Ignition tach using ebay module

[6PTsocket]

https://www.ebay.com/p/0-56-Digital-Red-LED-Frequency-and-Tachometer-Rotate-Speed-Meter-DC-12-24v/1131861035?iid=280903275997


I want a tach for my chainssw that revs up to 12500 rpm and higher. The better ones are 100 bucks and up. I found these 5 digit tach modules on ebay that seem to have a lot of flexibility.  There is quite a bit of info in the ad. Apparantly they can read pulses/ sec for a freq.meter or pulses/min for a tach. They also have an adjustable ÷ by function for multi cylinder engines. The one  I linked  to  runs on 5 volts but there are 7-12 and 12-24 volt powered units.  The displays are red or blue .56 leds. There seem to be others without a case that have a smaller display. They are supposed to be good to 99999 rpm. I want it hand held and probably wireless. If I get the 7 to 12 volt I am not sure whether a 9 volt battery will handle tha display very long. LCD would be better but it is LED and cheap. My other question and bigger issue is input conditioning. There are two sensitivity settings 3 to 30 and 30 to 300 volts. I have looked at the front ends if tach circuits I found on line. Can I just connect an antenna to a 1k resistor that goes to an input shunted with a pair of back to back 5 volt zeners? They  show  transisistor inputs as an option but I don't know if that is necessary. Any design advice on front end design and  power supply suggestions greatly appreciated. I am sure I can get it to work but I would like to select the easiest  one to power up and not blow up the tach with ignition spikes before getting the bugs out. Thanks.

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[langwadt]

how about hacking a bike computer instead? https://www.instructables.com/id/Tachometer-made-from-a-bicycle-speedometer-cycloc/

[6PTsocket]

how about hacking a bike computer instead? https://www.instructables.com/id/Tachometer-made-from-a-bicycle-speedometer-cycloc/

There is no convenient place to stick a magnet. The speed is too low.. i want to run off ignition pulses. Even the freq function on my dmm wirelessly reads off  ignition but is reading pulses per sec, not per minute. The tach modules are around 10 bucks. I want to make one of them work. There is no cheaper way you can get 3 refreshes per sec. Look at that spec sheet.

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