Hottop Manual Roast Controls (for Digital Model)

[yoma]

This is a cheap and relatively simple modification I made to provide 2 dials to manually control the heater and rear fan.

Connector 1 on the hottop controller board has 5 control lines to - the rear fan, eject chute, cooling tray/fan, drum and heater - via the main board. I (carefully) removed the rear fan, and heater lines (pins 3 and 7) from the controller board connector which I connected to my own circuit. I also tapped (soldered) into the 0V/5V power lines (pins 1 and 2) via the same connector.

My circuit comprises two 555 timer based multivibrators - one to drive the heater, the other the rear fan. The specific Extended duty cycle astable circuit used is from http://www.doctronics.co.uk/555.htm#more%20astables, the only minor difference the addition of the potentiometers (dials).

Heater Circuit
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R1=R2=1k, C=330uF, POT=100k
This gives mark space periods b/w 0.2 and 23 secs.

This means every 23.2 the heater is switched on/off once depending on the dial setting. Max. power is on/off 23/0.2 sec. 75% power is on/off 17.4/5.8 sec, etc.

Rear Fan Circuit
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R1=R2=1k C=2.2uF, POT=10k
Mark space periods -> 16.7msec, 1.5 msec

Circuit details
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Ill post the specific circuit I used soon...
Also it wouldnt be difficult to add in a couple of switches to allow control of the heater/rear fan to be switch to/from the hottop (I didnt have any handy at the time + plus I was too lazy to do the extra wiring).


Fine Tuning
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After 3 roasts, I found the heater has quite a bit of inertia - takes a while to heat up / cool down so Ill probably try a short mark space of about 15sec. Ill probably revise the fan to have a minimum duty cycle of around 1% from 10% - its too easy to spin.

DISCLAIMER
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This site or myself shall not be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with use of or reliance of this information.

[Wushoes]

Re: Hottop Manual Roast Controls (for Digital Mode

I love the ingenuity of people. Hope it works well!

[Andy]

Re: Hottop Manual Roast Controls (for Digital Mode

Very nice tinker Yoma, Ill watch with interest and when you think its out of "alpha version" Ill have a crack at it too.

Look forward to reading more.

[Mocha_Zarba]

Re: Hottop Manual Roast Controls (for Digital Mode

Nice job Yoma,

Being in the electrical game myself, I can appreciate what you have done. The 555 timer is one of the most versatile devices ever invented, long live the 555 timer !! ;D


MZ

[yoma]

Re: Hottop Manual Roast Controls (for Digital Mode

I love the ingenuity of people. Hope it works well!

Thank you.

I can push through around 200+ grams of coffee to 1st crack in about 9:00min. (I could do this on the unmodified hottop, but jumping through hoops to get there).

I then turn down the heat as it heads toward the 1st crack - and try to ease it through for another 5 mins. This is next to impossible on an unmodified hottop.

The inspiration came from a 1 in 150 hottop roast (red sea blend) with a similar profile to the above. It was by far the best roast Ive done - actually best roast Ive had anywhere.

Anyhow, manually controlling the temp. during the critical end stages of the roast takes a bit of practice - and thats using my own temperature probe to help. Once I work it out Ill prepare a time-based guide.

[gregpullman]

Re: Hottop Manual Roast Controls (for Digital Mode

Nice work indeed. So this basically makes it a Hottop with the flexibility of the Gene?

[yoma]

Re: Hottop Manual Roast Controls (for Digital Mode

Im not sure about the details of the Gene.

I push through roasts between 12min to 13min.
Around 9min to FC.  Thats for 220g to 225g green.

Having the manual control makes all the difference.  For example...
Ethiopian - I pull the heat back to 60% at FC then up to 100% end of FC.
Sulawesi - I pull the heat back to 75%, then use the fan just before SC.

Ive found its just not as good for 250g.  The couple of min. extra in the roaster kills off some body and sweetness.  Uping the heating capacity to around 900W/1000W would probably do the trick.

[gregpullman]

Re: Hottop Manual Roast Controls (for Digital Mode

Nice work. I think the Gene has a 1000W heater element so thats probably something its got going for it. I used to design 555 timer circuits in my sleep (almost) but if you can save us the bother and me dusting off cobwebs and post the circuit diag itd be great, thanks!

Greg

[JavaB]

Re: Hottop Manual Roast Controls (for Digital Mode

Greg,

The Hottop has the power control circuit on the main board so it just needs a variable pulse width to switch it and vary the heater power.....

With the gene that may not be possible.... unless it has a mainboard the same as the HT - designed for pulse width modulation - it is quite possibly only an on/off control from the thermostat.... where as the HT heater is under control of the microprocessor (crude) PID..... and so responds to digital (low voltage) levels.

[gregpullman]

Re: Hottop Manual Roast Controls (for Digital Mode

http://www.roastmasters.com/hottop.html lists the Hottops element as being a 750W unit whereas the Gene has a 1000W element. 750 doesnt seem much considering what its trying to do. This is odd since the Gene has more plastic than the Hottop (apparently) so I wonder if the Hottop could take a more powerful element, supply permitting? Itd be interesting to know how hard the Hottops element is actually getting driven (I think you said something about it having some spare capacity?).

My Gene roast suggests its definitely an on/off setup - the first tick of its thermostat I thought it was the start of FC! ;D From there on it was oscillating up and down with about 2dec C variation as the thermostat clicked in and out. So perhaps more judicious use of the available power (via PWM) could allow for more efficiency than a all-or-nothing setup like the Gene; though one comment about the Hottop seems to be that its roasts are longer which would correlate with a weaker heater element.

Greg

[JavaB]

Re: Hottop Manual Roast Controls (for Digital Mode

Yep, the HT element is 750W and after pre-heat (heater on at 100% until that point) - it seems to be cut back to about 50-60% for the rest of the roast.... hence the longer roast time....

But either with yomas mod or a PID - that could be increased to 100% when required - thereby shortening the roast time.

The big difference between the heat requirements IMHO is that the Gene heats the air - and looses a lot of that heat by exhausting the hot air out of the chamber - only transferring some of the heat to the beans.....

With the HT there is no air movement until the start of FC (the fan cuts in briefly at about 100C - presumably to remove the steam).... so all heat in the chamber stays in the chamber except for a little convected and radiated loss into the atmosphere..... This would appear to be a far more efficient process - therefore a 750W heater is more than adequate especially when you consider they are trying to emulate a drum roaster with a roast time of about 20 minutes.... and they can do that with 60% power to the heater.

I doubt a more powerful heater is actually required with this design.

[gregpullman]

Re: Hottop Manual Roast Controls (for Digital Mode

Good reasoning JavaB, I guess another alternative would be the B upgrade though its approaching half the cost of the Gene at $US300! Why do they make those things so expensive??

[JavaB]

Re: Hottop Manual Roast Controls (for Digital Mode

I guess another alternative would be the B upgrade though its approaching half the cost of the Gene at $US300! Why do they make those things so expensive??

Yep, it is expensive - however it replaces both the simple digital control mainboard and the control panel with what amounts to a couple of interlocked PIDs and SSRs so that you have far better control of all functions. The existing D version is a PWM system of control rather than the almost linear control of temperature and fan speed possible under program control with both the B and especially P variants...

Or you can just fit a ramp/soak PID

[yoma]

Re: Hottop Manual Roast Controls (for Digital Mode

AFAIK, the newer hottop controller(s) still use their next to meaningless temperature sensor which defeats the purpose of all that high priced stuff behind it... garbage in -> garbage out.

The chamber sensor as they refer to it has no bearing to the temperature of the beans.

Id like someone to tell me this is no longer case, because in my experience - the hottop components can easily produce consistently excellent coffee.

[JavaB]

Re: Hottop Manual Roast Controls (for Digital Mode

Yoma,

Im sure you are right.... it uses the same "environmental" RTD in all versions.

IMHO that is probably one of the most significant weaknesses of the HT (and the Gene....) they both measure the chamber temperature (or air temp).... which doesnt reflect the actual bean temperature.

Surprisingly (using a thermocouple actually in the bean mass).... the HTs indicated temperature is within about a degree from FC to SC.... but before FC it is 10C - or more - higher than bean temperature....

Even a degree is too much.... and a bean mass probe is the only way to go - and dead easy (with the HT) to install one - as long as you are prepared to drill a couple of holes in the stainless steel...... definitely worth the effort!!