i built a test box to test electronic dashboards on countax mowers but need help

[petehall347]

ok so i built a box to test the electronic dashboards on countax ride on mowers , all works fine and can test all functions with the aid of switches buttons and lights . only thing is the engine rpm that i cant check so need some sort of oscillator i can put together with parts from my stock . and need confirmation where to connect it to on the board . engine kill is short to ground and with it being connected to the coil i presume the signal comes from there .
thinking will need 1000 to 3000 rpm variable .
will post pics of my build later .

[stj]

Re: i built a test box but need help

never presume - scope a mower if you can.

[petehall347]

Re: i built a test box but need help

it has to come from the coil . i know you can program these boards for 1 or 2 cylinder engines .. if it came from the alternator it wouldn't matter . i could do with an oscillator that equates to between 1000 and 3000 rpm . i dont know what frequency it relates to .
ok i worked it out i think .. 16.66 hz to 50hz .. but its 4 stroke so those figures need dividing by 4 . or does it need multiplying by 4 ?

[redwire]

Re: i built a test box but need help

3,000 RPM 2 cyl, 4 stroke is 50Hz at the coil
1,000 RPM 2 cyl, 4 stroke is 16.7Hz at the coil.

Assuming it's not a "wasted spark" ignition system that uses one coil with two HV outputs for 2 cylinders. Or maybe this is a magneto system?

You can make an oscillator with a 555 or a couple transistors but most tachs are looking for a HV spike or several hundred volts to trigger, not 12V pulses.
So you'd need to add an inductor to make the HV spike.

[petehall347]

Re: i built a test box but need help

i expect the safest way is to try low voltage spikes first and see if it works . no way i want to probe a coil with my multimeter as have killed them this way . taking my scope to one isnt going to happen . i could take a spare scope that might not even work as has been left not used for years .saying that my bench one hasn't seen power for a long time .
will see if i can trace the route to the mcu from where the signal goes to the board

[petehall347]

Re: i built a test box but need help

ok as promised a couple of bad pictures .. ignore the rough and ready look .its a prototype

[stj]

Re: i built a test box but need help

lol - thats quite a mix of led mounts
have to start calling you Mustie2 if your gonna make a thing of small engine repair

[petehall347]

Re: i built a test box but need help

everything apart from a dc socket that i bought is from what i had lying around here that i got off freecycle and all brand new in packets . as far as i know its the only oms diagnostic box in existence . oms is onboard management system . its made my job loads easier . next upgrade will be a 16 pin socket so i can then make the various leads for other boards . thinking of using car obd stuff for that .