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I have a rotary encoder which sends out 1000 TTL pulses for every one rotation. I need to be able to capture the analog voltage output signals, convert them to digital with my PC, and then produce a running real-time graph of the pulse frequency vs. time. I'm looking for hardware and software products that will work? I only need 2 channels and the sampling frequency does not have to be high. I just need to be able to display the captured waveform and then quantify it in real time. I've found digital oscilloscope programs that use the sound card input, but problems there include lack of DC coupling (so the pulses are highly attenuated and register in AC only) and the programs have no means of quantifying pulse count in real time.

Thank you for your questions. You may consider our USB DSO products (https://www.virtins.com/oscilloscopes.shtml) such as VT DSO-2820, VT DSO-2810, etc. By default, these USB DSOs come with a hardware activated Multi-Instrument Standard license. The Multimeter function of Multi-Instrument can be used to display the pulse rate in Hz. You can also switch the display to show RPM instead after entering the number of pulses per rotation.

If you want to display pulse rate vs time or RPM vs time, you need the Multi-Instrument Add-on software module: Data Logger (US$99.95).

It may be possible to use a sound card to do the measurement, despite the fact that the captured waveform may be distorted due to its AC coupled input. As long as the sampling rate of the sound card is sufficient to resolve the pulse rate, Multi-Instrument should be able to display the correct pulse rate / RPM.