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Robust but simple, Latching Circuit needed!

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steevg

New Member
Robust but simple, Latching Circuit needed!

Hi,
This is my first visit to the forum (I'm only into hobby electronics - no formal training), and I'm hoping someone can help with what I think may be a fairly simple problem.

I have a joystick-type switch, it has four "momentary" positions with a centre "off" return. I need a circuit which will latch each position of the joystick, when I select it. So for example, if I select position 1, and release the "Joystick", I need the circuit to latch - this latch will hold an input to another part of the circuit to ground (0vDC).

If I then select position 2, I need the circuit to release from Position 1, and latch to Pos. 2. etc etc. I need to be able to select any position (1,2,3 or 4) at any time, and not have the latch drop out or disengage. On startup, it would be preferable to latch to position 1 by default.

The circuit needs to have little or no bounce, and be very robust with a fairly versatile range of operating temps - say -10 deg Celsius to + 50 deg Celsius.

Hope I've explained this clearly, and that someone may be able to provide me with a circuit to do the trick!

Thanks in advance!
 

MikeMl

Well-Known Member
Most Helpful Member
What happens if you move the joystick at an 45 deg angle and trip two switches simultaneously?

Ignoring the issue above, this should work:
 

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steevg

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Mike, thanks for your response, and a very good point!

The "Joystick" is a high quality aviation device, and I'm almost sure it's a break-before-make switch, but I'll check to see if this may be an issue.

Now that you've bought up this issue, I guess it would be wise to prepare for such an instance with another switch brand . . . it doesn't really matter if the switch moves to the next position or stays in it's current state, as long as it doesn't chatter between both.

Any idea how I could take this consideration in to account with this circuit?

Thanks again!
 

MikeMl

Well-Known Member
Most Helpful Member
...
The "Joystick" is a high quality aviation device, and I'm almost sure it's a break-before-make switch, but I'll check to see if this may be an issue.

Now that you've bought up this issue, I guess it would be wise to prepare for such an instance with another switch brand . . . it doesn't really matter if the switch moves to the next position or stays in it's current state, as long as it doesn't chatter between both.

Any idea how I could take this consideration in to account with this circuit.
How about putting a "priority encoder" behind the four flipflops? That way, if two channels become active, one channel would be given a higher priority than its neighbor.

If the switches in the joystick are form C, then the design would be more robust using a classical switch debounce circuit on each channel.
 

steevg

New Member
Mike, sounds fantastic, and perfect . . . . but you've lost me with the actual design!
I'm only a hobbyist . . . would you be able to modify your draing to show the actual wiring?

Thanks for your valuable time!
 

MikeMl

Well-Known Member
Most Helpful Member
Mike, sounds fantastic, and perfect . . . . but you've lost me with the actual design!
I'm only a hobbyist . . . would you be able to modify your draing to show the actual wiring?...
The drawing shows the actual wiring except for the extra voltage sources used to tickle the switches (the switches are in your joystick). The only detail I didn't do for you is to assign pin numbers to the specific ICs. You will have to look up the data sheets for those, and then allocate pins as needed. Dont forget the Vdd (5V power) and Vss (gnd) pins. You will need four chips, 2ea 74hc74 dual D Flip Flops, 1ea 74HC20 dual nand gate, 1ea 74HC14 schmitt-trigger hex inverter.
 
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steevg

New Member
Mike,

thanks so much for the very informative info.
I'll get to work this evening and check out the data sheets, and will post back to let you know how it goes.

Have a great week.

Warm regards,
Steve
 
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