Page updated August 2022
This page contains a number of files that accompany the article "REVMASTER - A Simple Tachometer", published in Model Engineers' Workshop issues 115 and 116.
These files are copyright 2006, Tony Jeffree. They may be downloaded and used FOR PERSONAL, NON-COMMERCIAL PUROPSES ONLY.
The PDFs contain updated copper track and silk screen layouts for the single line display (issue 115 figures 2 and 3) and the 2-line display (issue 115 figures 4 and 5) versions of the board. There are two versions of each pair of diagrams; the ones labelled as "0-22 pitch" have the slotted sensor board laid out for the slotted sensor mentioned in the article - RS part 303-1192 (OPB365T55), which has a 0.22" gap between the LED leads and the phototransistor leads. The ones labelled "0-32 pitch" have a 0.32" gap between these pairs of leads, and would suit RS part number 455-8020 (OPB360T51) which is identical in all other respects.
An alternative part, RS 301-8442 (OPB620) also has a 0.32" pitch and could be used; its response times are slower than the original part, but it is cheaper and doesn't have any mounting lugs that would otherwise need to be chopped off. It is a slower part than the others, but for most purposes should work fine. I haven't checked whether the resistor values would need modifying to work with this part, so it would be worth checking the specs to ensure the correct current flow through the sensor and adjust their values accordingly if necessary.
NOTE that, unconventionally, the copper layouts are presented as viewed from the component side of the board; this is ideal for use with the "laser printer transfer" resist method described in the second part of the article (MEW issue 116); you may need to reverse (mirror) the copper layout to use it with conventional photoresist techniques. If you want to use the silk screen with the laser printer transfer method to print the legend on the boards, you will need to mirror them first.
Rev counter 1 line 0-22 pitch copper 06-05-23.pdf is the copper layout for the single line, 0.22" pitch board.
Rev counter 1 line 0-22 pitch silk 06-05-23.pdf is the silk screen layout for the single line, 0.22" pitch board.
Rev counter 1 line 0-32 pitch copper 06-05-23.pdf is the copper layout for the single line, 0.32" pitch board.
Rev counter 1 line 0-32 pitch silk 06-05-23.pdf is the silk screen layout for the single line, 0.32" pitch board.
Rev counter 2 line 0-22 pitch copper 06-05-23.pdf is the copper layout for the two line, 0.22" pitch board.
Rev counter 2 line 0-22 pitch silk 06-05-23.pdf is the silk screen layout for the two line, 0.22" pitch board.
Rev counter 2 line 0-32 pitch copper 06-05-23.pdf is the copper layout for the two line, 0.32" pitch board.
Rev counter 2 line 0-32 pitch silk 06-05-23.pdf is the silk screen layout for the two line, 0.32" pitch board.
The following Zip file contains the "C" code and header file used to generate the firmware for the project, plus the HEX file that needs to be programmed into the PIC 16F84 chip. Fuse settings should be chosen for HS clock, no power up timer, no watchdog.
PLEASE NOTE that these files were developed for use with the FED PIC "C" development tools; they call for the use of library files that are part of the FED "C" development environment. You may need to provide equivalent library routines to handle the displays if you use a different development environment.
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website ({at}) jeffree.co.uk
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