Arm Mbed OS support forum

A question about LM555

Hi, dear all.
My question seems to be a little complicated. I am so sorry about that :dizzy_face:
I have a question: I am designing my own capacitor discharge ignition system for a classic 1970 Honda. I think the LM 555 in monostable can give me a 3ms pulse output when the breaker points open (with a few simple mods). But the trigger voltage will last longer than 3ms (it’s like holding down the trigger button on your board). So can I get that short pulse no matter how long the trigger signal is applied? Then reset after the trigger signal is removed.
My intention is to use MOSFET to fire off a charged capacitor (200-300v from a cheap Chinese eBay booster circuit) across the ignition coil primary every time the breaker points open (for 3ms) then after that the capacitor is charged again as MOSFET goes open circuit. Another MOSFET will briefly cut the HV supply as the capacitor shorts across the (0.4 ohms) coil primary to avoid damaging the booster circuit.
Thanks for listening!


It seems to be like an advertisement of an e-shop, so how is it related to the Arm Mbed?

all other thread of this nature will be marked as spam. Same situation for the new topic from today morning. If you want to discuss about a component then share manufacturer datasheet not eshop page, but your goal is probably different one.

BR, Jan

I think Jan is right! But in case someone is considering to use a 555 timer for such function

The short answer is, No. In such case the pulse will last until the button is released. (To advertise Mbed :slight_smile: ) It’s better to use an ARM chip. The Timeout seems to be a suitable API for that.