Recently – while browsing eBay – I came across a Weller DSX80 desoldering iron. Below I will describe extensively how to use the DSX-80 without buying the expensive soldering station that you are supposed to use it with.
This German beauty uses a heated tip with a hole in it through which a vacuum is pulled by pushing a button. This allows you to desolder through hole components effortless. It can be found on eBay for around 80 euros.
Frustratingly the accompanying soldering station (The Weller WDD-81V) cannot be found cheaply online. This station uses a compressed-air inlet, a Venturi effect vacuum generator and a solenoid valve (controlled with the button on the iron) to switch the vacuum. It outputs it’s vacuum through a little connector below the 7 pin connector.
However, the Weller WSD-81 is very abundant on eBay and relatively cheap (about 60 euros). It uses the same 7 pin proprietary Weller connector, thus it can deliver enough power for the DSX-80. If you connect the switch on the iron to a solenoid valve connected in between an external vacuum source, you have a fully working DSX-80, for a fraction of the retail price. Easy, right? That’s what I thought when I had this idea in my mind. It turned out to be quite challenging. Read on below to see what things I decided to use to emulate the WDD-81V, and how I connected everything.
In order to make this work with the WSD-81 we need to figure out these things:
- What vacuum source
- How to switch the vacuum on and off
- How to use the button on the iron
- How to integrate all this
The vacuum source
Because air compressors can be a bit expensive, large and noisy, I decided to use a vacuum pump. I thought about salvaging the compressor from an old refrigerator, but then I came across the Aoyue 933. It is marketed as a solder fume absorber, but it works just fine as a cheap vacuum pump. It’s cheap price (35 euros) made me choose it over fooling around with a refrigerator compressor. It provides about 0.8 bars of vacuum, which is the same as what the WDD-81V provides.
But you are free to use any way of generating a vacuum you want (venturi vacuum generator (commonly called ‘ejector’)/ old pumps/…).
A way to switch the vacuum on and off
I used a 12V DC normally closed solenoid valve with 1/4 inch to barbed adapter to connect to hoses. Find one like this on eBay:
A way to use the button on the iron
Below is a picture of how the button is connected in the handle of the DSX-80. I couldn’t find any schematic of the controller board.
As you can see, pin number 7 is either connected to ground or pulled down through a 44k ohm resistor. There is no way to use this switch directly.
I soldered 2 wires to the pins on the controller board to see what the button does.
Putting any voltage on pin 7 will offset the ground of the controller board inside the WSD-81, which results in incorrect temperature readings. I measured the voltage at pin 7, with pin 1 as ground. It’s about 5V when not pressed, and 0V when pressed, drawing any current from pin 7 will collapse the voltage. I tried to directly switch a P-channel MOSFET with that voltage but it didn’t work, it drew too much current, which caused the gate source voltage to be too low.
So I needed something that inverts the signal which is presented on pin 7 (because the relay is normally closed), and has a high input impedance, a CMOS inverter IC! I came up with this circuit, using an old school CD4049UBE.
VIN is sourced from the large input capacitor of the onboard 5v regulator of the WSD-81.
After some testing on the breadboard I made the final circuit on some perfboard, and added some screw connectors:
The incoming wires are (from bottom to top) the switch signal (pin 7), ground (pin 1) and +16V unregulated (from the onboard regulator). On the left the solenoid valve connection.
I choose to put the solenoid valve and my perfboard circuit inside the vacuum pump. This way I can easily tap into the internal tubing to connect the valve in between. In order to connect the WSD-81 to the vacuum pump, I used some 5 pin DIN connectors I had laying around from an old project to make a sturdy connection. I drilled a hole in the bottom of the pump to mount the solenoid valve, and I hot glued the perfboard to the back of the front panel of the pump.
Below are some pictures of this: