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Soldering station simple modification

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KL27x:

--- Quote ---Your reed switch needs to adjust the temp sensor circuit in the handle so the electronics thinks the iron is hotter than it really is.
--- End quote ---
No it doesn't "need" to. Apparently, you did not read my directly preceeding post and/or maybe I am not explaining it very clearly.

It is arguably better to put the reed switch in the stand and make it tweak the actual set temp. For one, if this is one of the irons with a digital readout, you can see it changing so you can figure out when it's working reliably. And you can also see/adjust the actual sleep temp you want. But also because the reading from the heater is probably very sensitive and gets amplified and buffered by opamps before it reaches the control circuitry. Making an adjustment there will be more twidgy. You would also have to stuff circuitry in the handpiece, assuming there is room for this. And how are you going to make the reed switch react to the stand when you are putting the switch somewhere in the back of the handle... you have to make a pretty funny stand.

The pot on the station creates a straightforward, static voltage signal that is the input for a comparator or an ADC with no further signal processing. Tweaking it very precisely is child's play. And you have ample internal space and external real estate to at add additional switches, pots, indicators, circuitry to the station. You also have access to the power supplies. The handpiece has the heater output and a (likely) thermistor in/out that are two nodes in a resistor ladder. And a ground/earth, perhaps. The handpiece won't have the DC rail that feeds the logic circuitry, in most stations.

So not only is there more than one way to skin this cat, the way you have deemed to be the "only" way has no immediately obvious benefit, IMO.

Well, there's one benefit. If you could get the reed switch in the handle to work as you want it to, you would not need to wire your holder/stand to the station. But there are a lot of limitations if doing it this way.

Jwillis:
This is what i would do.Simply desolder the temp control potentiometer bend up to the wiper pin and either on of the outer pins. Solder wires to pins ,solder  wires into PCB holes and one wire to unbent pin of Potentiometer .Soldar wire to pin 2 of DIN plug .Wire up standby pot and relay as shown.
Now you can have the reed switch in the stand or in handle .Makes no difference except attaching a suitable magnet  to handle may be awkward.

KL27x:
This is what I envision as a basic, ELI5 schematic of what I probably failed to describe with words.

You add R3 series resistor on the temperature pot wiper (R2). You insert your additional potentimeter (R1) to adjust the sleep temp to w/e you want.

Of course if you had a dual pole (or is it throw?... I'm throw/pole-dyslexic) reed switch, you could use that instead of adding R3. This would make the sleep temp completely stable despite any subsequent adjustment of the set temp, and would not introduce any noise in the set temp. I don't even know if they make dual pole (throw?) reed switches.

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OP: If you cut power with a relay... your iron goes cold. Or you have to make a new thermostatic control to make it keep a sleep temp. Just use the controls that are already in there, dude.

Jwillis, I have to admit I'm too tired to figure out what you even did there. Kinda complicated.

Jwillis:
There are change over reed switches with 3 pins.Pin 1 is common ,pin 2 is open and pin 3 is closed.But I don't see it being necessary here ,since while the iron is in use ,the relay is simply not active.Provided the relay doesn't draw to much current .the small reed switch he has would probably work provided its normally open. A small 0.5 amp relay would be more than enough.A solid state relay would be even better.
Not sure what voltage this iron runs on ,12v or 24v.
Since the control pot is a voltage divider ,a single resistor approach might not work.
Looking at the diagram I am under the impression the unit is externally powered so any feedback noise would be negligible.But I would try to keep the extra wiring as short as possible inside the enclosure. 

Psi:

--- Quote from: KL27x on April 25, 2019, 05:56:50 pm ---It is arguably better to put the reed switch in the stand and make it tweak the actual set temp

--- End quote ---

That's possible but tricky, If the reed switch is in the stand then you need the magnet in the iron handle.
A magnet will lose it's magnetism if it gets hot so you have to place the magnet away from the hot end of the handle.
That is a problem because the hot end is what touches the stand where the reed switch is.

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