measuring time interval signals using a watch

[walters]

I did a couple of things at work today that i don't understand


1.) I had to measure a signal from the microcontroller
To measure this signal , First i had to put a 1ohm resistor into the batterys and to the PCB and measure the voltage using the oscilloscope and Fluke meter which was across the 1 ohm resistor . The tech wanted me to use the oscilloscope in normal trigger mode to see the microscontrollers signal flashing at a interval rate.

It was just an DC voltage flashing at a time interval, but what is confusing for me is this
1.) The oscilloscope or multimeter wasn't fluctuating or pulsing using the 1 ohm resistor. It only worked when you put a 10ohm or 15ohm resistor not the 1ohm resistor, why is that?

2.) Once We got the oscilloscope and DVM meter to see the DC fluctuating and pulsing , the tech wanted me to count how many times in a minute did it pulse at. It was 30 pulses in a minute. The tech did some match by taking 30 pulses and 1 minute of time and used a formula to convert that into a time interval but i don't know how, do u guys know?

 

[ZekeR]

1.) The oscilloscope or multimeter wasn't fluctuating or pulsing using the 1 ohm resistor. It only worked when you put a 10ohm or 15ohm resistor not the 1ohm resistor, why is that?

With the 1 ohm resistor, it did indeed pulse; however, it was 10 to 15 times smaller, so you were less likely to see it. The pulses you saw on the oscilloscope were voltage pulses. Voltage pulses of 10 millivolts across a 1 Ohm resistor means Current pulses of 10 milliamps (Ohm's law, V = IR). Using a 10 Ohm resistor, voltage pulses of 10 millivolts would correspond to current pulses of only 1 milliamp. You were measuring some small currents.

2.) Once We got the oscilloscope and DVM meter to see the DC fluctuating and pulsing , the tech wanted me to count how many times in a minute did it pulse at. It was 30 pulses in a minute. The tech did some match by taking 30 pulses and 1 minute of time and used a formula to convert that into a time interval but i don't know how, do u guys know?

If it pulses 30 times in a minute, then that is 30 pulses in 60 seconds. 30pulses/60seconds = 0.5 Hz (that's the frequency, in standard units of Hertz). Alternately, the time interval between each pulse is 60seconds/30pulses = 2 seconds per pulse (that's the period).