Soldering station project

[HackoBoy]

hello
First, I apologize that my English is not very good and at times I use google translator
But most of them understand words

I decided to buy a soldering station, but those who themselves control the temperature sensor and heater use - were quite expensive in my city.
After reading information on the internet - I saw that they are working on 24 volts.
I had an old transformer - which I rewound the throttle from a street lamp - and has output parameters:
no load at the output 25.4V  After turning on the car lamp series connect  40 watts + 45 watts = voltage is 23.4 volts - the current in the lamp is 3.8A.
Once convinced that the transformer does not hum and gives a current that I need - I decided to use it. Maybe the voltage is slightly below the required 24 volts, but it will do the job
I liked the  controller Hakko 936 - that no digital thermometer for temperature visualization.
After I saw pdf  - I thought it might add thermometer.

Give advice if possible.
schemes applied to the controller which costs $ 13

http://www.mmccs.com/mmarc/n0ss/hakko_936_schem-pcb_%26_mod_v1r7.pdf

After the thermocouple - signal is amplified by IC2D and IC2A and feed triac driver -> IC1 turning the triac.    Something like a comparator - am I right or not ?
If I take the amplified signal from the thermocouple by foot "pin4  IC1"  if there will be a disruption in the operation of the scheme.

I found two schemes thermometer - but if you can give me a better option.
1:  http://vrtp.ru/index.php?act=categories&CODE=article&article=2137
2: http://www.299792458.ru/news/2010-02-28-14

translate from RUS to ENG
1: https://translate.google.bg/translate?hl=bg&sl=ru&tl=en&u=http%3A%2F%2Fvrtp.ru%2Findex.php%3Fact%3Dcategories%26CODE%3Darticle%26article%3D2137
2:https://translate.google.bg/translate?sl=auto&tl=en&js=y&prev=_t&hl=bg&ie=UTF-8&u=http%3A%2F%2Fwww.299792458.ru%2Fnews%2F2010-02-28-14&edit-text=

But if you can offer me icl7107 scheme to 500 degrees Celsius - I would be grateful

 

[HackoBoy]

hello
I found a circuit filled with ICL7107 and 3 1/2 7seg led  display

After simulation in the program " Proteus 8 professional " - i see the circuit  work well .
After simulation in Multisim scheme soldering station controller
-> It see - out from IC2C - Vref that about 500mV
and the output from  IC2B - voltage varies - from 213mv to 500 mv .
when i build in box - i upload pics .

 

[HackoBoy]

In test this transformer give :
Without load - 24 volts.
50 watts under load -  voltage drop of 23 volts
85 watts under load -  voltage drop of 22 volts

The stand of the soldering iron was not very stable -  - one time is fixed and sometimes not
after  few hour the end result satisfies me 100%.

And later i will add digital thermometer and will fit bottom the key -> information about the current temperature - information coming from the sensor heater

I apologize for the quality of the photos - and if someone does not like manufacturing. But I'm satisfied.