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Need ideas for project

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I installed the attached circuit on the old Mazak turret lathe and it works 80% of the time. Here is the sequence:

1. The machine has a relay shown on page 1 bottom left labeled INDF which sends a +24 V signal to a voltage divider to produce a 12V clock pulse every time a tool change is called for. There are 8 tools on a turret.

2. Every time there is a clock pulse the 4022 outputs sequentially go high to + 5V from 0 to 7 for the tool being selected.

3. The corresponding outputs from the 2981 go high to + 24V and turn on the relay for that particular tool.

4. The output from the relay that is energized goes to the machine CNC control and is displayed on the operator monitor as the tool number that is currently active. That is the sole purpose of this circuit. To provide feedback to the operator as to what tool is currently

The circuit works fine 80% of the time, but occasionally when the clock signal goes from + 24V to 0V it acts like another clock pulse. So if you are using tool 2 and wish to go to tool 3 instead the relay for tool 4 turns on and the operator display shows tool 4 is active even though on the machine tool 3 is active. The ascending slope of the clock pulse is working good but sometimes the descending pulse is triggering the 4022 again.

To verify that this is what is occurring I installed a push button to simulate a clock pulse (shown lower right pg. 1). If I hold the push button in for 10 seconds or so the next relay led turns on as expected, but occasionally when I release the push button the next relay led lights up. So I know it is activated by the descending slope of the clock pulse.

What I am wondering about is the fact that the 4022 is using a + 5VDC power supply with VSS (pin 8) connected to the negative terminal of the power supply, not ground, whereas the 2981 is connected to GND for pin 10. Is this a problem? If not, any ideas on why there is an occasional extra clock pulse?
 

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  • M03 Circuit No. 4.pdf
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I put a .01uf capacitor from the junction of the two resistors to ground. Also, I replaced the 100k resistor connected to ground with a 67k resistor reducing the clock pulse from 12V to 6V. And finally, I connected the 5V power supply neg. terminal to ground.

The end result is that the machine ran an entire 8 hour shift without fail. I want to thank you all for your help. Couldn't have done it without you.
 
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