 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Electronics : Car RPM meter for mill?
| Author | Message | ||||
| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, Cleaning out my study (there has to be a first time for everything!) I found an old RPM, tacho, water temp setup. Sorry, do no longer know the brand of car it came from. Has three inputs, plus, ground and sensor input marked 'S'. Does it come off the ignition or Hall sensor or some opto system? Goes to 8000 RPM but can it made to go to a reasonable mill RPM figure? Dr Google is no help here. Can see two green (marked MKT1822 wire wound?) and yellow rectangular (?) things, electrolytic caps and resistors. Marking says "VDO Australia 12V". What are my chances to get this analogue display working in addition to my digital recording ex Glenn? dom Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hi Dom As it seems to be an older 12 volt tacho, the sensor wire would operate from the hall sensor or points opening. As such the sensor does not draw much current, only a pulse, barely readable on most multi meters. It is this pulse you would need to replicate. Some tachos are designed for 4, 6 or 8 cylinders, or have a switch on them to pick a cylinder number. If you can fit something to the rotor that will enable you to get a pulse, say 10 or 20 times a rotation then you will have some success. Just work out the ratio of serrations to the equivalent engine RPM turns for the rotor speed. ie, 1 rotation of a 4 cylinder engine is two pulses, 8000 pulses for 4000 rpm, a mill at 400 RPM would need 8000 pulses (20 tabs) to read 4000 on the tacho, take off a zero, 400 RPM An old type magneto with a serrated hall effect plate (magnets ??) matched to the rotor might do the trick, but you will probably lose the signal when the mill is on top of a 20 meter pole. As I said the signal strength required is very minimal. Getting the required pulse strength each pulse would be a matter of trial and error, what works at 2 meters will die off at the top of the pole. Long term success would seem to be limited.... But you never know, some of my crazy contraptions have worked beyond expectation. Mark |
||||
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
From what Mark says on whats required for a input signal, there is likely no reason you could not generate the signal from the mill AC, basically the same way as Glenns circuit do, by using an opto coupler and 12v on the transistor side of the opto, you might need to add a divider chip like a 4017 to adjust the input pulses to suit the taco. For example if you had 36 pulses from the mill and you needed 20 pulses for the taco per mill rev, you wont exactly get it, but dividing the 36 by 2 will give you 18 pulses per rev and might be close enough. Pete. Sometimes it just works |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks Mark and Pete. Have to ask Dr Google for the purpose of a 4017. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Big mistake trying to find application notes for the LM4017 to learn more electrickery! Have learned now not to click on offers of application notes but to contact manufacturer's web sites. Have managed to download websearches, a browser hijacker, a register cleaner and three or four other programs, most of which I could delete, but not websearches via Windoze Uninstall. Anyway, I am onto it with malware programs and with the help of Dr Google'sdvice. OK, let's talk Volts: I feed the RPM meter with 12V. The DC pulse comes in at 12V, no problems as I know by now to reduce the voltage to 5V for the Picaxe via voltage dividers. Anything else? Can I then simply use the COUNT command on the Picaxe to get the RPM? Any filtering via caps? Let's pool our ignorance! Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Dom, Im a little lost with your reply, should you want a good data sheet search try this site. http://www.datasheetcatalog.com/ Its the main site i use for data and should give a hint to how good it is. A 4017 chip is a decade divider chip, meaning it can count to 10 and repeat, but it can be selected to count to any number between 0 and 9 ( = 10) The last part of your reply im lost with regardinging voltage dividers and picaxe, i fail to see where a analog rpm meter and Picaxe cross paths, or how they both relate to this thread, my suggestion was to take circuit design from one project (Glens picaxe input) and use it for the analog meter, but not intergrate the two together as a combined project. Again happy to help and you know where to find me Pete. Sometimes it just works |
||||
 Print this page |
