I picked up one of the BI-Tech range yesterday for £2.49 so guess they are clearance items, reason was they read revs up to 3600 rpm ir at least they say they do. I doubt if the mph or kmh readings will be of much use though.
May just be trying it out on my that spindle soon with the VFD drive to at least allow me to calibrate it somewhat.
Thought it may be of use to others to know!
Cheers
Adrian
You could use the rpm/mph scales for other things by setting the wheel circumference in the computer appropriately. I'm thinking if you set it to 1.667m (maybe move the decimal point to fit the computer's range) it will display 10's of revs/minute while in the kph mode. Inputting (workpiece diameter) * pi * 1000/3600 would give surface speed... as the circumference is fixed it's not too useful for anything but a finish cut.
cheers Guy
I built an anemometer last yeart around one of these bike computers- worked great-but the reed switch sensor failed after a month or so on the roof, I guess due to fatigue of the reeds. it's now shoved to the back of the bench pending re-design. So I would recommend not spending to much time on the sensor mounting etc. the variables you can program ( with patience) do make these useful gadgets though, and initially the rpm indication was spot-on against the works calibrated tacho. Mark G
Yes I guess that the reed would only be good for 10's of thousands of switches. I wonder if it would be possible to switch an open collector transister using a coil diode and cap from the magnetic pickup. Or using an opto sensor and LED, but it does mean another supply. I guess it is a try it and see one when my own fails!
Adrian
Why not use a Hall effect device in place of the reed switch? There are a large variety of them around that would do the job.
Regards, Tony
In article , Tony Jeffree writes
See the Woking Precision Models kit:
The hall effect switches may well work. Well it obviously will work if I use something like a 9v pp3 battery supply for the hall sensor.
The bike computers are approx 1.5 volts across the input pins, and was just wondering if a simple pick up coil and diode could drive the base of a transister directly to switch in on and act like the reed relay.
If used in the workshop then any supply would not be an issue, I guess.
Adrian
I have been looking into the solid state triggers as I need to fabricate an ignition pickup for an electronic ignition system (triggered 4 times per revolution from cranking speed up to 6000rpm). If I outline my current state of ignorance then maybe someone can point out whether I am on the right track. As far as I can tell there are two main types of trigger, one depends on a magnet going past, and another has a magnet in it and relies on a lump of steel/iron going past to cause a pulse (I think this type is called inductive). Some are powered, some just have a coil to give a pulse, and one I have seen has a coil and a powered op-amp chip on board.
I think the Hall Effect ones give a fixed voltage pulse, whereas the coil type give a bigger and bigger voltage the faster they are triggered.
For ignition I need something fast switching, weather proof, and ideally triggered by metals rather than magnets - so I was thinking of an ABS sensor from the scrapyard. I don't know if these are Hall effect or not, but they must have the magnet inside.
Am I on the right track with this, as I haven't found any useful web pages explaining this lot ?
Steve
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