Re: Opto Isolator board single sided
Posted: Tue Aug 04, 2020 9:00 pm
What is that zener diode going to do?
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The raw ignition signal is passed through a diode to prevent negative voltage transients.
Then the signal is clipped via a Zener diode so voltages lower than 75v 110v are discarded. This filters out the ringing components of the signal, which is the primary cause of false triggers.
The clipped signal is passed through an optoisolator via current limiting resistors.
The optoisolator output is further filtered through a single inverting logic gate using a schmitt trigger filter.
The John Zener(5.1V) is used for some specific ignition systems which do not pull the load all the way to ground potential - the application of this diode depends on installation (it is recommended to install a jumper in place of the John Zener for first ignition tests - if noise or lack of triggering is present then the diode should be installed).source: http://www.bgsoflex.com/v22/msv22.html , Hope that helps clear that up.
zylinx wrote: ↑Thu Aug 06, 2020 5:38 pm… First I noticed the 5.1V Zener diode come into question from a MS circuit, I noticed this in one of my open tabs:It does for the original intent of certain problematic installations (force opto to ground and shut off). It does not for additional considerations not taken into account in the pieced-together MS circuit, which is what romP44 is addressing. See below.The John Zener(5.1V) is used for some specific ignition systems which do not pull the load all the way to ground potential - the application of this diode depends on installation (it is recommended to install a jumper in place of the John Zener for first ignition tests - if noise or lack of triggering is present then the diode should be installed).source: http://www.bgsoflex.com/v22/msv22.html , Hope that helps clear that up.
zylinx wrote: ↑Thu Aug 06, 2020 5:38 pmI was wondering If the 4N35 and 4N25 interchangeable between NickZ's nad dazq circuits ? or is there something im missing in the datasheets.They are very similar, but have a few different characteristics, especially in voltage isolation, maximum LED current, and substantially different transfer ratio. While they can be interchangeable in some cases, the differences may need some attention for proper operation. For examples, in romP44's circuit, they should work equally well, but in NickZ's the 35 could have some advantage. One difference would be in the tighter minimum saturation limits against the lack of the Zener in Nick's.
zylinx wrote: ↑Thu Aug 06, 2020 5:38 pmAlso would it be ok to use a 100V Zener instead of 110V ?Maybe. That depends on the coil's output waveform and the ringing voltage after spark burn. The point in improving the circuit would be to "cut-out" secondary triggers, only using the initial HV spike while ignoring all others.
zylinx wrote: ↑Thu Aug 06, 2020 5:38 pmI tried to make NickZ's circuit but LED2 keeps blowing when I test by putting 19V DC across coil input. I thought it would be able to withstand 19V easily but the 2.2K resistor gets warm and LED is very bright then dies, not sure if I also damaged the opto-isolator aswell. Am I being stupid ? Should this circuit be able to handle 19V on its input ? I would think so. I must have made an error somewhere.....Yes, we are back to using only the HV spike, by using the HV zener, to do a few things. One is to greatly limit the on-time of the opto LED (or any indicator LED) to only that short discharge, which limits the average power through the LED and therefore limits the possibility of burn-out. No big deal, as that can be compensated with resistor values. However, the HV Zener moves the timing of the trigger signal to the actual coil firing point.
Sunglasses wrote: If the RPM LED lights up, the IR LED in the optocoupler will do as well since its forward voltage is lower compared to LEDs emitting visible light.Yeah the LED does not provide lots of info but I just wanted to make sure I was picking up some strobing at idle.
romP44 wrote:Quick test with my Arduino and a LED:Great! Thanks for doing the test, it correlates with what I saw in practice. very fast strobing at idle, solid when I rev.
Any frequency higher than about 40Hz is not visible anymore (pulse duration 1ms). That's 1200 RPM with 4 cylinders (2 sparks per revolution).
So the LED would be useful only at idle.
romP44 wrote: ↑Fri Aug 07, 2020 8:00 am Quick test with my Arduino and a LED:I have diagnostic LEDs on my board designs, and they are surprisingly useful at higher speeds or tooth-counts. While you can't see individual flashes except at cranking and perhaps idle (even a 60-2 wheel is a blur at cranking), the eye can notice skipped or long pulses and other anomalies. Note the diag LEDs on boards such as the MiniMAX-A2 and DSC are on the output side, so indications are not of input signal activity, but conditioner output results (what Speeduino should see).
Any frequency higher than about 40Hz is not visible anymore (pulse duration 1ms). That's 1200 RPM with 4 cylinders (2 sparks per revolution).
So the LED would be useful only at idle.