPi is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * BrewPi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with BrewPi.  If not, see <http://www.gnu.org/licenses/>.
 */

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github.com

BrewPi/firmware/blob/master/lib/src/ActuatorPwm.cpp

#include <stdint.h>
#include "ActuatorInterfaces.h"
#include "ActuatorPwm.h"
#include "Ticks.h"
#include "ActuatorMutexDriver.h"

ActuatorPwm::ActuatorPwm(ActuatorDigital & _target, uint16_t _period) :
    target(_target),
    dutySetting(0.0),
    dutyLate(0),
    periodLate(0),
    minVal(0.0),
    maxVal(100.0)
{
    target.setActive(false);
    setPeriod(_period); // sets period_ms
    periodStartTime = ticks.millis();
    // at init, pretend last high period was tiny spike in the past
    lowToHighTime = periodStartTime - period_ms;
    highToLowTime = lowToHighTime + 2;

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This will be hard to migrate to the Arduino.