How would I go about amplifying the AC current reading that I'm picking up from the outside of a spark plug wire. I'm building a tachometer.
I've considered a transformer then adding a rheostat for calibration.
How would I go about amplifying the AC current reading that I'm picking up from the outside of a spark plug wire. I'm building a tachometer.
I've considered a transformer then adding a rheostat for calibration.
I should add, it's 1 cylinder.
Isn't that just a simple induction sensor clamped to the spark plug cable?Originally Posted by KG4CGC
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Yes, and one would need to step up and condition the voltage - rather than the current - to get a usable reference. Something like a JFET would work nicely without excessively loading the pickup coil and reducing its output. For TTL gating purposes you're aiming for 4.5-5.2v on peaks.
"Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."
Add turns to your pickup inductor.
Assuming you're not using a sealed unit. Some of the setups built for the auto-repair community cannot be disassembled for modification. I have an old Sears diagnostics meter that includes a tach function and most of my motorcycle ignition systems don't generate enough high voltage to get an accurate reading. I had to go to a "Daytona" brand accessory digital tach (which triggers off the coil primary; switched 12v) in order to get a usable low-RPM reading for purposes of carb synching, idle-mixture settings and so forth. Frustrating, as the Sears unit's pickup merely clamps around the #1 plug wire...and I had to add a pigtail to the ignition circuits of each bike where the Daytona will be used.
"Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."
Ah, I'm using coiled wire. Insulated probe wire.
Toroid?
No, but there's an idea! Simple and I have a couple of rings in the parts bin.
Basically, I wrapped the spark plug wire and tried a few of the settings on my DMM to see what I would get. I can build this for zero dollars just from parts I have. I just have to figure out mounting the meter and weather proofing. I have some meters that were passed on to me from an amp builder who got outsourced from his regular job. After I get the electronics figured out, (with help from you guys:) ) I just have to wire up some lighting for night use.
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