potentiometer output to on/off switch

You need a voltage comparator.

The circuit shown here will only drive a circuit of low current when on like around 10 ma's or so. if you need more, you can use a transistor to boost current. check back with the guys on that later on also, you can use an alternate part like a LM311 which can drive a small relay coil.

on this, you would need to connect the COM and VEE together when using a single ended supply. also, the output only sinks which means it pulls to common and does not source an output equal or near the power supply voltage.. This isn't a problem because you can thus pull AUX control line functions to common that have higher voltages than what this chip uses. For example, you can operate the chip at 5 volts and pull a load to common up to 40 volts.. This is more favorable when signaling various AUX equipment.

You may want recheck the values on the pots, those sizes sounds a bit on the low side.. Are you sure there isn't a "K" on the display on your meter? this would make more sense.. the readings you would be getting would then be 10K ohms and 6 K ohms. etc..

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Are the 3 pots totally separate, or are they interconnected in any way? Do you have all 3 terminals of each pot available, or does each only have 2?

These details will determine the kinds of circuits we can recommend.

Thanks for the responses. Voltage Comparitor sounds kind of like something Marty and the Doc would use on their time machine. :-) I

*think* I understand the concept...I'm comparing the pot to some voltage that I want, and when it hits the right voltage, the switch is open (in the example, lighting up the little light).

The readings are indeed 10k and 6k ohms, not 10 and 6 as I stated earlier. The meter was on the "x1k" setting.

There are 3 separate pots. Each has 3 leads. The motion of each pot when moving the joystick in the 3 directions does not fully extend the pots from full open to full close.

LOL. That should make it more fun to build one then !

This helps make the job that much easier.

That itself isn't a problem. You simply need to measure the active range and 'calibrate' the circuit accordingly.

Graham

Again, thx for the help. I've already learned more than I knew before.

I need to add that each pot actually represents an Axis, so there is a positive switch point and a negative switch point. Don't know if this makes a difference...I'm sure it does.

In the example you linked to, on the final diagram...the pot I want to compare (joystick axis) would go in place of the Windmill. Could I replace the pot in that last diagram with a 6k ohm resistor since this is the tipping point?

Well, that's actually a generator but I understand what you're talking about.

The generator produces voltages from 0 up to what ever. that circuit will switch on when the (+) input exceeds the (-) input.

What you need to do is if you plan on using the (-) for the pot input as it shows in the image. You need to place a fixed voltage that sets the window trip point on the (+) input.

Or, you could use the circuit as is and put the wiper of the pot in the joy stick on the (+) input, one outer connection on the common (ground), and the other outer connection of the pot on the +Voltage supply that is operating the comparator. In this case, you would need a

Trim pot on the (-) as you see it in the print to set the trip voltage.

So, if you were to place the joy stick in the middle, the wiper on one of the pots should be generating half of the supplied voltage, in this case 9 Volts.

You don't need to use a Trim pot as shown in the print for the (-) input, you can use a pair of resistors to form a voltage divider how ever, in your case where the POTS in the stick most likely are not perfectly aligned, you may want the trim pot on the (-) as shown to adjust your settings. A value of 10k is ok, you can use lower values also.

Now keep in mind with this simple circuit, the stick is only going to respond in one direct of the pot you connect it to.

If you're looking for lets say a window effect on one pot where you move left /right for example which should move the same pot, you would then need a "Window comparator". The simplest approach is to use the other OP-AMP that is in the 1458 part that is being used. You would build an equal circuit as the first one how ever, the inputs are reversed. For the pot from the stick, you would connect the wiper to the (-) input and the preset trim pot, you connect to the (+) input.. So what happens is this Op-amp will work in reverse logic as the other. If you want the 2 to drive a single common load, you need to use diodes on the output of each so that when one is off and the other is on, it won't short on each other..

This is where a LM393 series comes into play, since the output of this comparator is a open collector which means it sinks only (pulls to common), you can tie a number of these all together on their outputs to form a single signal. It also has 2 units in a 8 pin body so this makes it easy to use as a window comparator and in your case you would need 3 of these chips to do the window compare for all three pots unless you don't need a window compare and only a one sided compare.

This should give you something to think about :)

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