MAX31855 based reflow oven controller

[yyrkoon 250]

First, Much thanks to Rickta59 for helping me understand various aspects of the MSP430 in hardware, and software. Then to Spirilis who wrote the SPI initialization, and usage code in an attempt to help me understand HW SPI better. It worked Also to the many others who have helped me on these forums. 

 

I need to mention this project is still in design phase. PCB layout is nearing final stages. Layout / schematics design is done in OrCAD, and as I've been informed most ( or all ? ) everyone here uses EagleCAD. Sorry, but nothing I can do about that, and have been unsuccessful, in finding any reasonably priced conversion tools. In the end the layout software used is not up to me. 

 

I do not know how many would be interested in a PCB, but the board will be usable as a stand alone board, or as a boosterpack. Everything as I understand it part wise should be thru-hole, for easy hand soldering.  But depending on how many people would like one, price per would be around $5 each, plus shipping from us to you. USPS should be around $2 - $3, US only. Anyway, not looking to make anything here, just looking to lower costs per person( including ourselves ). 

 

below is a PDF attachment of the schematic for those who wish to view it.

 

EDIT:

 

Also I am ( and have been ) writing the software "library" for this board as we speak. The idea is to use an LCD, a couple of buttons for menu selection, then optional fan, and buzzer. So far I have a table driven "state machine" implemented in code, with initialization for UART ( debugging using printf(), but can leave this in too ), Minimal SPI communications, and have the code reading values out of the MAX31855, and displaying them out over UART -> serial printing various information. Again, the UART -> serial functionality is meant for debugging, but could be left in as the code will likely never even reach 8kb in total.

 

Anyways questions are welcome, if there are any to be had.

 

EDIT:

 

reflow.zip uploaded for use with these reflow oven boards.

SCHEMATIC1 _ PAGE1.pdf

reflow.zip

[jsolarski 94]

Is it possible to replace the SSR (MOC3069) with relays With the software you are making for it?

 

(I know a few changes would have to be made for the driving the relays)

[yyrkoon 250]

Is it possible to replace the SSR (MOC3069) with relays With the software you are making for it?

 

(I know a few changes would have to be made for the driving the relays)

 

 

Not exactly sure of the hardware implications, wulfman( my friend and EE behind this project ) says relays make noise and fail, cost more, and are larger. TRIACs on the other hand are zero crossing, keeping surges from happening.

 

As far as the software goes, for now I just plan on switching on/off based on a tested threshold. But did consider ( later ) testing PWM to help curb heat spikes / lag.

[yyrkoon 250]

Software so far initializes SPI, UART, and the max device. Asks the user to press a key ( serial terminal ), then based on table values starts counting down from the duration entry to 0. For each stage. All the while displaying formatted data over serial UART to the PC.

 

Things yet to implement:

 

LCD initialization / usage

button trap detection

heating elements toggling code 

fan toggling

LED toggling

temperature comparison ( probe temp vs target temp, and controller temp vs a  shutdown threshold ).

 

Example of formatted test output over UART-> Serial thus far.

 

[jsolarski 94]

Not exactly sure of the hardware implications, wulfman( my friend and EE behind this project ) says relays make noise and fail, cost more, and are larger. TRIACs on the other hand are zero crossing, keeping surges from happening.

 

Relays do make noise and do fail, but all components fail, its not if, but when. 

As for reliability, Relays are still used very comonly in Dryers, washers, and dishwashers, and have a reliability of years if not decades with out fault, and I am pretty sure I have seen some in electric stoves as well.

 

So I think it will work, if you use the on off method, but not for PWM unless you use a secondary driver for PWM.

 

 

for the cost issue? SSR/TRIACS VS relay, I have seen ridiculous prices for SSR/TRIACS and for relays......So it is application specific for cost in my opinion.

[wulfman 17]

BTA26-800BWRG triac = $3.20 each                                     this will easily handle the heater current

MOC3063S-TA1 zero crossing triac driver  - 47 cents each   3.3 volt turn on makes a smooth turn on turn off for the triac

triac needs a heatsink which is a piece of aluminum that all triacs share maybe a buck for it

 

 

SP2-L2-CD3V   = $32.00     15 amp relay 3 volt coil  requires a transistor to drive the coil from a msp430

requires no heatsink uses more board area

 

AQA331VL = 25 bucks  15 amp ssr triac output needs to be mounted to something for heatsinking  needs a transistor

to turn it on from a msp430 very large and bulky

 

 

For the oven you need 3 of the relays, triacs-drivers or SSR  to control the functions.

True the fan driver can be less current and use a cheaper relay or ssr.

 

But for over all cost savings the triac beats the other solution hands down

 

 

Also i am using a cheapo chinese wall wart for the 5 volts i remove the small board from the wall wart and glue it to the board

with silicon. you cant even buy a flyback transformer for the cost of the whole wallwart from china

 

I have seen cheaper relays and ssr's on ebay but they are not consistent in availability.

You cannot design for manufacturing using ebay.

All my parts can be purchased at mouser.com for ease of purchasing.

 

Keep up the comments.

 

Wulfman.

 

[yyrkoon 250]

@jsolarski, You should be able to use whatever you want, to drive the heating elements in the toaster/convection oven of your choice. 

 

Whatever the case, I made this post primarily to see if anyone else wanted a PCB, so we could see if ordering more than 5 boards would be worth it to us. That means, we're not going to order more boards, unless others want / can use them too. We will not be making any profit from this, but definitely will not take a loss either.  

[jsolarski 94]

@yyrkoon

I see, I am just asking questions, since I am interested in different ways to convert my toaster oven.

And your design I like, So I am just curious on other adaptations that use your software but not neccasarily your specific hardware design.

 

 @wulfman lol ebay would be the worst way to try and design a manufactured board, but for one offs and prototypes it works in a pinch.

                     AS you do break down the cost, the triacs in this application you are probably right, that you will not find something cheaper.

 

 

 

Keep up the good work, looking forward to your results of the fniished product.

Thanks for the great info

 

I may be interested in a board to play around with. So at least you have one person for a PCB

[yyrkoon 250]

At this point I am kind of stuck waiting for a PCBA. I could write in the LCD stuff and test, but the rest requires the real deal. This way I can write code and test as I go( which makes debugging much simpler / easier / faster ) 

 

Anyone else would like a PCB ?

[RichardVowles 12]

I would!

[yyrkoon 250]

Richard, sorry but shipping to anywhere out side of the US  is not something we're willing to deal with. Plus shipping costs would likely make it very unattractive for you.

 

The design is there in schematics though, feel free to layout it out in whatever app you prefer to choose. Consider it open source hardware. Then use my firmware library freely as well. When I make the firmware available. 

 

Richard, actually wulf just told me he is willing to give it a try, but that you would have to pay the extra shipping. 

[wulfman 17]

I will ship bare boards to anywhere. postage will be determined when i get an address customs forms are not too bad here

 

i have a few more boards to finish up and then i will submit a batch order so i get free shipping

[jpnorair 340]

Wow... I go away for a few days, and then this.  What are you asking for the boards?  I'm interested.

 

Also, while you will certainly want to maintain your AC phase for the fan controller, it is probably overkill for the heater elements.  For those, I don't think phase matters -- but I could be missing something.  Sometimes there are back EMF considerations that are dependent on hard-to-predict factors.  An experienced AC-power engineer will know these things.  I am an RF and signals engineer, which isn't a world apart, but magnetic inductance into control circuit elements is almost never a problem in my line of work.

 

Lastly, if you wanted to take this project to the next step, you could implement a zero-crossing detector using the MSP430's comparator circuit, and in-turn use that to drive a MOSFET, thus removing the MOC3063's all together.  G2553 may not have the COMP module, though.  The awesomely-priced 5510 board for sale on 43oh.com does, however.

[yyrkoon 250]

jpnorair, really depends on how many join in, but around $5 for a bare board, plus ~$2-$3 USPS shipping. We're not looking to make anything, just trying to minimize costs for everyone including ourselves.

 

As for the EE technicalities, I let wulf handle that as he has 30+ years experience. I will say however, just because something is on the board does not necessarily mean you have to "populate" it. Just like it probably will not be necessary to use a second thermocouple, but the option will be there if you choose to do so later.

[wulfman 17]

You cant drive a triac with the msp430 directly you need something that triggers using the 3v/0v it provides

 

also you need a way to isolate the AC mains from the rest of the board which the triac driver does with its built in opto isolator.

 

Cant think of anything else better for the job than the 43 cent  triac driver. Zero crossing is the preferred way to drive resistive loads

 

when on an inverter which i am. I run my home and development lab on solar power. If anybody can think of a cheaper way to drive

 

the heating elements please let me know.