Started 14th July 2017

Every line in this is chock full of danger, do not attempt anything described

My grandfather introduced me to soldering, heating the soldering iron in the open flame on the gas cooker in the kitchen, it produced a magical green flame. Moving on to a teenage interest in electronics, I got a Weller iron which lasted me 40 years and still works. It was not creditable that I used the same bit for 40 years. I had a huge tin of flux and when time lagged I would plunge the iron into it for fun.

A more recent revived involvement in electronics saw me give in to "I always wanted one of those" and buy a cheap Chinese made, ebay, Hakko clone, temperature controlled iron (soldering station). The dynamic is different to Weller, one can buy a new iron with bit and carriage from China for £1, but the lifetime of such an iron is often days.

The controller came with an illegal UK plug (no fuse), and inspecting the insides it was worrying to see the earth wire left disconnected. It's cheaper to buy a new iron rather than replacement heaters, even so I've ended up using the Weller to repair it a few times.

What's good about it... well the temperature display gives a clue as to when it is ready to solder, it does reach working temperature faster than the Weller. It's possible to have different irons with different bits.

As a child I positively enjoyed the smell of flux. (Back at primary school, kids would boast how much they liked the smell of car exhaust fumes and breath them in on purpose - that in an age of leaded petrol.) By now flux is a very bad thing, I got a server fan (much more powerful than the average PC case fan) and turned it into a fume extractor. I'm still using 60:40 leaded solder, another very bad thing.

The soldering station is styled 937D - out on ebay the difference to note is between soldering irons (handles) with pins (male) or sockets/holes (female) i.e. on the cable attached to the iron. The female ones have the A1322 element which features a thermocouple for monitoring temperature. The male version has the A1321 element with a thermistor. I am in A1322 land.

Soldering station, David PillingSoldering station, David PillingSoldering station, David PillingSoldering station, David Pilling

First two photos - pins. Last two photos connector on the end of iron cable - holes. The final photo shows the pin connections. The heating element has a resistance around 10 Ω and the thermocouple sensor is about 1 Ω.

There is an eevblog forum discussion: Hakko 936 ceramic heater A1321 vs fake comparison which covers the differences in the two elements, connections etc. From this there is also an A1323 element made of stainless steel, my soldering station came with these, I've never been able to find them at a reasonable price and since they lasted such a short time it's probably not a bad thing.

One way of damaging the element is to try changing the tip whilst the iron is hot.

What I wanted was a way of using one of my irons for melting plastic at temperatures lower than the minimum the controller supports (200 °C). I only intend doing this very rarely. I have a bench power supply that could supply power (DC). Many of the controllers use triacs and are intended for AC.

Searching for "A1322 soldering iron controller" did not produce anything usable, but I eventually found two good designs The Digital Controller for Amazing T12 Soldering Tips and Soldering Iron Controller for Hakko 907. These are for two Hakko variants, the first has a thermocouple in series with the element and the second has a thermistor. A simpler version of the first one would work with A1322 based irons.

Ebay does contain lots of soldering iron control boards, for Hakko/clone variants, but they have the look of closed firmware which makes going with a DIY design attractive.

Soldering station design

My thought was to do something simple. An Arduino Leonardo which has differential ADC along with a built in amplifier, means no analogue electronics. A logic level MOSFET can be driven directly from the Arduino. The user interface consists of a Nokia 5110 LCD display and a rotary encoder. All that spoils this simplicity is needing a buck converter to protect the Arduino from the potential power supply voltage of 24 V.

The soldering iron thermocouple connects directly to the Arduino analogue pins A4 and A5. The MOSFET is driven by digital pin 5 and switches the input power supply to the iron heating element.

Connecting the Nokia 5110 display

//      SCK  (SCLK) - Pin 8  via 10K Ω resistor
//      MOSI  (DIN) - Pin 9  via 10K Ω resistor
//      DC (D/C)  - Pin 10  via 10K Ω resistor
//      RST  - Pin 11  via 10K Ω resistor
//      CS (CE)   - Pin 12 via 1K Ω resistor


  2. Graphic LCD Hookup Guide
  3. Library: LCD5110_Graph
  4. Fast PWM on Arduino Leonardo
  5. IRLB3034PbF datasheet
  6. Modern Thermocouples and a High-Resolution Delta-Sigma ADC Enable High-Precision Temperature Measurement
  7. Using polynomial equation to determine thermocouple temperature
  8. NIST ITS-90 Thermocouple Database
  9. The Ultimate box maker


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Page last modified on August 16, 2017, at 03:14 AM
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