How to make a PCB without using messy and dangerous chemicals
Instead of etching a pcb, run Gerb20.exe
and convert a Newton fleXYcad circuit into Extended Gerber format.
Extended Gerber is an industry standard (EIA RS-274X) and an electronic circuit in this format can be sent to a pcb-maker for the manufacture of a top-quality pcb.
Gerb20.exe (download here) runs on a PC or Linux box and very quickly creates 4 files from one fleXYcad circuit text file.
The design process:
1. Layout the circuit components using fleXYcad on the Newton
2. Save the circuit in the Newton Notes store
3. Transfer the circuit text-file from the Newton to a PC (try using the utility slump.exe)
4. Run gerb20.exe and process the circuit text-file into Extended Gerber format
5. Open the Extended Gerber files in a Gerber Viewer and check the design looks correct
6. Zip up the 4 files with some extra information, and send it to a pcb-maker.
These further instructions supplied in gerb20.ZIP include detailed notes about using Gerber Viewers.
These pictures show details of a new circuit designed on the Newton, then converted into Extended Gerber format by gerb20, and then created by a milling-machine (model: LPKF-Protomat 91S). This latest project (2 small circuit boards) sends heartbeat signals in real-time direct to a PC or Linux box at 19.2k (or 9600) speed, without needing digital storage.
Gerb20.exe has been a complicated utility
to develop and there are limitations in its capability:
1. Gerb20 does not yet create silk-screen information such as component outlines, text, or component ID numbers.
2. Drill holes are limited to 3 sizes: 0.036", 0.048", 0.126" (= 0.9mm, 1.2mm, 3.2 mm). These correspond to small-holes for component legs, medium-holes for switch or trimmer legs, and larger-holes for the D9 serial connector.
3. Design rules are relaxed in order to get gerb20 working e.g. the amount of copper around a drill hole is user-selectable by changing the pad-size, and it may be less-than-optimum around the medium-size holes.
Drill sizes provided by different pcb-makers may
vary e.g. some will be Metric, some Imperial, and their sizes might not
exactly match the 3 Imperial drill sizes required for gerb20. Some
drills may be smaller, some larger.
Determine the drill sizes offered by a pcb-maker beforehand - such information should be on their www pages and it might be called a drill-rack.
If the pcb-maker cannot exactly match the drill sizes required for gerb20, and they offer a slightly larger equivalent drill size, then there may be less copper around the drill hole on the finished pcb. In this event, try using a larger pad-size in gerb20 before sending the board to the pcb-maker. Be sure to use a Gerber Viewer to check the tracks and pads.
Alternatively, it is also very easy to change
a gerb20 drill size in the output drill file.
In the drd.txt file, just edit the appropriate Imperial drill size in this list:
e.g. depending on the pcb-maker, 0.044 or 0.046 might be a better choice than 0.048".
Be sure to review any changes to the file by using a Gerber Viewer.
Ideally, these drill sizes need to be in a preferred dimension e.g. some drill size ranges will only jump in 4 mil steps (4 mil = 0.004").
Some milling-machine software may generate an
error with this drill format and require instead:
where the space has been replaced with C0.
The first two trial boards for the new Heartbeat
project used drill-holes of 0.040" and 0.052", with a pad-size of 8x6.
There was insufficient copper around some holes, and with hindsight, a better choice of pad-size would have been 8x7 or 9x7. The latest boards have smaller drill holes of 0.036" and 0.048", with a track size of 0.025" and a pad-size of 9x7, and this combination provides a better area for soldering.
To run gerb20.exe on a Linux PC, install
(a DOS emulation utility).
To use a Gerber Viewer on a Linux PC install wine (a Windows emulation utility). ViewPlot will run, but not ViewMate.
gerb20.exe has been tested on half-a-dozen circuits and appears to work, but there may still be some bugs in the code.
Three pairs of milled-boards have been made in a first trial, followed by 5 boards in a second test.
The term 'pcb' on these www pages means both printed or milled boards.
Comprehensive list of pcb information and www sites here.
Useful account of PCB design rules here.
The milled circuit-boards for this project were supplied in the UK by: tswelectronics_at_googlemail.com, to whom enquiries may be made for the production of other single or double-sided boards.
Updated: 17 November 2008.