Homebrew PCBs

Hello Stefan, Steve,

The way compressed air is used to dispense a paste, is to use a two-
way valve or two valves. First the valve is on comperssed air for a 
specific time and pressure, providing the decided amount of paste.
Then the valve is switched to open air, so the pressure is released 
instantly, so no drips anymore.

Important in this is that there is no air or gas pocket in the 
syringe. The syringe will be normally airless for this reason if you 
buy it.

A leadscrew will of course also work, but will make the system very 
long and less practical to use.

Another option is a gearpump, dispensing the paste and then 
eventually suck back to compensate for trapped air. But this is much 
more complex.

Gertjan.


--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan 
<stefan_trethan@g...> wrote:
> 
> >
> > Did you build the temperature control part, then?
> 
> Yes i did build it, no i don't have the schematic anymore.
> Back engineering would work, it is not too hard.
> it used a triac to switch the current, and there is a opamp
> / comparator somewhere. ther is also a led for voltage reference.
> it has a display for temperature, which is so wildly inaccurate that
> i do not use it (could calibrate it).
> it can be built without the display too.
> it is a simple control circuit, i could build it from scratch i 
think.
> you have a potentiometer for setting the temperature you like. and 
a led
> that blinks with the heating element. i added a piezo speaker 
which "ticks"
> on each heating, sounds like a geiger counter but it doesn't let me 
forget
> to switch it off (left it 2 times overnight before adding the 
ticker).
> it is also a nice audible feedback if it is hot...
> 
> 
> It was made some time ago in school. sorry i didn't keep the 
schematic.
> (stupid i know...)
> 
> If one really needs to build one i draw it up from the pcb, it is 
not
> too complicated.
> However you need a 24V iron for it, which alone did cost 600ATS 
when i 
> built the
> unit. (50 eur or so) now you can get complete stations for less (ok 
they 
> are bad..)
> 
> 
> > I really like the idea of a slide-through oven with a pre-heat 
chamber.
> >
> 
> Me too. i think it is the only sensible approach.
> even if you have a 3MW heating element ( ;-) ) then you would
> still need to heat the air, the heating would take longer.
> with a hot oven it is the fastest possible with air.
> 
> 
> 
> > Yes, I'd think compressability of air would rule it out.
> >
> > How about a leadscrew and stepper motor?
> 
> maybe a useable idea.
> the paste comes filled in a syringe already...
> 
> I wonder if it would work on a cnc to automatically dispense the
> paste, if one can ensure that the dot comes out and sticks to the
> pad, not the needle. with some tweaking it might work....
> 
> 
> then add a pick and place ;-)
> 
> ST