I'm pulling a signal from my motorcycle tachometer circuit. it seems to be a 50% duty cycle square wave at battery voltage.
I needed to bring it down to 5v and, not wanting to interfere with the ignition i used 1M & 470K resistors. It works great but I find i get occasional spurious pulses, maybe once in 20 revolutions.
They currently get filtered out by the software but I wondered if they might be a result of using too high a resistance in the interface - there's presumably lots of EMF floating around the coils and maybe the 1M resistor lets it show up as detectable voltage.
I'm re-doing the circuit so I thought I would ask for advice - go down to 100K/47K? lower? put in a small cap on the microprocessor side of the divider?
I needed to bring it down to 5v and, not wanting to interfere with the ignition i used 1M & 470K resistors. It works great but I find i get occasional spurious pulses, maybe once in 20 revolutions.
They currently get filtered out by the software but I wondered if they might be a result of using too high a resistance in the interface - there's presumably lots of EMF floating around the coils and maybe the 1M resistor lets it show up as detectable voltage.
I'm re-doing the circuit so I thought I would ask for advice - go down to 100K/47K? lower? put in a small cap on the microprocessor side of the divider?