LED Timing Light circuit.

[Biggles]

Hopefully this subject isn't too automobile orientated for the forum but here goes. I am in need of an old style timing light to check and adjust ignition timing on my motorbike. My original xenon gun is unreliable to say the least so I had planned on using the HT lead to trigger a 555 timer chip configured as a monostable with a very short time constant, too short to affect timing accuracy, and use the output to drive maybe four high intensity white LEDS. The "flash" from the LEDs hopefully being bright enough to illuminate the timing marks on the flywheel. If anyone has any suggestions or previous experience with circuits for this I would be interested to hear about them so I don't waste hours tinkering with a circuit which will be used once a year at most. I did think about using an LED torch as the "gun" part of the unit.
Alan.

[philthespark]

You can pick a new timing light up for less than 20 quid on eBay, I'd just do that.

[Bazz4CQJ]

have you had a look on the "instructables" website https://www.instructables.com/ - sort of thing that might appear there.

B

[julie_m]

How about wiring the LED (with a suitable series resistor) the wrong way around across the primary side of the coil, so it lights from the back EMF when the contact breaker opens?

[Oldcodger]

Alan, many years ago, I had similar problems with an old Marina. My previous timing light was based on an old CV COLD CATHODE tube, which needed a lot of insulation as one pin was connected to the HT, and any failure in insulation meant spark problems and HT BELTS.
So I researched XENON tubes, and found one ( sold at the time by Tandy), which needed 250 volts to strike, and I used a pulse transformer to derive a lower voltage strike voltage. Then I found tht the leakage from the HT LEADS was sufficient.
250 HT was derived from a TL494 , driving a very inefficient transformer, with a 2 uF smoothing cap after rectification. Again a modification of a GEC 494 circuit.
Some posters on here have suggested I modify the circuit to accommodate a transformer from an old switch mode laptop supply.
So -something to look at, and experiment with.
But ,another idea- a lot of headlamp bulbs these days are XENON, AS 12V. Make a 494 circuit to convert 12v- 12v ,and add a trigger ,operated from vehicle HT and Robert is the husband of brother's sister.

[Biggles]

Thanks for the suggestions. The real drive behind using LEDs was to hopefully get round the xenon tube intermittent flicker i.e. not triggering on every spark. This is annoying to the extreme and a reliable trigger system is the crux of the new design. I am reluctant to buy a new xenon type in case it has the same problem as my old one. The bike ignition is pretty much the same as any car one as it runs from 12 volts and has an electronic conversion which I have just fitted and hence the requirement to set the timing. Although the original light is intended for cars it has performed well in the past for bike ignition but as it is thirty years plus in age it's probably past it's best.
Alan.

[Terry_VK5TM]

About as simple as you can get (without being over simple):

https://www.eeweb.com/extreme-circui...d-timing-light

[Argus25]

Actually, almost as simple as you can get. It is easy to avoid having to make the inductive pickup with its core and winding. Its easier just to wrap a few turns of wire around the spark plug lead insulation and it forms a gimmick capacitor. Then it's fed via a high value resistor, and clipping diodes & resistor to the gate of a Hex inverter IC and then it can go on to trigger a 555 timer to extend the pulse width a little, or just to pulse the LED driver directly.

[Biggles]

I might try that circuit. It has a few more LEDs than I had envisaged but someone else has probably done a little bit of experimental work which will save me the bother. I have all the bits apart from the LEDs although I have lots of blue very high intensity LEDs salvaged from beacon lights from emergency vehicles in a previous job which may do at a push. (They used to suffer damage regularly by vehicles driving under roofs with very little clearance, along with the radio aerials and all!)
Alan.

[philthespark]

You haven't got any of the red high intensity modules have you, I could do with a couple for my motor. lol

[Biggles]

Unfortunately not. It was all blue lights and grill strobes when I left the service ten years plus ago. The old rotating beacons sometimes melted if the motor failed. The LED ones were pretty bright if you were close to them. We also had some light bars for roof fitting which would mysteriously switch on even when no one was in the vehicle. We traced this to floating logic without pull down resistors so the control logic used to give false highs. What with RF floating about this gave rise to all sorts of problems. A quick resistor mod soon calmed it down. I think the original design used illuminated switches which naturally pulled down to earth via the internal lamp when "off".
Alan.

[G6Tanuki]

Remember that if you're pulsing the LEDs with a short duty-cycle you can significantly exceed the maximum continuous-current limit in the interests of greater brightness.

[Biggles]

The pulse will have to be of short duration to ensure timing accuracy so it should in theory be possible to stay within the device dissipation limits, even with a relatively high transient current. I will have to check absolute Imax for the LED's though. I think with high intensity devices the actual brightness will be adequate because of the nature of the aperture the timing marks are inside. The marks are inside a small hole which makes it awkward to use a normal size timing light. This is why I think a relatively small but intense light would work quite well.
Alan.

[Biggles]

Just a quick update on this one. Earlier today I bought an LED torch at the local pound shop and dismantled it. Using the focused five LED array I built a driver circuit using a 555 timer in mono-stable mode with a BFX85 power transistor switching the LEDs. The time duration is calculated to have minimal effect on timing accuracy and the trigger input on the 555 is used as a proximity pickup from the HT leads. It works fine and the small focused beam from the torch is ideal to direct through the crankcase aperture. All in all it cost me a couple of quid. Result!
Alan.

[julie_m]

Absolutely!

Pound stores can be a great source of stuff that can be repurposed, and even the cost of a failed experiment is minimal. You can even get a USB power bank (only 1200mAh, but better than a poke in the eye and comes with a 15cm. USB lead) and a plug-in charger for £1 a time, and then you need to add in a USB lead that you can cut the "appliance" end off and use the "computer" end to plug your finished project into either one.

[Biggles]

Well worth a browse round the local pound shop. You can't go wrong at five hi intensity leds and a 4 AAA battery holder and a nice hand held project case to house the electronics in all for a pound. The only thing with the torch is that there is a little embedded chip for the flash function (I was hoping it didn't have the flash on it but the Spanish? instructions on the packaging didn't say either way). The chip was easily isolated from the leds by cutting a track on the PCB. The leds were all in parallel so a quick measure of current on the original torch gave the design conditions for me to work to. A small confusing hiccup occurred while actually setting the timing. The bright sunlight upset the opto pickup on the electronic ignition. Wasted a good half an hour wondering why I had an intermittent misfire until I twigged and put the cover back on. A lesson learned for next time. All in all an interesting little project.
Alan.