M
Miles
- Jan 1, 1970
- 0
Hello,
I built a circuit for a motorcycle which cuts off power to the
ignition coils for several milliseconds when a switch is pressed to
fire an air shifter. It works well, but sometimes it triggers for no
reason (ie. switch was not pressed).
The circuit is powered by a LM2937 automotive regulator. The timming
is done with a 555 in one-shot mode. I think the problem is lack of
filtering on the trigger wire. The trigger wire will be switched from
an open, to 12V.
Any ideas on a really solid noise immune way of converting that noisy
12V line to a 5V logic level for the 555? My revised idea is to use
the following signal path:
1. 12V unregulated
2. 20V TVS
3. LC low pass filter
3. Voltage divider (Divide signal by 4)
4. Pull Down resistor
5. 5.1V Zener
6. Schmitt Trigger output to 555 timer trigger pin
Do you think this will work? What values for my low pass filter
should I be looking at?
Thanks for your help.
I built a circuit for a motorcycle which cuts off power to the
ignition coils for several milliseconds when a switch is pressed to
fire an air shifter. It works well, but sometimes it triggers for no
reason (ie. switch was not pressed).
The circuit is powered by a LM2937 automotive regulator. The timming
is done with a 555 in one-shot mode. I think the problem is lack of
filtering on the trigger wire. The trigger wire will be switched from
an open, to 12V.
Any ideas on a really solid noise immune way of converting that noisy
12V line to a 5V logic level for the 555? My revised idea is to use
the following signal path:
1. 12V unregulated
2. 20V TVS
3. LC low pass filter
3. Voltage divider (Divide signal by 4)
4. Pull Down resistor
5. 5.1V Zener
6. Schmitt Trigger output to 555 timer trigger pin
Do you think this will work? What values for my low pass filter
should I be looking at?
Thanks for your help.