Building a strobe timing light with a rotation angle delay, without a microcontr - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: May 02, 2023, 05:14:02 am
content: Is there a circuit that can delay a pulse, where the delay length is actually a result of the pulse frequency and the input setting?So if there's a pulse every 1ms, and the setting that's input is 10 degrees, the output pulse should be: (0.001s / (360 / angleInput)) = 0.28mS after the input pulse.So the output pulse is delayed based on the angle of rotation instead of just a static time delay.Oh and 1ms is just an easy-math example, the actual range would be around 120ms - 12ms (1000 to 10000rpm, and double that time because trigger pulse will happen every 720 degrees of rotation)

author: Ian.M
author_rank: Super Contributor
timestamp: May 02, 2023, 06:21:40 am
content: Its certainly possible, as all the building blocks required to brute force a solution are reasonably well known. e.g. F=>V, some analog computing to get 1/x and a voltage controlled delay line. If the aim is to generate a trigger pulse with angular offset, it can be simplified with a voltage controlled monostable delay instead of a delay line. Some additional analog computing will probably be needed to linearize the F=>V output voltage and the dela or monostable control voltage response. However I wouldn't expect either solution to be stable enough open loop.An alternative approach which is more promising from a stability viewpoint might be a sine cosine oscillator, voltage controlled via a pair of analog multipliers, PLLed to the input pulse. Any desired phase angle output can be generated by summing sine and cosine components (inverting as required), and then a comparator can trigger a monostable on rising zero crossings to give the desired output pulse. Angular stability would depend on how good the PLL is, and how accurately the sine and cosine amplitudes match, and how exact the 90 deg phase shift between them is, over the operating frequency range.However no one in their right minds would do it that way vs using a cheap MCU with input capture and output compare, and enough MIPS to calculate a proportion of the period on the fly to update the compare delay.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 02, 2023, 09:36:33 am
content: Quote from: ELS122 on May 02, 2023, 06:49:41 amI find that confusing. Could you post something similar to a timing diagram showing what your want to do? A delay is simply an inverted pulse, right?

author: darkspr1te
author_rank: Frequent Contributor
timestamp: May 02, 2023, 01:57:47 pm
content: maybe this will helphe makes his own timing light for a car.darkspr1te

author: Ian.M
author_rank: Super Contributor
timestamp: May 02, 2023, 03:40:39 pm
content: A modification to the ramp generator based approach would be to use a F=>V circuit to make the charging current proportional to the pulse rate so the ramp is the same amplitude over the operating RPM range.

author: langwadt
author_rank: Super Contributor
timestamp: May 02, 2023, 03:41:57 pm
content: not doing it with a mcu would make Rube Goldberg proud ...

author: jpanhalt
author_rank: Super Contributor
timestamp: May 03, 2023, 09:03:21 am
content: Measuring current might be easier than you imagine. Here are two links I used to make a current probe for my oscilloscope.Deeker Inductor test benchhttps://www.dos4ever.com/flyback/flyback.html#ind2Linear Technology (now Analog) current sense methods:https://www.analog.com/en/app-notes/an-105fa.htmlMy method was simply a small ferrite toroid core was several wraps of wire. The pictures pretty much explain it. I found it easier to cut a side off the ferrite core for a nice fit rather than cut a gap.

author: CaptDon
author_rank: Super Contributor
timestamp: May 03, 2023, 12:51:29 pm
content: Current probe pickup is absolutely the way to go. You can have spark voltage but no spark current with fouling and so forth. When you detect current there is a 99% chance that will be the instant the spark broke over and ignition began to occur!! The current approach is more accurate. Many of the current probe timing lights used a 'sensitive gate SCR' to fire the Xenon strobe. With today's ultra bright white LED's a Xenon strobe is history. With a current clamp timing light you can even use it on an EFI diesel engine as an added bonus. Up until my recent retirement I was designing engine control packages for GE/WABTEC locomotive engines, 7FDL, GEVO, Advantage Edge upgrade and others. I have built several 'homebrewed' timing lights for specific applications. My most rewarding experience with engine timing came from having unlimited access to an old SUN distributor testing machine!! The pruning and tuning led to about a 1/2 second quicker 1/4 mile time for an old Plymouth I owned.