Help me to digital read low volt( about 1.1-1.3v) pulse as HIGH

I using arduino to count RPM for my bike,I read digital pulse by winding wire around spark plugs’s wire but it was 1.1-1.3volt with GND at my bike , that Arduino can’t digital read ít. Please help me.

spark plugs's wire but it was 1.1-1.3volt with GND at my bike

A motorcycle? Of course, the actual spark is thousands of volts...

that Arduino can't digital read ít. Please help me.

Right. Anything less than 1.5V (0.3Vcc) is logic low. Anything greater than 3V (0.6Vcc) is logic high. in-between is undefined.

However you can connect to an analog input. You can set a threshold wherever you want. 1V will read 205 on the 10-bit ADC. So your logic would be, if ADC reads greater than 200 do one thing, otherwise do something else.

BTW - How are you reading that voltage? A multimeter won't read a pulse accurately... Assuming you're not actually reading the spark voltage, I'd expect 12V or 5V. (And more than 5V can damage the Arduino.)

DVDdoug:
How are you reading that voltage? A multimeter won't read a pulse accurately... Assuming you're not actually reading the spark voltage, I'd expect 12V or 5V. (And more than 5V can damage the Arduino.)

yoboto:
by winding wire around spark plugs's wire


I am using there, the yellow wire is pulse to arduino, the black wire is the spark plug wire.

Please don’t connect the yellow wire direct to an Arduino input, it will consist of a negitave and positive pulse greater than 5V. When I tried this in the late 60s I got enough voltage to light up a neon. That is in excess of 70V.

You need to use a diode to remove the negitave pulse and then a pull down resistor and then a seriese resistor to the input. Then you need a diode from the input as well to the 5V supply.
Only then can you hope to read the pulses without damaging anything.

Grumpy_Mike:
Please don’t connect the yellow wire direct to an Arduino input, it will consist of a negitave and positive pulse greater than 5V. When I tried this in the late 60s I got enough voltage to light up a neon. That is in excess of 70V.

You need to use a diode to remove the negitave pulse and then a pull down resistor and then a seriese resistor to the input. Then you need a diode from the input as well to the 5V supply.
Only then can you hope to read the pulses without damaging anything.

oh, I had used diode to trans AC to DC pulse, but my problem is the pulse less than 3.3v for the arduino digital read.

yoboto:
oh, I had used diode to trans AC to DC pulse, but my problem is the pulse less than 3.3v for the Arduino digital read.

Well, if your photo is to be believed, it is a highly unreliable arrangement.

Noting the requirement as Mike points out, for a diode to both ground and Vcc, you need to tape perhaps an inch or so of your wire alongside the plug lead so that it is consistently in contact.

For your actual implementation, you would hold the two insulated wires together with an inch or so of heatshrink through which you had threaded them.

I had used diode to trans AC to DC pulse

So kind of you to tell us that before you lead us astray, now what about the pull down resistor?

but my problem is the pulse less than 3.3v for the arduino digital read.

Then use a transistor to get it up to the rail.