I used to have a very nice and compact digital soldering station with a =

5W soldering iron that was very good for just about any general SMT or =

low-power thru-hole work. Unfortunately, I no longer have with me the =

base unit, though I have the actual iron, and I'd like to build a =

PIC-powered base unit.

While the plug that connects to the base has several pins, only two of =

them are connected at the iron side. This particular unit has =

closed-loop temperature regulation, so I figure the temperature sensor =

and iron are connected together in series. I've heated it up using a hot =

air rework station (which claims it was putting out 480=BAC), and measured =

a voltage on the two wires. With the rework station, I managed to get it =

to output 5-6mV. At room temperature, it puts out 0.1mV or 0.0mV. I'm =

guessing it has a thermocouple in series with the heating element.

I've never used thermocouples, so I have no clue how I'd go around =

measuring the output voltage and amplifying it to a suitable value for a =

PIC ADC. I understand thermocouples require a cold junction at the unit =

side and compensation for accuracy, though I don't recall seeing a =

temperature sensor in the base unit (I took it apart a few times). How =

can I tell if the wire from the soldering iron is thermocouple wire or =

plain old copper wire? If it's just copper, my guess is the "cold =

junction" is formed at the base of the soldering iron. I can't really =

take the iron apart without destroying it. I don't need perfect =

temperature readout, since after all I just choose a soldering =

temperature that works well through trial and error. Consistency would =

be nice, however.

FWIW, the iron is a JBC 5W model. Here's a diagram of the entire station:
http://www.jbc.es/pdf/despieces/md3050.pdf
The iron is the "ROD" 5W model.

I'm guessing drive voltage would have to be pulsed (it'll end up being =

pulsed once it reaches the set temperature anyway, due to the closed =

loop), so I would take the temperature measurements between pulses. This =

also means the measuring circuit has to withstand whatever voltage I put =

across the iron (or somehow get disconnected during that time). Also, if =

the time between pulses is short, I'd have to worry about capacitance =

skewing results due to the previous high-voltage pulse.

Ideas?


-- =

Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist