{"id":141,"date":"2007-08-07T20:08:44","date_gmt":"2007-08-08T01:08:44","guid":{"rendered":"http:\/\/freemansgarage.com\/blog\/?p=141"},"modified":"2020-11-07T08:31:41","modified_gmt":"2020-11-07T13:31:41","slug":"homemade-optical-tachometer","status":"publish","type":"post","link":"https:\/\/www.freemansgarage.com\/index.php\/2007\/08\/07\/homemade-optical-tachometer\/","title":{"rendered":"Homemade Optical Tachometer"},"content":{"rendered":"<h3>The Tachometer<\/h3>\n<p>The tach will measure RPM of an R\/C helicopter rotor using a shutter effect by rotating a disc at a known RPM and displaying the result on a LCD screen.\u00a0 \u00a0The user looks through a \u201cview hole\u201d and attempts to stop the blades with the shutter speed control.\u00a0 When the disc RPM matches the rotor RPM, the rotor will look like its not rotating.\u00a0 It\u2019s a very simple concept and works very well for this application.\u00a0 The memory button when pressed will take a \u201csnap shot\u201d of the RPM at that moment and display it on the screen.<\/p>\n<p style=\"text-align: left;\">This project requires some fairly good soldering skills and some fabrication ability is helpful.\u00a0\u00a0 I have a full workshop with a mill, lathe, drill press, and other tools which greatly helped.\u00a0 If you do not have access to a workshop, you will have to make due with a hand drill and a dremel or whatever you happen to have.\u00a0 I will try to keep this simple but yet give enough info so you can understand what is going on. \u00a0\u00a0I advise that you read the entire document before starting.You can get some tips and ideas from several others that also built this tach. I posted this project at <a href=\"http:\/\/www.helifreak.com\/\">www.helifreak.com<\/a> in the tech room.<\/p>\n<p style=\"text-align: left;\">Here is a direct link: <a title=\"Finless  Bob's Helifreak Tech Room\" href=\"http:\/\/www.helifreak.com\/showthread.php?t=73354\">Finless Bob&#8217;s Helifreak Tech Room<\/a> for added support. Also feel free to email me if you have any troubles.<\/p>\n<blockquote>\n<p style=\"text-align: left;\">Tools Needed:<\/p>\n<ul style=\"text-align: left;\">\n<li>20 Watt Soldering Iron \/ Pin<\/li>\n<li>Wire Cutters<\/li>\n<li>Rosin Core Solder (smallest diameter you can find)<\/li>\n<li>Small hobby saw<\/li>\n<li>Screw Drivers (Phillips &amp; Straight)<\/li>\n<li>Drill<\/li>\n<li>Dremel \u00a0(or your neighbors workshop)<\/li>\n<li>Multi-Meter<\/li>\n<li>CA or Epoxy<\/li>\n<li>PIC Chip Programmer (more on this later)<\/li>\n<li>Black electric tape<\/li>\n<\/ul>\n<\/blockquote>\n<p>18 pin chip socket\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Socket for PIC 16F628A\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Optional and not req\u2019d.<br \/>\nAll of these parts can be purchased at <a href=\"http:\/\/www.futurlec.com\/\">www.futurlec.com<\/a> ,<a href=\"http:\/\/www.mouser.com\/\">www.mouser.com<\/a>, or <a href=\"http:\/\/www.digikey.com\/\">www.digikey.com<\/a>.\u00a0 I personally like Futurlec because they have the hobbyist in mind and their site is very easy to find items but their shipping is slow. You can buy them from anywhere you feel comfortable. You are welcome to substitute items such as the IR sensors and LED\u2019s for other brands or types.\u00a0 Anything will work as long as it can see the rotating disc.\u00a0 A hall effect sensor could easily be used just like the heli hall effect sensors on the governor.\u00a0\u00a0 Buttons and switches are not critical and anything will work.\u00a0\u00a0 The critical items:\u00a0 PIC16F628A, LM7805, 317T, the HD44780 LCD screen, and the resistor values.\u00a0\u00a0 My schematics are based on those items and if you swap them out you may have to alter other parts and the software code.<\/p>\n<p style=\"text-align: left;\">Parts List: Description Comment<br \/>\nLM7805 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 5v voltage regulator\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 T0-220 size<br \/>\n10uF cap \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Electrolytic capacitor\u00a0\u00a0\u00a0\u00a0\u00a0 Any voltage rating will work<br \/>\nQSE114 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Phototransistor (IR)<br \/>\n4.7K ohm (two)\u00a0\u00a0\u00a0\u00a0 1\/8 watt resistor<br \/>\n1.7V IR LED\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Infrared LED<br \/>\n317T \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Variable voltage regulator<br \/>\n10K Trimpot\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 10K ohm potentiometer<br \/>\n1N4002\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Diode<br \/>\n2.5K pot\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2.5K ohm Precision Pot.<br \/>\n16&#215;2 LCD \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 HD44780 Controller type<br \/>\nPIC 16F628A\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 18 pin Pic Micro Chip<br \/>\nSwitch\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Power switch\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 can be any type of switch<br \/>\nPush Button\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Micro Push Button\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 can use any type<br \/>\nKnob\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Knob for 2.5K Pot.<br \/>\nWire\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Misc. small wire<br \/>\nProject Box\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 102 x 68 x 37 mm<br \/>\nExperimenters Board\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 120 x 80 mm.<br \/>\n150 ohm \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 1\/8 watt resistor<br \/>\nMotor\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Small dc motor\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 kids toy?\u00a0 servo?<br \/>\n9v Battery\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Battery<br \/>\nScrap Balsa or plastic<\/p>\n<h3><span style=\"text-decoration: underline;\"><a name=\"ASSEMBLY\"><\/a>Assembly:<\/span><\/h3>\n<p><span style=\"text-decoration: underline;\">Step 1<\/span><br \/>\nYou need to make the rotating shutter disc.\u00a0 Mine is about 2\u201d in diameter and has three equally spaced slots cut into it. \u00a0The diameter can be changed to suit your box size but it must have 3 slots as shown and keep the slot width 0.250\u201d or less. \u00a0It needs to be thick enough to withstand 300-1000 RPM. Mine is 0.050\u201d thick or so and is made out of carbon fiber.\u00a0 You can make the disc out of anything such as balsa, plastic, thin plywood, or metal.\u00a0 My first disc was balsa and worked quite well.\u00a0 The center hole needs to fit tightly on the servo motor shaft in which you will glue it with epoxy or CA.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1365 alignnone\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/tach_clip_image0021.jpg\" alt=\"\" width=\"420\" height=\"315\" \/><\/p>\n<p><span style=\"text-decoration: underline;\">Step 2<\/span><br \/>\nThe project box needs a few cut-outs and holes.\u00a0 The location of the holes is not critical and should suit your needs.\u00a0 I was able to fit everything in my plastic box with the holes located in the diagram below.\u00a0 You need to place the motor and shutter disc assembly from Step 1 into the box to get a rough idea where the view hole needs to go.\u00a0 The same applies for the LCD screen, memory button, and the 2.5k pot.\u00a0\u00a0 They all need to fit in the box without rubbing the shutter disc.\u00a0 This was tricky but can be done.\u00a0 The slots on the shutter disc must pass in front of the view hole for this to work.\u00a0 You should be able to see through the disc when it\u2019s spinning. The LCD screen should fit into the opening with no resistance.\u00a0 Do not force the screen because it\u2019s extremely fragile.\u00a0 I broke one already trying to force it into a smaller hole.\u00a0 There are two more small holes not shown and they are for the 10k trim pot and the power switch. These can go anywhere you choose and mine are on the bottom side.<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"alignleft size-full wp-image-1366\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/box1.jpg\" alt=\"\" width=\"600\" height=\"450\" \/><br \/>\nI glued the motor to a piece scrap balsa to hold it in its final spot.\u00a0 Do not glue anything until you are certain of its location.\u00a0 As a reference you can see how I fit everything in there from the picture below.\u00a0 It\u2019s a tight fit and might take some adjusting but you can get it all in there with room to spare.\u00a0 The image below is the project box with the back cover removed so you can see where everything fits.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1367\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/everything20fits1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><\/p>\n<p style=\"text-align: left;\">You can not see them but the IR LED and the QSE114 sensor are under the balsa spar.\u00a0 The computer (PIC 16F628A) has to be able to \u201csee\u201d the spinning shutter disc.\u00a0 To accomplish this we use an Infrared beam of light.\u00a0 The IR LED will not be visible to the human eye so it\u2019s hard to tell if it\u2019s working.\u00a0 I used a multi-meter set on milli-amps and measured a few milli-amps in the circuit to see if it was working.\u00a0 If it\u2019s off you will get zero.\u00a0\u00a0 The IR LED needs to shine through the disc slots and the QSE114 sensor needs to be mounted on the opposite side of the disc to \u201csee\u201d the Infrared beam (see diagram below).\u00a0 This works exactly like those garage door opener sensors that are mounted by the floor on your garage door.\u00a0 If you get in the way of the garage door sensor beam, the door stops going down.\u00a0 In our case with the tach, the slots in the spinning disc will repeatedly break the infrared beam allowing the computer to \u201cread\u201d the pulses from the sensor.\u00a0 The computer simply counts the pulses for a given time span and knows exactly the RPM of the disc.<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"alignleft size-full wp-image-1368\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/sensor20setup1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><br \/>\nIR LED and Sensor setup for the shutter disc<\/p>\n<p><span style=\"text-decoration: underline;\">Step 3<\/span><br \/>\nThe electrical side of this project is the more difficult part.\u00a0 I drew up some schematics and tried to simplify it the best I could.\u00a0\u00a0 Take your time and check your work and you will be fine.\u00a0 I recommend building this in some sort of breadboard and get it working first.\u00a0 Afterwards, go ahead and solder everything in place.\u00a0 This is of course optional and not required, but it saved me some headaches.<br \/>\nThe easiest way to build this is to break up the circuit into 4 smaller circuits.\u00a0 These 4 circuits connect together to make the final bigger circuit.\u00a0\u00a0 It is much easier to work on one part at a time and get it working 100% before moving on to the next one.<br \/>\nThe Motor Circuit:\u00a0\u00a0\u00a0\u00a0\u00a0 This is the motor circuit.\u00a0\u00a0 The 2.5K pot will be your fine tune adjustment knob for the shutter speed.\u00a0\u00a0 The 10k trim pot will set your max RPM level.\u00a0 Once it\u2019s set to your liking, the 2.5K Pot will fine tune the RPM from 900RPM to the MAX level you set.\u00a0\u00a0 There is no need to solder this on a circuit board.\u00a0 I just glued the 317T to the side of the box.\u00a0\u00a0 The battery connects to the input.\u00a0 Note: You will only use two of the pins on the pots (they have three pins).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1369 alignnone\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/tach_clip_image0011.gif\" alt=\"\" width=\"471\" height=\"422\" \/><\/p>\n<p><span style=\"text-decoration: underline;\">The Power Supply Circuit: <\/span> This circuit will provide 5 Volts to all the digital parts and LCD screen.\u00a0 The 10uF cap functions as a simple noise filter.\u00a0\u00a0 The battery connects to the input.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1370 alignnone\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/tach_clip_image002_00021.jpg\" alt=\"\" width=\"407\" height=\"275\" \/><\/p>\n<p><span style=\"text-decoration: underline;\">The Infrared LED Circuit: <\/span> Very simple circuit for the IR LED.\u00a0 The 150 Ohm resistor will limit the amperage that the LED will use and keep it from burning out.\u00a0 Note: Ohm\u2019s Law V=IR\u00a0\u00a0 if you are interested.\u00a0 This circuit gets +5V from the power supply you built earlier and draws 33 mA<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1371 alignnone\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/tach_clip_image002_00031.jpg\" alt=\"\" width=\"384\" height=\"259\" \/><\/p>\n<p><span style=\"text-decoration: underline;\">The LCD &amp; RPM counter:<\/span> This is the most complicated part.\u00a0 There are only 7 parts but there are a lot of wires.\u00a0\u00a0 Don\u2019t panic, it\u2019s not as bad as it looks.\u00a0 If you happen to wire it up wrong it will not damage anything.\u00a0 I even wired mine wrong the first time so just take it slow and check your work.\u00a0\u00a0 This circuit also gets +5V from the power supply you built.\u00a0 The PIC 16F628A needs to be programmed for this to work as well (explained later on in Step 4).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-1372 alignnone\" src=\"https:\/\/www.freemansgarage.com\/wp-content\/uploads\/2007\/08\/TACH1.gif\" alt=\"\" width=\"514\" height=\"575\" \/><\/p>\n<p>That is all for the electrical assembly.\u00a0 The only thing connecting these 4 circuits together is the power.\u00a0 I wired a switch in the battery leads to turn the tach on and off.\u00a0 I put the \u201cpower supply\u201d circuit and the \u201cLCD and RPM counter\u201d circuit on the same circuit board.\u00a0\u00a0 It is possible to solder the 16F684A direct to the circuit board but you MUST have it successfully programmed before you do so.\u00a0 I always use an 18pin socket so I can remove it if I need to.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1373 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/circuit20board1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><\/p>\n<p>If you are wondering where I got all the small colorful wire, I will tell you a secret to a nice supply of small wire.\u00a0 Find an old computer serial cable or parallel port printer cable that is no longer used.\u00a0 I buy these from garage sales all the time for cheap.\u00a0\u00a0 Cut the ends off and strip the outer cable off.\u00a0 There are at least 25 different color wires in there that are 6ft long and very flexible.\u00a0 CAT5e cable is absolutely terrible to mess with and it is really stiff.\u00a0 I do not recommend using that.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1374 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/wire1.jpg\" alt=\"\" width=\"800\" height=\"600\" \/><\/p>\n<p>Wire from an old Parallel Port cable.<\/p>\n<p><span style=\"text-decoration: underline;\">Step 4<\/span><br \/>\nProgramming the PIC16F628A<br \/>\nProgramming the PIC16F628A is very simple however you need a device called a \u201cPIC Programmer\u201d to do it.\u00a0 It\u2019s a small interface that will connect to your computer\u2019s serial or parallel port.\u00a0\u00a0 The PIC chip plugs into the programmer and you load the software (HEX file) into it from the computer. \u00a0\u00a0The manual for the programmer will tell you how to accomplish this.<br \/>\nFiles needed:<br \/>\nHex File &#8211; <a href=\"http:\/\/www.freemansgarage.com\/TACH.HEX\">TACH.HEX<\/a> (right click and save as)<br \/>\nIf you want the source code it is posted at the bottom of the web site.<\/p>\n<p style=\"text-align: center;\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1375 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/tach_clip_image002_00041.jpg\" alt=\"\" width=\"250\" height=\"167\" \/><\/p>\n<p style=\"text-align: center;\">Example Pic Programmer<\/p>\n<p>A PIC programmer cost about $25-$30.\u00a0 They come as a kit that you have to build.\u00a0 Some of them are already assembled but those cost more ($50+).\u00a0 Mine is called a PICALL programmer and it was $20 about 10 yrs ago <a href=\"http:\/\/www.picallw.com\/\">www.picallw.com<\/a>.\u00a0 It took me 2hrs to build and the instructions were very easy to follow.\u00a0 I am not sure if it\u2019s still available but you can use any programmer that supports the PIC chips.\u00a0 I have even seen them for sale on <a href=\"http:\/\/www.amazon.com\/\">www.amazon.com<\/a>.\u00a0 Just do a google search for a \u201cPIC Programmer\u201d and you will get a lot of results. \u00a0I also see quite a few on EBAY that are low cost.<br \/>\nIf you can not program your PIC, send me an email. I will gladly program anyone&#8217;s chip for free. All I ask is that you pay for shipping both ways.<br \/>\nI included the HEX file which is the software that you need to write to the PIC16F628A chip for the tach to work properly. When you buy a PIC programmer, it will write the HEX file to the chip for you. I also included the source code in case anyone wants to modify the software to suit their needs.\u00a0 I am not going to go into detail on how to code software for the PIC chip.\u00a0 There are many books and web sites that have information about how that works.\u00a0 The \u201cassembly\u201d language that the PIC chips reads is a \u201clow level\u201d language and is difficult to learn.\u00a0 I highly recommend using software like PICBASIC that will allow you to write code in BASIC, which is high level and very easy to learn.\u00a0 The PICBASIC software will \u201ccross compile\u201d your BASIC code into assembly and it will make the HEX file for you.\u00a0 It\u2019s much easier and is quite powerful.<br \/>\nThe software I wrote for the tachometer is simple and functions as follows:<br \/>\nThe screen updates the RPM every 1.5 seconds since that\u2019s how long it reads the sensor.\u00a0 The longer you read the sensor, the more accurate the RPM is.\u00a0 There is a trade off due to the math in step 3.\u00a0\u00a0 If you read the sensor longer, the resolution goes higher however the screen update gets longer which can be a pain.\u00a0 If you read the sensor shorter for example perhaps it\u2019s only .5 seconds, then you get a fast screen update but the RPM is low resolution which causes the RPM to count by 50\u2019s.\u00a0\u00a0 I tried to get the best of both worlds.\u00a0 Reading the sensor for 1.5 seconds, the RPM will count by 20\u2019s which is pretty good.\u00a0 It\u2019s stable and does not jump all over the place.\u00a0 The reason I used three slots instead of one was to slow down the \u201creal\u201d RPM of the wheel.\u00a0 I tried it with one slot and the wheel had to physically spin at 3000 RPM to read a 3000RPM heli rotor.\u00a0\u00a0 This made the tach vibrate and it was very noisy.\u00a0 Three slots caused the wheel to spin at 1\/3rd of its original speed and it was very quiet.\u00a0 When the tach is reading a rotor RPM of 3000, the wheel inside the tach is actually spinning at 1000RPM.<br \/>\nI gave my homemade tach to a buddy that flies all the time and he seems to like it.\u00a0 He has told me that its accuracy is perfect so far and it easily can read RPM up to around 6000.\u00a0 I included some additional pictures of the inside of the tach in case anyone is having trouble fitting everything inside.<br \/>\nStep 1 \u2013 The computer initializes and displays the welcome screen.<br \/>\nStep 2 \u2013 The computer will read the sensor for 1.5 seconds and count how many times the \u00a0\u00a0\u00a0slot goes by.<br \/>\nStep 3 \u2013 There are three slots on the wheel.\u00a0 The computer has to do some simple math to convert the number from step 2 to RPM.\u00a0 It will divide the result by 3 and convert 1.5 seconds to minutes to get RPM.<br \/>\nStep 4 \u2013 The result from step 3 gets sent to the LCD screen for you to see.<br \/>\nStep 5 \u2013 Repeat Go to Step 2<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1376 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/tach220low20res1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1377 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/tach320low20res1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1378 size-full\" src=\"http:\/\/45.79.146.68\/wp-content\/uploads\/2007\/08\/tach420low20res1.jpg\" alt=\"\" width=\"700\" height=\"525\" \/><\/p>\n<p>Several assembly tips:<\/p>\n<blockquote>\n<ol>\n<li>Too much heat from the solder iron is bad.\u00a0 15-20 Watts is plenty for this project.\u00a0 When soldering the PIC chip, be quick about it and do not let the chip heat up too much or you may damage it.\u00a0 I recommend using an 18pin socket so you can avoid soldering the PIC at all.<\/li>\n<li>Too much solder is also bad.\u00a0 Have a solder sucker nearby if you use too much.<\/li>\n<li>Pre \u201ctin\u201d the wire ends with solder.\u00a0 This helps tremendously when soldering wires together.<\/li>\n<li>When you finish the shutter wheel, try it out on the motor before you glue it.\u00a0 Make sure it\u2019s on the shaft straight with no wobble.\u00a0 (hook up a battery to the motor to test it out)<\/li>\n<li>Measure your LCD screen and make sure it easily fits in the hole you made in the project box.\u00a0 It does not need to fit tightly and you will epoxy it in place when finished.<\/li>\n<li>Optional: Use a breadboard to assemble the circuits first.\u00a0 It\u2019s an easy way to build the circuit without using any solder.\u00a0 Breadboards are cheap and are a very good tool to have on the workbench bench.<\/li>\n<li>Buy extra parts (resistors, diodes, etc).\u00a0\u00a0 You might accidentally destroy something or lose it.\u00a0 These parts are cheap and it will save some of your sanity.<\/li>\n<li>Don&#8217;t use anything too shiny for the shutter disc. I have had reports that the sensor has trouble &#8220;seeing&#8221; the IR LED if the disc is too shiny.<\/li>\n<\/ol>\n<p>If you need help email me but please do not ask me to build one of these for you. I only posted this information to provide you with a fun way to make your own heli tachometer.<\/p>\n<p>Source Code for the PIC Chip (right click and save as):<\/p>\n<p><a href=\"http:\/\/45.79.146.68\/stuff\/tach.bas\">Tach.bas<\/a> &#8211; This is the PIC BASIC Source code.<br \/>\n<a href=\"http:\/\/45.79.146.68\/stuff\/TACH.ASM\">Tach.asm<\/a> &#8211; This is the Assembly Source Code.<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"<div class=\"mh-excerpt\"><p>The Tachometer The tach will measure RPM of an R\/C helicopter rotor using a shutter effect by rotating a disc at a known RPM and <a class=\"mh-excerpt-more\" href=\"https:\/\/www.freemansgarage.com\/index.php\/2007\/08\/07\/homemade-optical-tachometer\/\" title=\"Homemade Optical Tachometer\">[&#8230;]<\/a><\/p>\n<\/div>","protected":false},"author":1,"featured_media":856,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[4],"tags":[],"class_list":["post-141","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-projects"],"_links":{"self":[{"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/posts\/141","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/comments?post=141"}],"version-history":[{"count":5,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/posts\/141\/revisions"}],"predecessor-version":[{"id":1479,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/posts\/141\/revisions\/1479"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/media\/856"}],"wp:attachment":[{"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/media?parent=141"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/categories?post=141"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.freemansgarage.com\/index.php\/wp-json\/wp\/v2\/tags?post=141"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}