Overview

User Interface

User interface is provided by the LCD and four leds.

Leds, from left to right:

Orange Mostly red when on. Power on, shows that the board is powered.
Blue Status Led. Used for various pourposes, it is usually on when there are problems with temperatures and when a reflow process is running.
Green On when FAN CTRL is on
Dark Orange On when HEATERS CTRL is on

 

x-toaster-leds
Please note that all the leds has been polarized to have mostly the same light intensity except for the SSR HEATER which is a little bit brighter (electricity is flowing, heat is generated)

On the LCD you can navigate through the menu with the touchscreen:

 

Main Menu

From here you can check the oven’s temperature as read from the thermocouple, the onboard temperature sensor readings and how much time passed since the board was powered.
Three red buttons on the left will start the respective reflow sessions, while three blue buttons on the right allows the user to reprogram the profiles with their names and their advanced parameters.
The purple button will allow to change general system settings and the grey one is used to overview some system info and all three temperature sensors.

 

Setup Reflow Profile

Each profile has five time nodes arranged in this way (t0 is the moment in which the reflow profile is started, for t0 temperature is automatically read from the oven):
t0-t1:  PREHEAT PHASE
t1-t2:  SOAK PHASE
t2-t3:  RAMP-UP PHASE
t3-t4:  REFLOW PHASE
t4-t5:  COOLDOWN PHASE

Each of these five nodes can be programmed with the desired time/temperature and for each of these phases you can sepcify if the oven’s fan has to be turned ON or OFF.
You can move between the options using the “PREV” and “NEXT” buttons, values are changed with the “+” and “-“ buttons.
The graph drawn on the top-left corner shows a visual preview of the profile you are programming and is refreshed whenever a change is made or when you touch it.
When you are satisfied with your profile you can save it to EEPROM by pressing the “SAVE” button which will bring you back to the main menu or you can press the “ADVANCED” button to save it and enter another page in which you can modify the advanced parameters for that profile.

 

Advanced Reflow Parameters

Preheat Until

Used to keep the oven ON from the start of the reflow session, discarding any PID result, until a certain temperature is reached. This may be useful to avoid big Ki summing due to starting inertia and to speed up initial heating. When set to 0 this control is disabled.

Fixed RampUp

Like the “Preheat Until” parameter this control allows to keep the oven ON during the RAMP UP phase but, instead of a temperature you can specify for how many seconds you want to discard PID results. This may be useful if you needed to use big Kd values to limit overshoots but you need to quickly heat up the oven to reach reflow temperature. This control is disabled when set to 0.

Ki limit factor

This parameters starts acting when there are overshoots, lowering Ki at a faster rate than normal. Disabled when set to 0.

Smooth Radius

Since your reflow curve is going to be 5 segments delimited by the nodes, the “steepness” of the knees may result in overshoot and/or undershoot. This parameter helps in smoothing your profile by drawing another segment which replaces the knees around the nodes for the programmed seconds. When set to 0 this control is disabled.

Previsioning

A big problem with toaster ovens is their large thermal inertia which leads to time lags of the output. If you can observe this kind of behavior by changing this parameter you can effectively shift your real observed curve ahead or later in time in respect to the target ideal profile. For larger oven this parameter give good result with values of 10~18, smaller oven having lower inertia may be ok with a value of 2~10. A little bit of testing is necessary to fine tune it. This control is disabled when set to 0.

Overshoot Compensation

Like the Previsioning Parameter, Overshoot Compensation allows to compensate for thermal inertia in the REFLOW PHASE where usually there is a target temperature to keep and maintain for a given time. This problem is also known as Thermal Hysteresis: your profile is almost perfect but when it has to settle at a temperature it constantly overshot by a few degrees. Set this parameters exactly equal to the overshoot you are observing to compensate for it. This parameter is disabled if set to 0.

PID-Kp

The proportional constant of the PID controller

PID-Ki

The integral constant of the PID controller

PID-Kd

The derivative constant of the PID controller

 

System Settings

DEFAULT SETTINGS – Restore all system preferences to defaults
DEFAULT PROFILES – Restore all profiles nodes and parameters to defaults

These are the parameters you can customize in the System Settings Page:

Timeout

How many minutes before the system enters standby/shutdown and the user is asked to take actions

Int Sen MAX T

Maximum temperature reading allowed from the onboard sensor before firing a Temperature Alarm and the user is askedto take actions.

Ext Sen MAX T

Same as Internal, but for the external sensor

Oven MAX T

Same as onboard and external sensor but related to temperature read from the thermocouple.

Buzzer Volume

increase or decrease buzzer volume

Offset Temperature

Thermocouple reading error is not linear over the entire temperature range, but if you can observe a fixed offset in respect to other sensors you can adjust it from here. It can be set both with negative or positive values.

Draw Real Curves

If, during reflow sessions, you want to display both the ideal curve (only defined by nodes), and the ideal curve modified by advanced parameters (except previsioning), by setting this value to YES you will see the ideal green curve, a modified yellow curve and the real measured values in red.

 

System Info

The "System Info" page will show you some information about the connected DS18BXX sensors and the stored parameters for the touch screen calibration.
By pressing the "Recalibrate" button you will enter a page with a 5 points recalibration routine.

If, for some reason, you mess up with the recalibration parameters and you are no longer able to enter this page you can shut down the board, touch the screen and keep pressing while the controller is powered up. It will automatically enter the recalibration page.

 

Start Reflow

Reflow page is mostly occupied by the time/temperature graph in which you can confront the target ideal temperature (green) and the measured temperature from the thermocouple (red).
You can also check the numerical values in the bottom left of the screen where in green you can read the ideal target temperature (calculated against the advanced parameters) and in red the measured temperature.
The second grey square at the bottom left shows the internal and external temperature sensors values.
On the third grey square, as a reference, saved PID constant are shown.
The bigger red square stops the reflow process if needed.
On the top left you can read the custom profile name, in the center the calculated PID parameter and at right time in seconds from the start of the process.
Calculated PID values are a must when tuning your controller: by visualizing them you can see which one needs to be lowered or increased.
During COOLDOWN phase the controller will ask to open the oven’s door.

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X-toaster Board Layout

 

RESET Reset for the Xmega, not mounted.
PDI Programmer/debugger interface for the Xmega, if you have one of the latest PDI capable Atmel programmer like the AVRISPmkII and the ATMEL-ICE you can use it to upgrade X-toaster with future firmware revisions.
INT SENSOR Populated with a DS18B20+, used to read the temperature around the board.
If you are going to fit X-toaster in an hot environment (like inside the oven itself) it can be used to keep track of the temperature and shut the system down if temperature goes above some limit that you can program via GUI.
EXT SENSOR  Unpopulated. You can fit another DS18B20+ to read temperature from another area. Like the internal sensor it possible to set a maximum temperature after which the system has to be shut down. If you mount the controller in a separate box but if you fit the SSR inside the oven, you can use it to make sure that the SSR is not overheating.
G: ground, V: 3.3V, D: data
HEATERS CTRL  This is used to drive the SSR which controls the oven’s heaters.
Its output is a slow PWM with a peak voltage equals to VIN less voltage drops on D3 and Q4 which results in around 4.70V. Some Chinese SSR are not able to fully turn on and work properly even if they have 3V~32V INPUT written on their labels. If you find that this is the case you may want to short D3 terminals to have a driving voltage almost equals to VIN. If you get our kit with the SSR that we supplied you should not have any problem and no actions is usually required.
FAN CTRL  Used to control the oven’s fan if your oven has one.
It is based on the same circuit of HEATERS CTRL so the same considerations about SSR connections are valid. Since this is not switched on and off so often like the heaters you can also use a mechanical relay to drive the fan.
THERMOCOUPLE  You can connect any K-type thermocouple but because we are using a MAX31855 it has to be isolated from GND.
VCC IN  Used to power the board. You should use a power supply with a clean and stable voltage of 5VDC capable of supplying at least 500mA.

 

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What is X-toaster?

X-toaster is a controller board designed to convert any common toaster oven into an SMT reflow oven.
It can drive two external SSR to enable control of the heaters and, if present, the oven fan.
The heart of the system is an Atmel ATXmega128 which can be reprogrammed by the user through the onboard PDI connector. To amplify the signal coming from the thermocouple we selected the MAX31855 which supports any K-type non-grounded probe.
There are three profiles stored in EEprom which can be modified and re-programmed whit your own, to adapt the system to various PCBs, solder pastes and ovens.
Temperature control is provided by a custom PID algorithm with some unique predictive feature to smooth any fast changing ramps in the profile and an exclusive overshoot compensation.
GUI has been designed to work on a 3.2” color touch screen.
Safety features include a programmable timeout, two sensors to check for onboard and external over temperature, oven maximum temperature control, and hardware malfunctioning control.
[box type="warning"]To install and operate this board it is assumed that you have an adequate knowledge of digital and analog electronics, high voltage installations and SMD technology. If you are not an electrical engineer please do not buy this product and do not use it unless you can get some help by a trained technician. Also refer to the DISCLAIMER section.[/box]

 

FEATURES

ATXMEGA128 MCU
MAX31855 K-type thermocouple amplifier
On Board buzzer for alarms and user notifications
Screw connectors for SSRs and thermocouple
Onboard 3.3V regulator (5V regulated input)
3.2” Color TFT display with Touch Screen which allows for standalone operations without a PC
Fast parallel LCD interface for a smooth GUI
Modified PID algorithm to address thermal inertia and hysteresis
On Board LEDs for POWER, STATUS, SSR and FAN
On Board DS18B20 + 3 pins connector for another external sensor
Three pre-programmed profiles for lead and lead-free soldering reprogrammable by the user
For a quick and general use there is no need to open and internally modify the toaster oven
Ready to be mounted on a front panel, supplied with the necessary spacers
Lead Free and RoHS compliant
Industrial temperature range: -20°C ~ +70°C
Board Size: 98mm x 96.5mm

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