Do you mind sharing your project with us? There are so
many base units which do not fit my requirements.... =


Regards,
John


--- Hector Martin <hector@marcansoft.com> wrote:

> 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
> =




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