Small digital tach

[Vietti]

I am looking for a small, self contained digital tach, to mount on a hit and miss engine model. Hopefully triggered by a rotating magnet.

Does anyone know of such a critter??

Thanks, John

 

[Scott_M]

I put one of these on my lathe.

DIGITEN 4 Digital Red LED Tachometer RPM Speed Meter + Hall Proximity Switch Magnet Sensor NPN for Lathe Conveyor Belt: Amazon.com: Industrial & Scientific

It might be big for a model but works great on the lathe.

Scott

 

[Poppy Ott]

I put one of these on my lathe.

DIGITEN 4 Digital Red LED Tachometer RPM Speed Meter + Hall Proximity Switch Magnet Sensor NPN for Lathe Conveyor Belt: Amazon.com: Industrial & Scientific

It might be big for a model but works great on the lathe.

Scott

As you say, this may be too big for what Vietti has in mind, but hey work very well. I have three of them, one on each metal lathe and one on the wood lathe.

 

[GailInNM]

I use the inductive pickup tachometers for outboard motors and other small engines. There are a variety of then available on both E-Bay and Amazon starting at about US$12. Here is the one I have been using for several years. It is programable for 2 & 4 stroke engines so can be used for wasted spark or camshaft driven ignition. It is self contained with internal battery. When the engine is not running it can be set up to display the total running time on the engine. No wiring. Just position the pickup within about 1 inch from the spark plug wire.
amazon.com/Timorn-Replaceable-Waterproof-Tachometer-Motorcycle/dp/B0756VGDTC/ref=sr_1_15?crid=19BCIJW0W981Q&keywords=OUTBOARD%2BMOTOR%2BTACHOMETER&qid=1644422691&sprefix=outboard%2Bmotor%2Btachometer%2Caps%2C105&sr=8-15&th=1

Gail

 

[Vietti]

thanks for the replys. I was hoping for something smaller as you say. May buy one as described to mount on a machine tool. Maybe someone yet will come up with a suggestion.

John

 

[Gedeon Spilett]

look at this one, Arduino based with Hall sensor, simple and cheap to make.
https://makersportal.com/blog/2018/...effect-sensor-to-measure-rotations-from-a-fan

 

[Vietti]

Gail,

I tried one of those types on another engine I built, a Hermes from the UK. Sort of worked but was wildly inaccurate. I'm running small home made mags and that maybe part of the problem.

I may use one of the first suggestions and make a separate job box hook up and try a small hall sensor ala a CDI ignition system.

John

 

[Tom Watson]

Go to the hobby shops on line that sell model aircraft stuff. You can get some very small digital tachos there. some need a contrasting stripe on the flywheel.
https://www.towerhobbies.com/product/micro-digital-tachometer/HAN156.html

 

[methuselah1]

You could do a lot worse than looking at Minimag Co's offering... It's microscopic!

 

[Peter Twissell]

Cheap bicycle speedometers can also be adapted to use as a tacho, but don't work well at high speeds.
Might be ok for a hit and miss.

 

[mgbyrne3]

You might do a search for digital tachometer on EBay and/or Banggood.com. There are several varieties offered.

I wonder if a reed switch would be less sensitive to magneto generated EMI than a Hall effect sensor.

 

[Scott_M]

I swapped the NPN Hall sensor for a NPN proximity switch and just used the big knurled nut for back gear as a target.

I did not want a magnet in there to attract chips. This works well.
Vietti wanted a magnet for a trigger. There are different ways to trigger, but the display is still kind of big.
I wonder if the circuit could be gutted and used on a smaller 3-4 digit display?

Scott

 

[Vietti]

I was watching Ghosty's video on the Tiny Super. Reminded me some CDI units have a tach output and a small tach. Could one of these be made to work without the whole CDI unit? I'm running a magneto.

 

[Peter Twissell]

Any ignition signal can be used to trigger a tacho. If you have access to a low tension signal (e.g. points in a conventional coil system, or the trigger signal from a CDI sensor) it can be connected direct to the tacho input.
If you only have access to high tension (e.g. spark plug HT lead) then a few turns of wire around (but not connected to) the HT will also provide a trigger.

 

[dazz]

Hi
I retrofitted digital tachos on both of my lathes. The Denford Viceroy fit is documented here. These tachos are smart enough to change the sample / update time with RPM. They provide a good read out at all rpms.

 

[cwelkie]

Vietti - One option would be to try a "Tiny Tach" or similar. They use an induction pickup from the spark plug lead (just a couple turns of small gauge wire). I don't recall if 'Tiny Tach' has a single cylinder option or not ...
If this is going to be on a hit 'n' miss engine a digital tach might be challenged with the constantly fluctuating speed.