Lab Equipment Projects

To provide a rough overview about the complexity of the projects we will assign
a 1 to 10 open source transistors (the logo of www.openhardware.de):

LAB-Tools made from analog and digital stuff: so we will use nearly everything - in high quality if necessary -

One project may be a frequency counter using a fpga for all the digital counting stuff, a high quality external reference
(e.g. a 10Mhz oscillator in an temperature controlled cabinet), a microcontroller e.g. from the 8051 family to read the registers in the fpga,
doing some user interaction and some controlling tasks. High speed comparators should be used as frontend to get an adjustable triggerlevel.
Also other fine things like prescalers can be imagined...

This is only an idea to give you a feeling about the kind of projects that are here in the future. (This Project would be rated with 8 transistors depending on the degree of sophistication.)

PCB-Photo-Plotter

I one got an old plotter from Roland DG. It has Plotter pens and can be controlled using an old language by roland. Now there are UV-LEDs on the market. So We take Plotter-Pens and remove all the Pen-Stuff from the case. The Pen will be refilled with a UV-LED a Lens to focus the light and a piece of metal with a small hole (diameter=tracewidth) to assign a Trace-Width with the "Pen-Color".
Now we can simply write Traces to the Photo-Resist. We need strong UV-LEDs because the plotter will be quite fast on the paper, so the time for the UV-Light to cause a chemical Reaction in the Photo-Resist-Layer of the PCB is short. This causes the LED to be strong. Unfortunately, UV-Lasers are too expensive (>$200) per piece! So we have to Use UV-LEDs for the Task. The LED in the Holder will be switched on by the Pen-Down-Command. This can be accomplished by adding a Resistor and the Base of a Transistor to the switching-Output for the solenoid which does the pen-down-movement. Our Transistor gets switched by the Solenoid-Signal and can in turn switch on The UV-LED. Beeing more sufisticated, we build a Current-Source which can be switched by the Switch-Signal of the Pen-Down Solenoid.
Properties of Typical Photo-Resist:
Wavelength of UV-Light: 340nm to 320nm
Intensity: 100mJ/cm^3 at 10 seconds

How strong should the light be?
We have an Area of max. 5x5mm (biggest supported trace-width is 5mm.
Hence we gen an area of 25mm^3 which requires 2.5mJ@10 seconds, because 25mm^3 = (100mm^3) * 0.025
Now we assume, that we are at a point for 1/10 Second, so we get a factor of 100 this leads to an energy on 250mJ at 0.1Sec.
Watts is Energy per Time, so we calculate further:
We know: 1J = 1Ws
So why is there a Time given by the manufacturer of the Photo Resist?
They seem to be mad, since the Energy is the Result of Watt and Time. So lets concentrate on the joules and ignore the initial 10 seconds.
We are 0,1 seconds "at the same spot" because the spot also has a width (smaller spots need more intensity) Now we get:
LED-Power in Watts= 0.25J / 0.1 Sec = 2.5 Watts
If we are too strong, we do not harm the process, so we should seek for a strong LED.
For optimum Results use a Laser, but lasers are too expensive.
The Machine is beeing build. Photos will be availlable in short time. Stay Tuned.
Project State: Idea
Last Modification: 07/04/19

Download project PCB-PLOTTER