Need some tips for a DIY solder station.

[rwgast_lowlevellogicdesin]

So recently my 40 watt weller broke down, and I went to RS and bought a 15/30W Iron. The RS Iron is HORRIBLE, at 30ws it burns up tips and at 15w it does not retain enough reserve heat to be useful, and I use small .032 60/40 solder. I really liked my 40 watt weller but I would like something a bit better and I don't have a whole lot of money. What I do have is enough for an Iron and all the parts I need to make my own station. I feel like I have two options:

The first would be to purchase another solid 40 watt weller, or Hakko 508. Basically any decent quality standard iron will do. Then I could just ass a light dimmer to it like most everyone else to get heat control. If I went this route there are two things I'm a bit hazy on. First off I do not want to buy an a dimmer at the hardware store with a big ugly knob! I looked around on digi key at pots and couldn't find any that seemed suitable. If I have a 40 watt iron I would need at the least a 40 watt pott, probably a bit bigger correct? Secondly if I wanted to use a micro to read the pots position to display a percentage would I use an opto-coupler for that?

My second option is to build a fully digital station with a current feed back loop, that way I can solder at 15w and not have to worry about heat loss, this is the better option in my opinion. It does not seem all that hard actually! Maxim maks a great chip the MAX31855, http://www.maximintegrated.com/datasheet/index.mvp/id/7273 it basically takes care of all the tempature readings for you so all you have to do is raise the power.  The two questions I have on this method is how exactly would you digitally control the current on the mains. Secondly Would any iron with a 5 pin plug for a solder station be about the same as far as the sensors inside? I have found these irons with the thermo couples built in for as low as 12 bucks, Im fine with a cheap   one as long as I can throw a nice hakko or weller tip in it. Since I am building the station my self I can buy a much nicer "pencil" when I have money as long as it feeds the same data to my station as the cheap one.  I found this hakko 907 compatible iro for 8 bucks http://compare.ebay.com/like/390562392942?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

[Psi]

You're going to spend more than $16 buying parts to make something.

So the cheapest option is to buy one of those $16 soldering stations and get some good quality hakko clone 900M tips for it.
(The official hakko ones don't quite fit apparently, unless you file the hole a little bigger)

http://www.hobbyking.com/hobbyking/store/__19240__Soldering_Station_with_Adjustable_Heat_Range_USA_Warehouse_.html

I would open it up and check the mains wiring before turning it on though.

Worst case, (if its crap) you can use the case and other parts as a base to build your DIY station.

[rwgast_lowlevellogicdesin]

Ok here is the thing, I would really like a digital set up with feed back. Like I said before I have almost all the parts I would need, lcd's micros. passives, enclosure, Hi side current amplifiers, precision shunt resistors, and I can sample the maxim chip for free! All I would really need to buy is the iron and a few components. But since you posted that I may as well ask, if I were to go with a simple open loop type set up... I really have two choices I can buy something like you linked too, I have seen a lot of decent 40w elenco stations that have the stand and sponge for 20 to 30. Is there any way something like that would be a better choice than a quality Hakko with a pot on it?

As far as a digital set up goes, I posted this before

http://www.ebay.com/itm/24V-50W-5-PIN-Soldering-Station-Iron-Handle-Compatible-HAKKO-907-926-928-936-937-/170996602602?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D390562392942%26ps%3D54

it is an 8 50w dollar hakko 907 compatible iron, with the 5 pin plug, meaning it has the opto couplers in it, and should take hakko tips. What I just noticed is it says 24v DC, this may make my life even easier, I would not have to do any isolation of the AC mains correct? All I would have to basically do to get the iron working is build/find a 2amp 24v power supply/wal wart, and then I could connect that to the +/- pins of the Iron and have the thing working at the full 50watts. After that I would use the maxim chip to read the sensors. Next I would drive the use either a half h-bridge or some fets to amplify a PWM signal from a micro  to the iron. Does this sound correct?

[rwgast_lowlevellogicdesin]

Darn it says 24vc AC acually so I guess the above method is not the correct way to go about this.

[Psi]

Most of the soldering stations i've seen (which isn't many) use a typical mains transformer to supply ~24VAC.
The temp sensor is used for feedback and the difference between it and the temp knob position drives a triac to chop the 24V waveform and maintain the set temperature

The cheap ones may not have a temp sensor though.

[peter.mitchell]

I've wondered how cheap it would be to make a DC SMPS with adjustable current limit compared to make the traditional AC one, one transformer can buy you a lot of chips.

[Psi]

one transformer can buy you a lot of chips.

That's quite true if you're looking at transformer prices on digikey/element14/rs.

If you're a factory in china though, then no. Transformers are a few seconds of labour and labour is cheap!

[peter.mitchell]

one transformer can buy you a lot of chips.

That's quite true if you're looking at transformer prices on digikey/element14/rs.

If you're a factory in china though, then no. Transformers are a few seconds of labour and labour is cheap!

The same could be said even more so for cheap chinese chips.
Also, that wasn't looking at digi/farnell/rs/ele14 it was alibaba/taobao.

[rwgast_lowlevellogicdesin]

Hey thanks a lot for the tip on that Hobby King station the more I look at it the more I think It is the best choice. It has a Hakko clone Iron with the 5 pin connector, so im guessing there is it has a temperature sensor in it, and it also has the whole circuit to run the heater. I am not really familiar with triacs, an you are right with a 24v transformer built in to it you cant beat $16. So the best idea would be to buy this station and modify it to to read the sensors and provide feedback.

[smashedProton]

Just get a fx-888...  they are only like 7 hours of work