Frequency divider

GopherT

Joined Nov 23, 2012
8,009
View attachment 96826

Here is partial schematic.
I'm triggering 555 from output of hall sensor. Then processing it and routing back to input of controller.
There isn't access to see what the hall circuit consists of, or the nature of controller input.
I do know that the hall pulls 9v input down to near zero.10k pulls the same input to 1/2. Giving an idea of the input impedance.

This circuit works fine when inserted in line between original hall sensor and controller. Logic after 555 not shown. That part works fine.

The problem I have is, connecting anything additional to hall effect output, stops the 555 from triggering.
There is a tachometer that needs to be connected to hall for setup.

R3 pull up is needed. I don't understand why, as hall out put makes full swing either way.

Tach has high impedance input. Even added a 47k right at hall output to keep from loading it. If I even connect 10' of 2C wire, the 555 following connection fails to trigger.

Tach is self powered and isolated. 9v battery

This circuit has a few issues...

Remove R3 (the resistor on the hall sensor is the only connection you need to the cap.

Change R1 to 1M. 10k is swamping out the signal from the high impedence (47k) signal and keeping the trigger high.

Change the cap that couples the Hall sensor to the 555 to 1 nF or 470pF range. Again, the high capacitance signal from the Hall sensor takes too long to drain the 10 nF cap and pulse the 555.

If the value of R4 can be changed, then I can suggest some different values. In any case, your current values do not generate a signal in my simulator.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Thank you.
The hall sensor circuit is unknown. It will not output a signal without pullup R3.


Changing R1 makes sense. I just copied the input circuit from "timer handbook".

Input demands of tachometer are also unknown. I just know that it responds to a wide range of signals from 3-30 volts. (from specs) If R4 is much over 100k it stops functioning. It may not be needed at all. It was added to reduce loading on 555 input circuit.

I've tried higher values of C2 and R3, but not lower value C2 and higher R1.

Thank you again. Might save me some components making a parallel circuit for tach output.

By the way, this circuit operates from 0-1khz only.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Changing values isn't helping.

I'll try to get some better data. Some of my assumptions may be off. Such as the swing of the hall output.

Using the 12v supply to the hall for my circuit by necessity. It's current limited thru a resistor in control. (assume)

Drops to 9v when connected to original hall circuit. My circuit doesn't affect it much.

It may be that my input pulse is swinging less than the 555 supply. (9v)
In that case I may adjust the control pin to raise the trigger threshold.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Biasing pin 2 to 1/2 vdd seems to work. 470k high and low from trigger.

With 9v supply, 6v pulse was needed to trigger. Now it triggers down to <5v with 9v supply.
Not as sensitive to other loads on hall output.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
As it's about the same project, I will try posting on the same thread.
Project does what I want with 555s and cmos logic.

On to the next phase.
I want to refresh my skills with the hope of using pics.

The way I started many years ago, with a much younger brain, was basic stamp first then "picbasic pro compiler".

Got out my old dos computer while waiting for basic stamp usb hardware.

Notice there are no recent stamp posts.
Yet, I have the activity boards etc. for stamp, so that's where I'll start.

I have some working divider programs in the bs2.
Need them to work up to 1khz input.
1 input.
1 divide by 4 output and one divide by 10-~500 output.

About 20 lines of basic code.
Using 2 "pulsout,1microsec" instructions.

It runs ok with 1 output.
With 2 it misses counts.

My question is:
Will it run ok in a faster pic?
BS2 is 4mhz

Or am I eating up to much time with the 2 pulsout instructions?

Lets see if anyone remembers BS2.
If not, maybe the Parallax forum?

tnx
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Have that part covered.
Now just a stamp/pic solution to divide by whole numbers.

Found my old compiler. Hope to dump stamp program into a pic today and see if it works.
 
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