I would like to add a tach. to my old truck. 1953 M37. I want it to be a NeoPixel that tells me when I've hit 47mph. 'Cause that's where the RPMs top out and I'm tired of looking down at the speedo.
The part of this project I'm unsure about is how to sense engine RPM with my Arduino. Its tough to google this kind of thing 'cause the "internet noise" around it is so huge. Every tach. manufacturer does it, but I've never been able to find out how they are dealing with the signals.
And this one is a little strange because the truck is 24V and all the wiring is shielded and waterproofed.
Right now the idea is to tap into the primary side of the coil power and do some signal conditioning. I'm not experienced in circuits so if there's a simpler way, I'm all eyes.
Right now the idea is to tap into the primary side of the coil power and do some signal conditioning. I'm not experienced in circuits so if there's a simpler way, I'm all eyes.
Can you get access to anything which is rotating at engine rpm (or some fixed relationship to rpm)? You could then use a hall sensor or optical sensor instead of getting the signal from the ignition.
Where do you point the timing strobe light, to see TDC, when you set the distributor timing? Can you attach a magnet?
I've been chewing over the same thing. I never liked the visual sensors 'cause if things get dirty, and on this machine its going to happen, you loose your signal. Magnetic sensor? Possibly, but then its all about finding a place to put it.
The nice thing about using the ignition wire is that, once the electronics are sorted out, it's pretty easy. And, the wire runs right across the top side of the firewall. Making it easy to access.
I'm using something far simpler on another circuit. Revcounters always did. A diode and a handful of resistors and capacitors to smooth and reduce the spikes off the LT coil as you suggested and a zener clamping it to sensible limits. Worked okay up to 12000 rpm ( my Vtwin sportsbike)- beyond what an Arduino can cope with.
To be honest I was using far simpler chips, too - all analogue. But that was many years ago when the LM2917 FtoV convertor feeding an LM3914 bargraph was clever. Many consider analog to be old-tech nowadays and with the Arduino being so cheap and adaptable I can see why you're looking in this direction... but there are always other simpler possibilities. Let me know if you want me to share some of these old-tech ideas?
Having said that, with your 5kHz maximum revs Arduino will cope no problem. And if you wanted to do clever things like record performance to an SD card, add fancy gadgets etc, stick with an Arduino.
However, I found my in-car Arduino project froze/died/lost its way until I seriously addressed the horrible electrical conditions of so-called 12v automotive systems. Zeners are okay if you're as old as me and revert to what you knew then but these newer TVS diodes are brilliant - for my in-car project they were an absolute must, as are decent sized smoothing capacitors (uprate to at least 50v, no less for HGV 24v systems) and this was required on the supply line and also on the signal lines. I found all I needed to know here in the forum. That settled it all down and its been running continuously for several months now without a glitch.
Spikey things them alternators!
@lancsdude Its all for fun. I program NeoPixles all the time so I figured if I could put one in there it would be neat. I'm also thinking about drawing an analog tach on a little OLED display and reflecting that at me off the windshield. Donno' how to do that, but it would be cooler n' heck to make a HUD for the old thing. People do make them so it must be possible.
@JohnLincoln I'm already back in time! If I hit 88mph I'll know, the crankshaft will be about a mile behind me!
I'm holding off for a bit 'cause I currently don't have a shop big enough to bring it inside and the temp dropped below freezing.
I'm leaning toward making up a little "box" that I can hook to power, Gnd & the dist. wire then have that give a 5V square wave.
