USB Hot Top Teaser

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USB Hot Top Teaser

Postby mnemonix » Sun Aug 24, 2008 3:18 pm

Nearly 4 years after my first, rather excitable, article on computer controlled popper roasting for TMC, the lights are burning late at the lab again and the development of hardware & roasting software for a USB/laptop controlled Hot Top is progressing nicely.

Whilst I'm doing this primarily for personal use, I'm curious as to peoples thoughts and interest in the project as they may well help shape the final implementation.

Cheers!

Chris
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Postby JonS » Sun Aug 24, 2008 3:42 pm

Chris,

I've thought about this on and off myself this year, since getting back into roasting again with my hottop.

Control of the hottie seems pretty straightforward from what I looked at, but I'd be most interested in what your thoughts are regarding actually measuring the temperature - the hottie's sensor seems of little use either as an environmental or "bean" temperature sensor when it comes to achieving the best control over the roast profile.

I've recently fitted a bean mass probe to my HotTop programmable, but I think a better environmental sensor would be of use as well.

Jon
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Postby mnemonix » Sun Aug 24, 2008 4:00 pm

Hi Jon,

I currently have provision for and anticipated measuring both bean & environmental temperature.

Whilst I avoided going into too much depth in the first post, this question, and I suspect most others all point to an implementation issue with which I'm grappling. I'm sure a plug-in replacement for the HT control panel would be popular, but to be truly plug & play it would likely not allow for the fitting of additional sensors or other modifications. It may also be hamstrung by the limitations of the Hot Tops own electronics, though I haven't gone far enough down the reverse engineering route to know this for sure yet.

From a personal point of view, it makes most sense to rip out the Hot Top's electronics and replace them, in which case other modifications such as the addition of temperature sensors is trivial for me at least. As I said, this is primarily a personal use project so it need not be an issue, but I'm open to possibilities should the potential & necessary solutions present themselves.

Chris
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Postby CakeBoy » Sun Aug 24, 2008 4:21 pm

Hi Chris. I'm also hugely interested in your project. The idea of computer control and profiling in home-roasting is very exciting to us regardless of whether you take the add-on or electronics rebuild route :)
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Postby JonS » Sun Aug 24, 2008 4:24 pm

Hi Chris,

You are right that because of the lack of really useful sensors, a truly plug n play solution is difficult. You could achieve the same level of control as the HotTop "P" programmable model but do it via USB and a computer, if you reverse-engineered the resistance/temperature curve of their sensor. But if very accurately repeatable roasts matter more than plug and play, then I think adding the sensors is preferable. FWIW, probably the main reason I haven't yet gotten around to taking my own control ideas further, is that I thought that a plug n play replacement control board using the internal sensor would be the most universally useful approach to take. If you want to build a truly great roaster, I no longer believe this is the case.

Other than that, the control of the HotTops internal control board from 5v logic is simple, I know that much as I looked at that board in some detail. As that part doesn't relate to temperature reading at all, it could maybe be worth keeping it. I think the multi-pin connector is a little difficult to come by though, or at least was the last time I looked.

The "P" (and "B") model hottops add an extra control wire to the analogue board over the original ones, an interrupt pin. I haven't looked at this board in any more detail, but I believe this could be used for more accurate timing, true zero cross switching of the heater, or even phase angle modulation rather than PWM control of the heater for more precision and response.

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Postby mnemonix » Sun Aug 24, 2008 4:39 pm

The only solution to adding probes with a plug and play solution that I've come up with so far, would be a modified bean shute cover with 2 probes mounted to give the appropriate extension into the drum to measure bean & environment temperature. These could plug into the front of the control panel for easy assembly.

Re the heater control, although I used pwm for the popper I was considering a Diac/Triac solution this time. The machine is rated at 750W so the heater will be a little less than this and not beyond a reasonable implementation, unless your experience suggests otherwise ? <edit> this precludes the plug and play solution again though obviously!

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Postby JonS » Sun Aug 24, 2008 4:50 pm

Re the heater control, although I used pwm for the popper I was considering a Diac/Triac solution this time. The machine is rated at 750W so the heater will be a little less than this and not beyond a reasonable implementation, unless your experience suggests otherwise ?


When you say "Triac" but not PWM, are you thinking then of Phase Angle modulation like a light dimmer, where you detect the zero cross, and then delay turning on the output to use only part of the wave ? Or am I misunderstanding ? The original board uses a BTA16 triac for heater control with a MOC3023 isolator / driver. I'd have thought a similar setup would work fine for PWM or Phase angle control, assuming you do the zero cross detect.

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Postby JonS » Sun Aug 24, 2008 4:56 pm

As an aside, if you don't already have the control details for the internal board (just for reference, really, I'm not trying to persuade you to use it)

from the outer edge of the board inwards:

GND / 0V
+5V
FAN (both drum and cooling fans, PWM control on newer models)
EJECT SOLENOID
MOTOR2 / AGITATION
MOTOR1 / DRUM
HEATER (PWM control, or maybe phase angle on the newer models)
INTERRUPT ("P" / "B" models only, pin not present on older models)

These are all 0v/5v based logic signals

After I'd worked all this out by looking over my old control board when I did the "P" upgrade, I found this page which goes into some further detail.
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Postby mnemonix » Sun Aug 24, 2008 5:04 pm

Ah... yes, sorry a combination of me re-inventing the wheel and not being an electronics engineer. As I said, I hadn't reverse engineered the Hot Top and started from the point of view of replacing everything - in the case of the heater control, with a dimmer-like circuit. PWM to me is simply switching something on and off, which I did with the popper before I'd heard the term, PAM is new to me and while I'm not familiar with the theory I can certainly implement a device to do the job!

From what you say, it seems that a plug and play solution might not be as difficult as I'd assumed. The 5V logic control is trivial and if the secondary board in the Hot Top has nothing to do with the profiling but merely responds to triggers from the control panel to activate motor, heater, fan, bean dump solenoid etc then it might be worth considering.
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Postby mnemonix » Sun Aug 24, 2008 5:10 pm

JonS wrote:As an aside, if you don't already have the control details for the internal board (just for reference, really, I'm not trying to persuade you to use it)

from the outer edge of the board inwards:

GND / 0V
+5V
FAN (both drum and cooling fans, PWM control on newer models)
EJECT SOLENOID
MOTOR2 / AGITATION
MOTOR1 / DRUM
HEATER (PWM control, or maybe phase angle on the newer models)
INTERRUPT ("P" / "B" models only, pin not present on older models)

These are all 0v/5v based logic signals

After I'd worked all this out by looking over my old control board when I did the "P" upgrade, I found this page which goes into some further detail.


Great stuff... in fact this suggests overkill on my part as i was essentially just replicating this functionality with additional circuitry on top of the 5V logic control.

The result is a very different project, I've always had in mind the idea of an interface that could be used with different roasters whereas this would be very much Hot Top specific, but until I can afford a Probatino, that's not necessarily a problem!

Chris
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Postby mnemonix » Sun Aug 24, 2008 5:31 pm

CakeBoy wrote:Hi Chris. I'm also hugely interested in your project. The idea of computer control and profiling in home-roasting is very exciting to us regardless of whether you take the add-on or electronics rebuild route :)


Well the advent of cheap USB interfaces since I wrote the original article means that a computer controlled popper or a USB Hot Top panel can be built for less than £50 now (and the parts themselves cost literally pennies), which certainly puts Hot Top's pricing in perspective! For a company though, development time is what costs, and DIY requires quite a collection of skills from programming to electronics, though none of it is terribly complicated.
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Postby JonS » Sun Aug 24, 2008 7:27 pm

mnemonix wrote:As I said, I hadn't reverse engineered the Hot Top and started from the point of view of replacing everything - in the case of the heater control, with a dimmer-like circuit. PWM to me is simply switching something on and off, which I did with the popper before I'd heard the term, PAM is new to me and while I'm not familiar with the theory I can certainly implement a device to do the job!


I've heard the terms Phase Angle Control and Phase Angle Modulation used somewhat interchangeably to be honest. There are articles here and also here (amongst others) that talk a bit about it.

I don't know exactly how you did PWM with the popper, but the general idea would be to vary the on and off times (vary the duty cycle) within a fixed total period to approximate an average power level.

Power control via phase angle control feels like it should have some advantages, and power is potentially always being applied to the heater, so you'd think there'd be less thermal inertia.

Anyway, really excited to know that you're tackling this project 8)
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Postby mnemonix » Sun Aug 24, 2008 8:17 pm

JonS wrote:I don't know exactly how you did PWM with the popper, but the general idea would be to vary the on and off times (vary the duty cycle) within a fixed total period to approximate an average power level.


Exactly... I took my first few days roasting experience of turning the popper on and off by hand to control the roast and used the computer to do it with a mechanical relay varying the duty cycle within a 1 second period. 1 Hz pwm ! It wasn't hi tech, but I was making this stuff up as I went along ;)

This project thankfully will be considerably more sophisticated, but it's worth considering which aspects of the process benefit from high levels of precision. Thermal momentum (I assume there is such a term) of the system & its components suggest to me for example that beyond a certain level, the bean simply won't see further refinements to the heater control. I *do* want the best result however, it's a case of deciding where best to focus ones efforts.

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Postby zix » Sun Aug 24, 2008 8:44 pm

Peoples thoughts and interest in the project

I've always had in mind the idea of an interface that could be used with different roasters whereas this would be very much Hot Top specific

You making a USB controller for a roaster - yes, very interesting. For the HotTop per se - well... I think it might be even more interesting with a general roast profiler, something that could be used for many different roaster types.
Also, I might add a slight preference for the PWM method, as there is quite a bit of effect to dim here. Besides the problem of obtaining high effect dimmers (with triacs and such) that can switch >1.5 kW, modulating the sine wave like dimmers do (by cutting it off) is known to pollute the grid, sending the switching noise back into the wall outlet and to surroundings. Radios nearby, and often amplifiers too, pick it up. Don't like it.
On the other hand, a "slow" PWM circuit, with, say, a 0.5 or 1 second base period, should get rid of all that potential noise, even at high effects. I have such a controller at home, haven't used it for anything yet but it is a very simple looking control. Looks and function of a smallish potentiometer, turn the knob and you get more effect through it. Only it switches up to 2.5 kW without a problem, 1 second intervals. You would need something without a knob that needs to be turned to the right position though.

I will follow this closely, no matter which road you choose. Most interesting!
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Postby JonS » Sun Aug 24, 2008 9:33 pm

Zix I was somewhat aware of the potential for interference, that might well be an issue. Though the load we're talking about is < 800W and mainly resistive, so it may be quite a bit less than the worse case. I need to do some more reading on the subject really, I'm no expert.

PWM will certainly be easier to implement in the first instance, given the "standard" hottop electronics because they lack the zero crossing detection required for phase control. Well, actually, there is some provision on the board, but it's not connected. If interference is an issue, then ideally zero crossing detection would be useful to switch the PWM on the zero cross, but certainly the original hottop doesn't do this.
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