DC-to-1MHz F-to-V

dark · Oct 3, 2009

Hi,

I require to convert DC-to-1MHz to voltage scale , is there any dedicated IC for this . I can see an LM331/LM2917 F-to-V could measure upto 10KHz (cant see any reference).
TC9400 doesnt have an industrial temperature range though it can measure upto 1MHz . How to go about with such a conversion .

Thanks

Ubergeek63 · Oct 3, 2009

dark said:
I require to convert DC-to-1MHz to voltage scale , is there any dedicated IC for this . I can see an LM331/LM2917 F-to-V could measure upto 10KHz .
TC9400 doesnt have an industrial temperature range though it can measure upto 1MHz . How to go about with such a conversion

I do not think there is an analog IC capable of over three decades of frequency linearly. Your statement says DC as opposed to what you actually need.
Wanting an analog part implies an analog output, which means you will be limited by the resolution of your meter.

Most digital meters are only 3 or 4 digits meaning you would have to scale it since 0.1MHz (100KHz) to 1MHz is 4 digits, but then you have individual scale calibrations and accuracies (you also do not mention how much accuracy you need).

I do not normally recommend micros, contrary to the trend here, for functions of this simplicity, but in this case you are much better off doing a period measurement in a micro timer and inverting it in software. Then, if you insist on have an inaccurate analog level, you can send it to a D/A.

Dan

ericgibbs · Oct 3, 2009

dark said:
Hi,

I require to convert DC-to-1MHz to voltage scale , is there any dedicated IC for this . I can see an LM331/LM2917 F-to-V could measure upto 10KHz (cant see any reference).
TC9400 doesnt have an industrial temperature range though it can measure upto 1MHz . How to go about with such a conversion .

Thanks

Hi,
Are you sure about the 1MHz for the TC9400.???

dark · Oct 3, 2009

ericgibbs said:
Hi,
Are you sure about the 1MHz for the TC9400.???

O sorry , Please omit that I wanted to mention some other Commertial grade part , which I couldnt locate at the moment .

Regards

dark · Oct 3, 2009

Hi ,
Should I use two stage 74HCT191 2^4 divide stage and 2^3 to lower the frequency by roughly 7Khz ? . Is this a good idea to do without sacrificing any linearity ? . I am afraid what happens when a 5Hz signal gets divided this way I am left with 0.04Hz ? . Will this be benificial to do against LM2917 .

Regards

ericgibbs · Oct 3, 2009

dark said:
Hi ,
Should I use two stage 74HCT191 2^4 divide stage and 2^3 to lower the frequency by roughly 7Khz ? . Is this a good idea to do without sacrificing any linearity ? . I am afraid what happens when a 5Hz signal gets divided this way I am left with 0.04Hz ? . Will this be benificial to do against LM2917 .

Regards

hi,
Is the frequency source varying over the full 10Hz thru 1MHz.?

You could use a 74LS93, divide by 5, then by 2 in order to give a 50/50 mark space, before the F2V ic.

Warpspeed · Oct 3, 2009

I think you need to be a bit more realistic about the lower frequency limit.

Suppose you had .001 Hz incoming, would you be prepared to wait over a quarter of an hour for the output voltage to update ?

bountyhunter · Oct 3, 2009

I recall the F-V converter in the funtion generator I built was good for about 10Hz to 200 kHz. I believe the IC I used was the Exar XR-4151 or similar.

http://www.datasheetcatalog.org/datasheets/1150/285098_DS.pdf

dark · Oct 4, 2009

ericgibbs said:
hi,
Is the frequency source varying over the full 10Hz thru 1MHz.?

You could use a 74LS93, divide by 5, then by 2 in order to give a 50/50 mark space, before the F2V ic.

Hi,
yes its the signal from a sensor which outputs a linear range of frequency from 0.005KHz to 900KHz for equivalent light levels. As said to use two dividers first divide by 5 and then by 2 . Is it necessary to keep the lowest division to 1Hz? .

Thanks

dark · Oct 4, 2009

Warpspeed said:
I think you need to be a bit more realistic about the lower frequency limit.

Suppose you had .001 Hz incoming, would you be prepared to wait over a quarter of an hour for the output voltage to update ?

Hi,
Yep you are right .1Hz should be the lowest level to not keep waiting toooooo long .

bountyhunter said:
I recall the F-V converter in the funtion generator I built was good for about 10Hz to 200 kHz. I believe the IC I used was the Exar XR-4151 or similar.

http://www.datasheetcatalog.org/datasheets/1150/285098_DS.pdf

Thanks for the part I will check the datasheet , but it looks like similar to LM2971 .

ericgibbs · Oct 4, 2009

dark said:
Hi,
yes its the signal from a sensor which outputs a linear range of frequency from 0.005KHz to 900KHz for equivalent light levels. As said to use two dividers first divide by 5 and then by 2 . Is it necessary to keep the lowest division to 1Hz? .

Thanks

hi,
If its possible, I would only switch in the div by 10 for frequencies over 100K.

Warpspeed · Oct 4, 2009

The way to do this is to trigger a 1 microsecond monostable with your incoming frequency.
You then feed the output through a very sharp low pass filter that cuts off above 5Hz.

The output will then be a dc voltage proportional to frequency that responds fairly quickly, even at 5 Hz.

That is really all an f/v chip does anyway, but you will need to build your own filter even if you do use a commercial f/v chip.

Dean Huster · Oct 4, 2009

You could use a 74LS93, divide by 5, then by 2 in order to give a 50/50 mark space, before the F2V ic.

The 74LS93 is a ÷2/÷8 binary divider for a ÷16. It would have to be a 74LS90 to get the ÷5 and ÷2 you need.

ericgibbs · Oct 5, 2009

Dean Huster said:
The 74LS93 is a ÷2/÷8 binary divider for a ÷16. It would have to be a 74LS90 to get the ÷5 and ÷2 you need.

hi Dean,
You are correct, careless of me, thanks for the catch.

Ubergeek63 · Oct 5, 2009

oy, as i said-the catch is the range. with out a range switch you lose one end or the other.

Warpspeed · Oct 5, 2009

Range is NOT the problem.

The problem is converting a 5Hz signal to dc (with minimal 5Hz ripple) that does not take all day to settle.

DC-to-1MHz F-to-V

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