Atten 938D soldering station question

[vehf277]

Hi everybody!

I wanna buy Atten 938D soldering station, http://www.ebay.com/itm/ATTEN-SOLDER...item256f845a64

The soldering iron does not have the sensor, only the heater, 2-core. Is there a way to use it with the other iron having 4-core heating elenment with the sensor by making some mods maybe?

Thank you in advance

[electrosmog]

Re: Atten 938D soldering station question

Thanks for the schematic! I have one of these soldering stations here, and I'm going to try modding it to work with a Weller iron.

Here's how it works: R7 applies a small DC current to the heater. This causes a small voltage to appear across the heater in proportion to its resistance. As it is a PTC ceramic, the resistance depends on temperature. So the heater also functions as the sensor.

This voltage is amplified by IC2 and fed into the CPU's A/D converter. Of course the voltage would be swamped by the 28V heater supply, but the CPU controls the heater, so it simply turns it off before making a temperature reading.

I don't know about other makes, but the Weller irons have a separate 22 ohm platinum resistance sensor. You might well be able to plug this straight in, but you would probably need to change the gain of the amplifier. You may also need a better op-amp than the LM324.

[eccerr0r]

Re: Atten 938D soldering station question

Actually the heater needs to be on to take a measurement (or at least you need to pass current through to measure voltage).

These heater core resistance measuring temperature control indeed do need low noise, low offset op amps to work properly...

Come to speak of it, anyone here make their temp control system for their uncontrollable irons?

[redwire]

Re: Atten 938D soldering station question

I believe the Atten 938 is a clone of the Hakko 938, similar to the predecessor Hakko 936. I would use one of those wands, as the RTD is 43-51 ohms. This forum has more info.

Using heater resistance as temperature (sensor) feedback doesn't work well. There's a big temperature gradient from the heater wire to the tip, so it doesn't reflect on tip temp. Like a pot on the stove, glowing red hot heating element but the pot is much cooler due to lousy heat transfer.