I think the spec sheet states + 0.5 volt

The 4077 needs a signal voltage between its supply voltage and ground.
If your signal is only ±0.5V then you can translate it to the proper level with a comparator such as the LM339/393.

 

Frequency doubler - low frequency- square wave

I am using a hall effect device to measure the speed of an enclosed shaft.
The output is fed to a cheap pulse counter that can be configured to display pulses per sec or pulses per min.

The speed of the shaft varies. The normal range is from 5 rotations per sec to a max of 250 rotations per sec.

The problem is that the pulse counter is neither stable or accurate below 10 pulses per second.

The easiest solution is to the double the input frequency.
The counter has x1 , x2 and x10 multiplier for the display.

The doubled the input frequency is easily corrected at the display.

I am hoping some one can direct me to a circuit that can perform the frequency doubling function I require.

Thank you

do what WBahn said - or there's a few electronic methods, one of them uses an XOR gate but I don't remember the details.

 

Here's the LTspice simulation of an example circuit using XNORs.

View attachment 148124

I am trying to digest this circuit.
Is this correct?

 

Hi Les

Something like this?

This is not what he described (cap to ground) and neither work in simulator.

 

Is this correct?

Yes, except for power to pin 14.

 

Should the signal voltage from the HE sensor be limited before feeding the signal to the 4077.
I think the spec sheet states + 0.5 volt

Not limited, amplified.
The circuit needs a signal voltage equal to the supply voltage.
For + 0.5 volt signal you need to add a comparator as I suggested in post #21 to boost the signal.