Pulse generator positive negative waves?

After another sleepless night in a series of hellish weeks trying to start my 85 xr600 I've built a CDI from a kit.

The kit requires a POSITIVE pulse from the trigger coil (pulsegen) to switch an SCR and dump the capacitors (charged by the stator) into the ignition coil to stepup and spark.

The CDI circuit has inputs for : black/red stator wire, kill switch, ground, trigger.

Problem is the trigger input is 1 hole but the pulse generator has two wires which I'm pretty sure cant just be twisted together.

So... CDI connections

Opt 1

Blue/white from pulse gen to trigger input. Green/white to ground (pulsegen already grounded in engine..)?


Blue/white to trigger, green/white to stator wire and kill switch?


Green/white to trigger, blue/white to kill switch and stator.?


One pulse gen wire to trigger the other just open?


One pulse gen wire to trigger, other to somewhere within the rectification circuit within the CDI?


obviously I'll have to try every combo but if anyone could shed some light on the theory of the two wires from the pulse gen it would make understanding and solving the problem much easier or if anyone even has a photo of the wire arrangement in the quick connectors to the CDI I forgot to reference before I cut

Edited by sprucegooseduck

Wouldn't one wire of the pulsegen be 'signal and the other 'ground'?


If so they should be reversible to invert the signal.


Uploaded with ImageShack.us




Uploaded with ImageShack.us

Edited by Horri

Thanks a stack horri I should be able to pull apart the old board and reverse engineer using that.

that was my initial thought too Dave but no dice. If I ground the white/green wire the pulse gen doesn't pulse and acts like a mini stator. Ok brainwave the signal is AC right? Which would explain the two wires maybe positive goes up one and negative the other? Can you have a positive pulse without the pull of the negative?

We're straddling the line of bathroom philosophy and caveman electronics now...

I'll have to check whether the circuit from the pulsegen bypasses the diode array for rectification of the stator current (ac to dc)?

Edited by sprucegooseduck

I don't know ba about electrics..I have to ask though..Why didn't you just buy a CDI from Ebay..All this thinking about the project seems expensive compared to say $40.00.

Motorcycle courier been out of work for a month already. 400 bucks and a week wait for OEM here, ordered a hotshots unit from the states but 3 weeks is a long time to wait when ur homeless and about to run out of savings.

Motorcycle courier been out of work for a month already. 400 bucks and a week wait for OEM here, ordered a hotshots unit from the states but 3 weeks is a long time to wait when ur homeless and about to run out of savings.

Well that's no good mate..When you say you're homeless do you have a mailing address at all..I don't like seeing people buggering about on stuff if I can assist with a spare CDI??,,You want it it's yours,,pm me and I'll get it sent off in the morning..No charge.,Call it a rak.

What sort of plugs the old one,,same as the pictures above or is it a round plug.

The pulse generator is a variable reluctor sensor. It amounts to a piece of fine wire wrapped many times around a magnet and it generates an AC sine wave when a metal tooth passes by with the amplitude increasing with speed. There is no positive or negative per se; polarity is determined based on whether the system triggers on a rising or falling edge of the signal. It sounds like yours triggers on a rising edge. What you will probably end up doing is grounding one of the pulse gen leads and connecting the other one to the CDI.

Mate that's incredibly generous I really appreciate the offer but I've already got one on the way to a mate's place, just have to wait for the thing to show up!

I've built a theoretically functional CDI and wired it up the same as the OG with your help.

I've replaced the plug, the cap, lead, coil, stator checked everything with a multimeter I don't get it still won't spark.

You're right HT the green/yellow wire went to ground at the old CDI. Thanks for the concise info regarding how it works, I understand now.

Guess I'll go check my grounds again, again...

Does the green tab on the ignition coil go to the green wire on your bikes?

Edited by sprucegooseduck

Not a problem,,Hope things work out for you..I don't think it matters which wire goes to which side of the ignition coil..


Here's something I harvested from around the net sometime ago when I was wondering about the lead business..May be of some use,,may not..Dunno if both bits are about the same thing or not..Had it for a while..


You can take a lead (carbon) pencil and place the tip between the plug wire end cap and the plug (screwed into the head or just about any ground point) and kick it over. If the spark goes from the lead (end cap) to pencil point first, it's negative system and polarity is correct. If it goes from ground to pencil first, then it's positive gnd. Not right for a neg grnd system.It's a quick test to confirm or eliminate reversed coil polarity.

Place a wire from the coil about 1/4" from a grounded part of the
Insert the exposed lead from an ordinary lead pencil in the middle of the
(don't hold pencil in bare hand)
cause the coil to spark--A brighter reddish flash should emanate from one
side of the pencil lead---This should be the coil to sparkplug wire.  If
not, reverse primary leads.


Possibly useless info but what the heck,,Think I was concerned about whether the bike was a neg ground or positive system,,Who knows.,Electrical issues confuse the heck out of me..can't see it so have no idea what's going on with it..

Edited by Horri

hey that's a pretty cool trick I'll remember that.

headtrauma do you think my pulsegen is any good if it outputs max .1V AC and measures at 300ohms?

just a sine wave seems a little weak though and if that's not triggering the SDC thyristor to dump the caps into the coil that would explain a lot..

The factory pulse generator spec is 360-440Ω at 20°C, so 300 is a little on the low side. How are you measuring the AC voltage? 0.1V may only be an average depending on the meter used.

Some pulse generators will have the pulse start negative to positive, you can reverse this and make it go positive to negative by flipping the wires. If the pusle generator is internally grounded with only one output wire you obviously cant flip the wires as as the base mount for the pick up is the 'second wire". The attached pictures show what the typical signal looks like from the PG. You can see the difference in the direction it starts by flipping the wires. These were the best pics i could get using and Iphone it was pretty out of sync and wouldnt capture it well.


The other pic, not sure why they got rotated


Thanks heaps for uploading the waveform Ricky that's exactly what I was after.

I think I've got it pretty well sorted with the blue/white wire to trigger input via a diode rectification circuit and the green/white to grnd in the CDI same as the old CDI.

I've got a DMM which clocks the pulse from 005mv spikes at 100mv on AC setting at TDC.

I'm going to buy another PG I've got a feeling this one may have worn in with the old parts that were all a little tired, now with the new CDI it may not have the beans to trigger the switch in the CDI especially if the switch component is evaluating the pulse in comparison to the brand new high output stator... plus there's nothing else left to replace

Edited by sprucegooseduck

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