Putting the cap where it is at in the circuit I posted keeps the transistor on as long as the pulses keep coming at a few rpm. The other puts out a pulse each time the plug fires.

 

ok that sounds like what i need.
i should have most of these parts. will any 2N transistor work? i dont believe i have that exact part.
and on the zener diode, i see you have a 10V, i have 5V zener's here, is it possible to use those in a different arrangement?


also, i know you mentioned about not knowing the amount of turns needed. saying that, is the output of the circuit limited in any way? or is it linear with the input just smoothed out?
if its varying voltage from the input, could we use that 2nd schematic i posted with it? ive tested that and it works nicely and has a 0-30V usable input.

thanks for the help, getting close!
taylor

 

i should have most of these parts. will any 2N transistor work? i dont believe i have that exact part.

It needs to be a MosFet transistor.

and on the zener diode, i see you have a 10V, i have 5V zener's here, is it possible to use those in a different arrangement?

You can use 2 in series.

i know you mentioned about not knowing the amount of turns needed. saying that, is the output of the circuit limited in any way? or is it linear with the input just smoothed out?

It is just on ( 0 volts) when the engine is running, or off (5v) when engine is not running. Are you looking for a linear output based on RPM?

if its varying voltage from the input, could we use that 2nd schematic i posted with it? ive tested that and it works nicely and has a 0-30V usable input.

Not sure which one. Most of those output a pulse when the plug fires and the micro calculates RPM based on the number of cylinders.

 

will any N channel mosfet work? like these?
http://www.radioshack.com/search/index.jsp?origkw=mosfet&sr=1&kwCatId=13384949&kw=mosfet&pg=2

thats the goal, i dont need linear based output now. On/off will be perfect.

hopefully can get this worked up today. thanks for the help so far!

 

also, could you clarify your sim drawing?
confused on the ground and voltage rails.
http://forum.allaboutcircuits.com/attachment.php?attachmentid=59238&d=1378842988

i guess the lower rail is the ground, but whats that gate tag, and what component is V1? and is there a +5V for the transistors anywhere coming in?

sorry for the beginner questions!

 

i was under the impression that a magnet wasnt required? that the dc current gave enough radiation off for the hall effect to determine the current?

like this sensor:
http://www.dfrobot.com/index.php?route=product/product&product_id=580#.Ui5GTz-wUec

The current in the secondary circuit is tiny - a few ma. plugs leads are also notoiously leaky and you run the risk of frying something with a bad lead or damp weather. You don't really need an inductive clamp, just wrap a few turns of light guage insulated wire around the plug lead and you will get a good pulse. Ground one end of it to protect your circuit.

Another possibility is to use an old neon from a phase tester.It will also light up with one wire tied to a plug lead and a 5 M Ohm resistor going to ground on the other. After that you could have a completely isolated circuit using an LDR or some other kind of opto-coupling.

 

i guess the lower rail is the ground, but whats that gate tag, and what component is V1? and is there a +5V for the transistors anywhere coming in?

Yes, the lower rail is ground.
V1 is just for the simulation, it represents the voltage picked up by the wire wrapped around the plug wire.
The 5 volts for the FET is shown as a battery on the right.
Use the NTE491 in your link.
The gate tag is just so you can see what point is plotted in the simulation. If you look at the waveforms you can see they match the tags.

 

thanks for the replies ronv!
they didnt have that exact mosfet in stock at my local radioshack.
i picked up these though:

2N2222
2N3904
2N4401
IRF510 Power Mosfet N channel, 60V
TIP31 NPN

can i substitute any of these in place of the 2n7002? hopefully so.

thanks again

 

IRF510 should work.

 

ronv,
i got the circuit up and going, and due to it being real late, wasnt able to test it on my refereed vehicle, a single cylinder motorcycle. So I put about 15 wraps around my V8 truck engine plug wire (after the coil) and I'm still getting 5V reading when running/off.
Put a multimeter on the input of the breadboard after the wire wrap and when running i'm getting .055VDC. I'm also not grounding one side of the wire wrap, its just a lead off the breadboard wrapped on the plug wire.
What do you think the issue is? I'll be able to test the motorcycle tomorrow during the day, but I wonder if the firing order of the truck, possibly not giving enough pulses a second, is causing the issue?

 

I was able to test it on a single cylinder engine a few minutes ago and i believe its working now. wiring up a version in my Arduino, so hopefully will have a working prototype up here pretty soon.

 

everything is working as your sim showed.
THANK YOU! awesome help!

 

Glad it works. Now we know. Thanks for being the test bed.

 

this idea is running great so far, but i'd like to improve it even more and slim down the package.
my idea now is to take this basic principle and eliminate the wire wrap and run from the eletrical source of the magneto/CDI.
this is a small stationary water pump. the magneto system goes to a cdi and runs the spark plug, and there is also an accessory rail to go to a stop switch, lights, ect.
measuring off the accessory rail. i'm getting a Pulsed DC signal. and its going from around 15V on idle, to when the pump is turned on faster reading around 80V.


Obviously this is way above voltage of logic level. So, I've been looking into a device to separate the two, yet still act as a gate between them.
Looks like an optocoupler could be what i need?
http://www.youtube.com/watch?v=uRX0OwWjKXA&feature=player_detailpage#t=66

Also, I think that the incoming signal needs to be conditioned and smoothed out, else the pulsed DC may switch the optocoupler on/off rapidly and cause issues?
Could this be remedied with a simple higher voltage cap on the front end of the optocoupler?

so maybe 0-100V input-> smoothing cap-> optocoupler-> *CURRENT WORKING CIRCUIT*. ?

Let me know what kind of ideas you guys have.
thanks as always.

 

I'm a little confused about a water pump from a CDI. But if the signal is "real" and not "noise" you could just add a cap, say .01Ufd. @ 100v from the signal to the input of the existing circuit.

 

i dont have a scope yet, trying to get one soon. but i believe the signal looks something like this, a bit noisy, but also pulsed. let me know if that helps.

 

I don't think it will hurt anything to try it. If it is just noise it may not work, but if there is enough energy it will.

 

JBernard,

This is good that you are trying to work out the problem for yourself. That is how you learn.

The first circuit on the paper looks to be doomed to failure by the 100Uf capacitor, which will short out all of your signal, since the capacitor will not charge fast enough, it is too large. That part of the circuit will have a time constant, RC of 5000 ohms times 100uF which is .5 sec. This means that in .5 sec, the input voltage will only reach 62% of what you put in. the problem will be that the ignition pulses only last for a few microseconds, IE the cap will kill the whole signal.

The second circuit has promise. You might want to consider shorting out the reverse voltage (Which could kill the transistor) with a reversed diode across the two series diodes.

Maybe you will want a higher value of series resistor, than 2.2K if the coil puts too much current out, but the power here should be small with loose coupling.

Cutting a sensor off of a timing light does sound like a good idea.

Bob

 

Bobweb1234, thanks for the compliments, much appreciated. always love learning!

on the first schematic, i believe that cap is a 100nF after realizing how big 100uF is and that i couldnt find any with normal lead spacing. i took a few ideas from that circuit but didnt end up using it. it was mostly based around RPM which i didnt end up needing right now.

I researched the timing light a little bit, and came to the conclusion that most use a hall effect sensor housed in a magnet all enclosed in a clamp type terminal. Like a Fluke DC Ammeter. This method could probably work if i'm dead set on a clamp/wrap type meter on the spark plug wire that is cleaner than just a wire wrapped around several times.

But i'm a bit confused on the optocoupler now. I think this could be my best bet bet as it would fit to an extremely wide voltage range. i need 0-200V to be on the overly safe side.
What I'm hung up on is how to put the optocoupler 'in-line' with the circuit. it seems it wants an input and a ground on each side, and I'm trying to get it to be just like an input/output instead.

Here's a quick breadboard layout of what i'm thinking *may* work but i'm probably way off on the high V+ side?

edit: seems i cant get a good resolution so you can see the arduino hookups
they are:
red - +5V regulated
blue - Analog0 input (to sense when gate is on and +5V is detected thus senses an 'ON' state
blk - gnd


here are some circuits of the optocoupler:

Thanks for the help guys!

 

really hoping the optocoupler idea will work for what im trying to accomplish.

also found out Analog Devices has a product out that is way better than the traditional optocoupler. inexpensive, faster, less power, looks promising:

http://www.analog.com/en/interface-isolation/digital-isolators/adum1200/products/product.html