scmitt trigger and 0-gate

[johnsold]

Yes, yes, and yes.

The frequency is not a problem. The opto coupler is likely to be much slower than the comparator. It is probably limited to a few kilohertz or tens of kHz, while the comparator will probably go to about 1 MHz.

If it works, I would not worry about improvements. The things that might become issues are the magnitude of the on-state current of the photo-transistor. Depending on stray light, reflectivity of the target, and the sensitivity of the device, the threshhold of the comparator might need some adjustment. If this is a one-of-a-kind test, just adjust the resistors to get it to work.

Everything there will work fine from the DAQ 5 V. Slight adjustments may be needed.

Lynn

[labview1958]

I found there is a problem. I am using LM319. It has a rise time of 80 ns. LabVIEW counter can only detect squarw wave with a rise time of less than 50 ns. Really stuck. How to improve LM319?

[johnsold]

Someone on the other thread suggested adding a 74HC14 between the comparator and the counter input. It has a rise time of around 20 ns with a 5 V power supply. Use two sections if you do not want the inversion. Also, any unused inputs should be grounded (applies to the LM319 also).

Lynn

[labview1958]

How to connect the output of LM319(high speed dual comparator)  to the input of 74F14 (Hex inverter schmitt trigger)? It looks to me 74F14 has six inputs and six outputs while I am using only one output from my LM319. Can I choose any one of the six?

[Ryan_V[DE]]

If you were ever applying 6V to the inputs of your 6025, I would worry about damage to the board. Do you know this counter input to be functional? I would try generating a pulse train on counter 1 and measuring it on counter 0. Even though your rise time is above the maximum specified for the device, I would expect some periods to be measured. What is the behavior you are seeing in your application? Are you ever getting any period measurements returned? Is the operation timing out?

Hope this helps,

[AnalogKid2DigitalMan]

"How to connect the output of LM319(high speed dual comparator)  to the input of 74F14 (Hex inverter schmitt trigger)? It looks to me 74F14 has six inputs and six outputs while I am using only one output from my LM319. Can I choose any one of the six? "

Use one gate as follows, suggest you power your entire circuit from the +5 out on the DAQ:

Output from 319 circuitry goes to Pin 1

Pin 2 goes to DAQ Counter input

Pin 7 goes to DGND

Pin 14 goes to +5 out on the DAQ.

Pins 3,5,8,11,13 (unused inputs of the remaining 5 gates) all go to +5 to provide best noise immunity and switching speed.

[majeed]

I understand labview1958 circuitry. I have gone that way. The measure period would give a wide range of readings. However only the lower quarter of those readings are reasonable. So the best is find the average of those 25% of the lower readings. So far I have used min. & max. vi to find the lowest minimum reading.What I need is the averag of those lower readings. Another thing the measure period.vi likes to hang. How to time it out or proceed without measuring or ignore. It sometimes fail to measure the period and hang. Furthermore it would hang the entire program.