RPM-sensor for the MC-4000

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=82 BGCOLOR="#006699" TEXT="#080000"> <div> <FONT SIZE="5" COLOR="#FFFFFF" FACE="Arial" ><B>JBVM Delemarre</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="JBVM Delemarre"><U><B>home</B></U></A><B> to the Dutch part of my web-site</B></div> <div> <B>RPM-sensor for the MC-4000</B>   |   <A HREF="id79.htm" TARGET="_top" TITLE="RPMsensor electronics"><U>RPM-sensor electronics</U></A>   |   <A HREF="id81.htm" TARGET="_top" TITLE="PCB for the RPM sensor"><U>PCB for the RPM sensor</U></A>   |   <A HREF="id82.htm" TARGET="_top" TITLE="Parts list for the RPM sensor"><U>Parts list for the RPM sensor</U></A>   |   <A HREF="id83.htm" TARGET="_top" TITLE="Photos of the RPM sensor"><U>Photos of the RPM sensor</U></A></div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000"> <div> .</div> <bR> <bR> <div> <A HREF="id49.htm" TARGET="_top" TITLE="This is the English part of my home page"><U>Home to the English part of my web site</U></A></div> <bR> <div> A RPM sensor for the Multiplex MC-4000 and MC-3030 transmitter is presented.</div> <div> It can be build by the average modeler who has some experience in electronics.</div> <div> It needs no difficult adjustments to function properly.</div> <bR> <div> <A HREF="id83.htm" TARGET="_top" TITLE="Photos of the RPM sensor"><U>Photo's of the sensor as made by me</U></A></div> </td> <td valign="top" height=398 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>RPM-sensor for the MC-4000</I></div> <div> Multiplex seems to have ceased the sale of the RPM sensor for the MC-4000 transmitter. Building one from readily available components doesn't seem to be to difficult, but.... </div> <div> Various designs were tested and rejected because the apparent radiofrequent pickup by the circuit was such that the circuit started to oscillate as soon as the supply voltage was derived from the left hand socket at the top of the TX case. Battery power as a supply worked fine but that wasn't to practical. Until recently I tried designs with a photodiode in an operational amplifier circuit that was carefully balanced so even slight variations in the light reflected by the propellor could be used to make a rpm measurement. As said: This didn't function!</div> <div> Recently I started to experiment again after seeing the discussion on the web at the "club-4000" site on the rpm sensor. This time I took another approach and used a phototransistor and placed this device not at one of the very sensitive inputs of the op. amp but used it as a "short circuit" to ground in the feedback loop of an op. amp. applied in a non-inverting setup. Take a look at the circuit scheme and it will be clear.</div> <div> During various experiments with this design build on an experimenters board this worked very fine without any tendency to oscillate even with the supply wires wound around the Tx antenna! So next I designed a PCB and made an unit contained in a small handheld case for field testing. As the results of the initial tests a slight modification was made and an adapted version of the PCB layout was made. This is the circuit with enough information to build one for yourself that is provided in the next pages.</div> <bR> <div> The design is presented so that a modeler with some experience in electronics can build one. <A HREF="id65.htm" TARGET="_top" TITLE="Downloadable files"><U>The PCB layout can be downloaded</U></A> from this site and printed on a desk jet printer or a laser printer using the Easylase program that is also provided. This is a DOS program that will NOT run in the DOS-window of WIndows95-98-2000! After downloading copy the program and the PCB file to a floppy. Shut the Windows system and restart in DOS mode comming from Windows 95-98. When in the windows directory at the prompt type "A:easylase" and press Enter. Then Easylase loads and at the bottom line on the screen fill in the path (!) and exact name of the file you downloaded. In this case it should read something like "A:rpmmpx.pcb" when loading from a floppy in the A-drive. Activate the layer (1) so you see it green in the menu screen, set the output to the printer port (LTP1 in most cases), set the scale factor to 1, and push the "L" on the keyboard and if all is right the layout is printed. I make a very usable transparency for the photo process of etching a PCB using overhead projection printfilm (for desk jet printers) and placing three copies exactly over one and another. I use Scotch tape to keep them in place and use this bundle to print with UV-light on the PCB. The rest in the process of making a PCB is clear I hope.</div> <bR> <div> <A HREF="id79.htm" TARGET="_top" TITLE="RPMsensor electronics"><U><I>next page</I></U></A> will show the electronics involved and a description of the function of various parts.</div> <bR> <bR> </td> </tr></table></body>