Revision as of 16:01, 2 July 2015

SMD SolderStation for Weller RT series

  Six Wiki pages and to files are related to this manual: 
 
 *  Les instructions de chargement du firmware (version Française) 
 *  Une presentation générale de l'appareil (version Française)
 *  Le guide de montage illustré (version Française)    
 * File:BOM Station CMS.xls The Bill of Material, xls format
 * File:BOM Montage.xls The Assembly BoM, xls format
 
 *  Loading the firmware, (English version)
 *  Assembly Manual, (English version)
 *  A quick general presentation of the solder station(English version) 

How is working this stuff

This project is based on Martin Kumm DC3MKB’s project (http://www.martin-kumm.de/wiki/doku.php?id=Projects:SMD_Solderstation), published in July 2014. Martin made a very interesting hack : using an Arduino Uno and a Weller soldering iron tip to build a low cost professional soldering station.

Other soldering stations based on the same recipe came to life almost everywhere. Including the one made by Andreas, DL4JAL (http://www.dl4jal.eu/smd_loetstation/smd_loetst.html), who preferred to use a Microchip PIC18F2520 microcontroller. The power front-end and the temperature input network are strictly the same as these made by Martin. Its main disadvantage is that a newbie will have more difficulties using PIC MCUs and will have a harder time to change the firmware, compared with the DC3MBK approach. An Arduino is directly programmable using a simple USB cable.

The working principle is simple: The tip of the iron include both the "soldering tip" itself, the heating resistor and a temperature sensor.

The Arduino, for its part, uses this probe to read (A7 port) the iron temperature, and compares this value with the preset temp. requested by the user. If the measured temperature is too low, the Arduino increases the duty cycle of a PWM (pulse width modulation) output on the D3 port. Otherwise, if the temperature is too high, the duty cycle decreases. This strobe of variable width pulses is used to “more or less” briefly open and close the power supply circuit of the iron, or more precisely the integrated heating element located into the tip of the iron. This closed loop -measuring, comparing a setpoing, proportionally changing the value of a current flowing in the circuit- is a “classic” of the “process control” world, and is called a " PID loop " (proportional-integrated-derived).

Why a temperature control system

Electronic geeks, Ham Radio or hackers, do not longer use discrete “thru hole” components, but more and more surface mounting devices. These devices require very precise soldering temperature ( eutectic), which may vary very strongly depending on the type of wire that is used, the class of compounds which is employed and the nature of the solder contact.

- The solder wire is a polymetallic compound whose melting point depends on the nature of the metals that compose it. A tin-lead-silver alloy melts at 178 ° C, a tin-lead at 183 ° C, tin-copper-silver (said "ROHS welding") to + 217 C, and a tin-copper at 227 ° C . Without precise control, it is difficult to precisely reach this point. Too cold, the tip cannot melt the solder wire, too hot, it will accelerate the oxidation of the alloy and cause microcracks. Worse, with the new lead-free solders, poor temperature control will cause micro-whiskers that could eventually cause short circuits.

- All components are not created equal in terms of temperature resistance and thermal shock. Resistors are ... more resistant to long contact with a hot iron tip. That’s definitely not the case with quartz or some active components.

- The nature of the solder pad can cause troubles. On a PCB with a large ground plane, heat dissipation is such that it can "cool" immediately an iron tip if this one is too thin and offers little thermal inertia. The copper of the PCB is an excellent heat radiator. To minimize this problem, it is advisable to use "thermal breaks" on each grounding pad or connected to a large copper plane ... and / or to increase the heating temperature of the tip itself(thus meaning a very good and efficient temperature control).

Why this kind of soldering tip

- Because it has been manufactured by of one of the most serious manufacturers of soldering tools. Some members at Electrolab have Weller stations for over 35 years and still find spare parts needed to maintain them.

- Because it has nearly fifteen different soldering tops with different forms and shape ranging from the microtip for delicate SMT components (0402, QFN, TSSOP) to "chisel" and "screwdriver" tip of 2,2mm

- Because it heats in less than 5 seconds and 10 s to cool down, allowing an almost instantaneous changing of a tip with another one ... with other older soldering stations, this kind of operation was requiring at least two different soldering iron.

- Because such quick heating and cool-down time coud also be triggered by a “sleep” or “stand by” control system which saves energy and prolongs the life of the soldering tip.

- Because the price is affordable, between 28 and 35 euros (without VAT)… almost the price of an entry-level soldering station made in China.

-

'The different parts

• An Weller iron soldering tip RT series.
• An Arduino Nano
• Some peripheral devices, including an operational amplifier for temperature measurement (amplification of reading the sensor data), a power FET charged with supplying the current to the heating resistor of the iron
• A man-machine interface, pompous term for either a triplet of 7-segments displays and a rotary encoder (or an optional color LCD screen), and a yellow LED used to indicate that the preset iron is heating.
• Two printed circuit boards, one supporting the Arduino –the MCU board-, the other the interface –the Display board.

'Accessories and options'

• A box depending of your junkbox, taste etc…
• A 12 V DC. The less adventurous hackers will opt for a "Switching" molded 220V / 12V power adapter, "warrior" will manufacture their own powersupply with a 220 / 9VAC transformer, a diode bridge and a big filtering capacitor of 8-12000 uF
• An AC filter (Schaffner for example)
• Some connectors linking the Weller tip to the cable, and the cable to the housing
• An soldering iron rest (with or without standby circuitry)
• A bronze wool sponge
• Three Molex "KK" in no 2.54mm (this is frankly an overkill and unnecessary option)

The Electrolab Kit

The Electrolab Soldering Station kit available in 3 versions

A warrior version that includes, for only 5 Euros

• The two basic circuit ... and the BoM (list of components).

A full kit which includes, for only 35 Euros

• The 2 PCB ("7-segment displays" and MCU)
• All active and passive components
• A stereo jack compatible with RT soldering tips
• An "Aviation" connector (output of the solderstation’s housing)

A more than complete kit for only xxx Euros which includes

• The “full kit” edition
• An original Arduino Nano
• A Weller RT soldering tip

This soldering station needs a 12Vcc/60W input voltage(not include). Any kind of 12V switching power supply easily found on eB will do the job.

Note also that Ham radio and other “low signal/high frequency pundits”, who often use components such as AsGa transistors and highly sensitive and fragile component which could not cope with static and transient voltage coming from the 220V main, prefer to use series-regulated power supply with a good old transformer, a diode bridge, filtering capacitors etc.