Divergence Meter Project


Printed Circuit Boards

I designed the boards using the free software from expressPCB.com, but you probably don't want to just go there and order some because they are quite expensive if you just order single copies. If you are interested in getting some boards, you can contact me. I have ordered additional boards and have some for sale (see the Parts page).

I have posted the artwork and PCB files here in case somebody wants to make their own. As I understand it, the file format that expressPCB uses is proprietary, so I don't know if the files can be easily converted to a format that other PCB fabrication houses can use, but hopefully the artwork here can be a guide for anyone who wants to create files in another format.


Addendum 5-10-2015: Zach, another fan of divergence meters, successfully completed his divergence meter. He re-created my circuit board designs using a program called DipTrace and uploaded them to OSH Park. He wasn't able to take my Express PCB files and open them with that program, so he went through pad by pad and recreated both the IN-14 nixie board and main board. Because his meter is working great, his circuit boards are probably fine (although I have not seen or tested them myself). All together, Zach paid $118 for three of each board (cheaper than ExpressPCB.com). If anyone would like to place an order for boards from the place Zach used, you can use the links he has shared below:

Main Board: https://oshpark.com/shared_projects/OzWVPrP7

IN-14 Board: https://oshpark.com/shared_projects/yB0Dg4q4

There is a difference on Zach's boards: He split the 9v battery input trace where my original board has the option of installing a diode. Zach's board has two pads on the bottom side of the board can be bridged together if you don't want to install the diode, and two through hole pads if you do. Zach reports that his version of the boards have silk screen markings, are ENIG coated, and are very high quality boards.

Addendum 4-25-2015: A fellow divergence meter fan named Thobias paid someone to convert my divergence meter printed circuit board files (which are in ExpressPCB.com's proprietary format) into Gerber format files that he could use to order boards from other companies. He ordered some extra boards to sell, and I pointed recent inquiries about getting boards to him... but he has now sold out of his boards. Because he has sold out, he has granted permission for his files to be posted here.
    This is the link for downloading his files. Note: I do NOT know anything about how he used these files to place an order, so I can't answer any questions about them -- but the files may be useful to some of you for ordering boards from sources other than ExpressPCB.com (if you understand them).


Some discussion of PCB prices:

An example of an inexpensive PCB fabrication house is BatchPCB. They would charge around $39 each for the boards (you need one main board and one tube board, so double that). These boards have silk screening and solder masks. But they take 3 weeks or so to deliver, and the price does not get cheaper for multiple copies. (But the main problem is that my PCB files are not compatible with them...I list them here as an example of a low-cost fab house.)

ExpressPCB (the fab house I used) has several ordering options. If you want the boards with top layer silk screening and top & bottom layer solder masks, the minimum you can order is two copies of the same board for $270.00 ($135.00 each). But if you order 20 copies of the board, it costs $404.00 total (only $20.20 each). More copies work out even cheaper per board, of course. That's nice...but can I find even 20 people who want boards? And remember, this is the cost for just one of the two circuit boards we need to build the divergence meter.

ExpressPCB does allow you to order boards with no silk screening or solder masks for $89.60 for two copies ($44.80 each). Ordering twenty would cost $253.50 ($12.68 each). Certainly cheaper, but you have to do without the silk screen layer and solder masks. I used this service to get my prototype boards made (and paid a bit extra to get four each).

ExpressPCB also has an interesting special deal called their "ProtoPro" service: Four full-up copies of the board, including silk screening and solder masks, for $176.80 ($44.20 each). Not too much more than the inexpensive house, and they are very fast. The board must have an area of less than 21 square inches, but mine do (even the IN-18 versions I laid out). So...if four people ask for boards to build a divergence meter, you are looking at something like $88.40 total for the main board and tube board (plus whatever it costs me to ship them to you).

(The versions of the boards for IN-18 tubes are a bit more expensive because of their larger size...although they would be the same price under the "ProtoPro" deal since that option does not take board area into account.)


My Circuit Boards

The two circuit boards for the IN-14 tube version of the divergence meter are both 6.6 x 1.71 inches in size, and are two-sided boards with plated-through holes. For my prototype boards, I did not pay to get the solder masks and silk screen layer for my prototype boards in order to save money.

As it turned out, my prototype boards worked well and only required the addition of two resistors. In the case of R31, I had extra holes in the board where I needed to add the resistor. In the case of R32, I had to do a little surface mounting of the resistor. My tube circuit board worked fine as it was, and it required no changes.

What I present below are the modified board layouts, which have been tweaked to add the two new resistors. I also added some extra traces and surface mount pads on the back of the board so that (should I ever get one of these new versions made) I can have the option of using a DS3232 high-accuracy clock chip instead of the DS1307 clock chip (but this will require a few software changes). There are also places for components that are not needed in the final Divergence Meter, such as a place for an external crystal oscillator circuit for the PIC chip (in case its 4MHz internal oscillator proved inadequate, but it has been fast enough for me), and an LED that I used for diagnostics while developing the software.

Note that I have indicated are the "top layer" and "bottom layer" of the boards. The "top layers" are where the components get mounted (although the nixie tubes get mounted on the bottom layer). There may be a bit of confusion in that the two boards are actually mounted upside-down inside the divergence meter case, so the "top layers" face downwards.

This divergence meter uses IN-14 nixie tubes because they are readily available and inexpensive compared to other tubes. However, this circuit should work just fine with other tubes -- but that would require laying out a new tube board to match the pin pattern of the other tube, and possibly a new main board to fit to it better.

(In fact, I did lay out boards for IN-18 tubes. There was enough space that the traces from the high-voltage serial driver chips could be snaked around to connect the cathode pins to the drivers in the same order used by the IN-14 board, so the IN-18 board would require no software changes. But for a board for National or Burroughs 5441A tubes, the spacing would be too tight and the lines would have to be run more or less directly as done on the IN-14 board, (which would not match the correct digit pins...but a simple swap table was be added to the software's Loader routine to display the proper digits.

Because my circuit drives the nixie tubes with HV5622 chips, it would not display the "blue dot problem" that can befall IN-18 tubes when certain driver chips are used (I have tested this by having one of my tube boards drive an IN-18 tube that displays blue dots when driven by a KM155ID1 chip -- there were no blue dots). This does not solve the obvious problem that IN-18 tubes do NOT contain a decimal point needed to display world line numbers, but some people would prefer a blank tube there if they could have IN-18 tubes, I guess. If you are interested in tube boards for other nixie tubes, I may be willing to do the layout changes and pay for part of the cost of getting the boards made, assuming they are tubes I'd like to use myself (such as the IN-18 or NL/B-5441A tubes).

My expressPCB format layout files for both boards are in the ZIP file here. This ZIP file includes the circuit schematics and the PCB layout files for the boards.

The artwork for the main board (version 2.0) is shown below (click for full size image). Remember that the outer border of the board is 6.6 x 1.71 inches. This view shows all of the layers superimposed.

main board artwork

Here are the links for the 300 dpi artwork for the

Main board top layer

Main board bottom layer

Main board top silk screen layer


The artwork for the IN-14 tube board is shown below (click for full size image). This view shows all of the layers superimposed.

tube board

Here are the links for the 300 dpi artwork for the

Tube board top layer

Tube board bottom layer

Tube board top silk screen layer



--"Tom Titor" of /a/