Hi, i am working on a pen wand scanner (MSH-119) project. The output of the scanner is TTL data. My question is: can we measure the TTL output using a multimeter? I tried it but the output is always 5v (because I connect a pull up resistor 5.1k between the power and the TTL output) no matter where I place the tip of the pen on.

Thanks

 

It is better to use an oscilloscope. That way you can measure the on and off times of the signals and actually see the bits. A multimeter can tell you if the output is beating up and down or it is fixed at a high or low level.

 

Yes, I used to do this regularly before I bought a scope for my second home. I still do it occasionally because its often more convenient than waiting for the scope to boot up.

If the logic signal is faster than the meter's response time (usually on the order of half a second, depending upon the particular meter) the voltage you measure will be the logic high voltage times the duty cycle. In your present case, this applies if the pullup resistor has a low enough resistance for the signal to faithfully switch while driving the capacitance of the meter leads and meter input.