Guest Riker Posted November 18, 2003 Share Posted November 18, 2003 The winter is knocking, it's going to be a loong one, so I need to keep myself busy.. I decided to make a digital speedo, a idea crossed my mind when I smashed my buzzer this morning...i picked up the led display and thought - they! That would look cool in my car! So I need some basic advices, tips, directions... My car has a needle ona a tacho, and the tacho's cable goes into gearbox..so that's how it measures speed. So, how can I make a speedo? 4 digit led display? Can I make a little sensor into the gearbox that monitors the speed, or maybe something near the wheels...I really don't know what's the easiest way, so please help. The other thing is - refresh time. My friend has a car with digital speedo, and I really don't like it because it refreshes really slow, maybe every 1.5 secs or something like that...slow. OK, after the speedo...is it a problem to make a rev counter, also digital...with a sweep effect? Quote Link to comment Share on other sites More sharing options...
Guest LedFoot Posted November 18, 2003 Share Posted November 18, 2003 Hey Riker, You can get a pulse counter (Hall effect sensor) that threads onto the back of your speedo between the speedo and the cable. Check out a place that stocks Siemens or VDO automotive equipment. Take the output of this into an ADC (analog to digital) port of a microcontroller and you can count and average the pulse rate which will give you speed or rpm depending on the application. Then code the pic to run an LCD or dot matrix display (whichever you think looks better). Just make sure you choose a display that can handle automotive temperature ranges, at work we normally use -40 to 120 deg C for North America. For the micro I suggest using a PIC (http://www.microchip.com) They're cheap, easy to use and more importantly their development tools are free! (I think!) also their programmers are very cheap as well, you can get out of it for around 20-50$ US. Other than that you may be able to pick up a kit from tandy, radio shack or some other electronics store that already does it. All you would have to do is solder it all together. Have fun with it, if you've never done anything with electronics before, it's actually a pretty good project to start on, not too easy but not too difficult! Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted November 18, 2003 Share Posted November 18, 2003 You are going to need quite an expertise in electronics to undertake such a project. My guess would be, that since you are asking this question, you do not have such an expertise. There are a couple ways to go about this. You could make a sensor (located at the flywheel or distributor) to pick up a pulse for every RPM. This pulse would need to go into a logic circuit that would calculate the speed based on RPM and gear ratios and then through another circuit to turn that data into a numerical display on the LCD panel. This way would be good because then you could run your Tach off the same setup. You could make a sensor to pick up the rpm of the cable from the transmission and use that to calculate speed then through another circuit to turn that data into a numerical display on the LCD panel. And finally you could make a sensor at the wheel or axle or driveshaft to pick up the rpm of either and use that to calculate speed then through another circuit to turn that data into a numerical display on the LCD panel. I suppose you could also use a single sensor at one of those locations and send the data into an onboard computer and use computer software to process the data and send the output to a display. (This is something that a computer software nut like myself might do ) Keep in mind though that each of these suggestions if very overly simplified. You may find it to be much easier, cheaper, and less time consuming to buy a digital setup. Quote Link to comment Share on other sites More sharing options...
RPMS Posted November 18, 2003 Share Posted November 18, 2003 Something a lot of sportbike riders are doing is using an LCD speedo from a bicycle! Some of them go up to 180mph, have additional trip odometers (think - Distance Between Oil Changes), and best of all, they're under $30. Not the LED's you're thinking of, though. Quote Link to comment Share on other sites More sharing options...
Trevor Posted November 18, 2003 Share Posted November 18, 2003 If you are really into scrounging JY parts (like me) there are electronic speedo sending units on Nissan transmissions as far back as 1984. i.e. 300ZX digital dash. '84-'86 has a short cable and the VSS in the engine bay, '87-up is on the tailshaft housing. If you are using a F-body transmission, Firebirds switched to electronic speedos in '86-up and Camaros in '92. The sending unit is still mechanically driven by a gear on the output shaft. Some transmissions use a Hall-effect magnetic sensor, I think the 4L60-E doesn't have the gear. I am currently working on a way for the late Camaro transmission to interface with the Nissan digital dash. The gage makers' website, and Hot Rod mag. says most oem VSS signals are sine wave, while their meters prefer square wave, but aftermarket gages will work with either one. Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted November 19, 2003 Share Posted November 19, 2003 For an easy to adapt bar graph display, look at the LM3914 IC: http://www.national.com/pf/LM/LM3914.html A variable voltage input drives a series of 10 LED segments. The chips can be chained together so you can have displays of 10, 20, 30 etc segments. A rotating cable could be attached to a little electric motor, so it generates the variable voltage in relation to speed. The bar graph display is calibrated to go full scale at the max speed or rpm. Quote Link to comment Share on other sites More sharing options...
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