Hello.
We have a variable reluctance sensor that we would like to buffer to a TTL or other voltage level. The LM2907/2917 seems like a good candidate. On page 20 of the datasheet, figure 28 a circuit is described that outputs pulses at twice the frequency of the input frequency.
I assume the unit of the duty cycle is time and as our Vcc is 24V the duty cycle will equal C1 according to the formula. We will sample the pulse train with a minimum frequency of 9 MHZ and a maximum of 30 MHz.
Assuming we sample the pulse train with 9 MHz we have to have a pulse width that is wide enough that the sampling device will detect it.
For example lets say the waveform has a frequency of 4.5 MHz and the duty cycle is 50%. I want my two-shot output duty cycle to be of the same time duration. Assuming Vcc = 24 that leaves me with a C1 of 11 uF. Is there any danger in using this large a capacitor?
In the example the capacitor is 500 pF which is way less and I reckon this would be used with an MCU to calculate the frequency using some interrupt service routine triggered by the pulses. We want to sample the waveform and do calculations afterwards.
The DAQ used is the NI 9401. The reason we want to use this and sample the waveform is to integrate it with other NI modules with which we sample other signal types.
Any suggestions/ideas?
Best regards,
David Kantzon
